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</head>
<body class="article">
<div id="header">
<h1>Virgo Programmer Guide</h1>
<div id="toc" class="toc">
<div id="toctitle">Table of Contents</div>
<ul class="sectlevel1">
<li><a href="#_preface">Preface</a></li>
<li><a href="#_prerequisites">Prerequisites</a>
<ul class="sectlevel2">
<li><a href="#_runtime_environment">Runtime Environment</a></li>
<li><a href="#_references">References</a></li>
</ul>
</li>
<li><a href="#_introduction_to_the_virgo_for_apache_tomcat">Introduction to the Virgo for Apache Tomcat</a>
<ul class="sectlevel2">
<li><a href="#_overview">Overview</a></li>
<li><a href="#_what_is_the_virgo_for_apache_tomcat">What is the Virgo for Apache Tomcat?</a></li>
<li><a href="#_why_the_virgo_for_apache_tomcat">Why the Virgo for Apache Tomcat?</a></li>
</ul>
</li>
<li><a href="#_deployment_architecture">Deployment Architecture</a>
<ul class="sectlevel2">
<li><a href="#_supported_deployment_formats">Supported Deployment Formats</a></li>
<li><a href="#_dependency_types">Dependency Types</a></li>
<li><a href="#_regions">Regions</a></li>
<li><a href="#_a_guide_to_forming_bundles">A Guide to Forming Bundles</a></li>
</ul>
</li>
<li><a href="#_developing_applications">Developing Applications</a>
<ul class="sectlevel2">
<li><a href="#_anatomy_of_a_bundle">Anatomy of a Bundle</a></li>
<li><a href="#_creating_pars_and_web_applications">Creating PARs and Web Applications</a></li>
<li><a href="#_creating_plans">Creating Plans</a></li>
<li><a href="#_creating_and_using_configuration_artifacts">Creating and Using Configuration Artifacts</a></li>
<li><a href="#_using_spring_and_gemini_blueprint">Using Spring and Gemini Blueprint</a></li>
<li><a href="#_programmatic_access_to_the_servlet_context">Programmatic Access to the Servlet Context</a></li>
<li><a href="#_web_application_manifest_processing">Web Application Manifest Processing</a></li>
<li><a href="#_working_with_dependencies">Working with Dependencies</a></li>
<li><a href="#_application_trace">Application Trace</a></li>
<li><a href="#_application_versioning">Application Versioning</a></li>
</ul>
</li>
<li><a href="#_migrating_to_osgi">Migrating to OSGi</a>
<ul class="sectlevel2">
<li><a href="#_migrating_web_applications">Migrating Web Applications</a></li>
<li><a href="#_migrating_to_a_plan_or_a_par">Migrating to a Plan or a PAR</a></li>
</ul>
</li>
<li><a href="#_case_study_migrating_the_form_tags_sample_application">Case Study: Migrating the Form Tags Sample Application</a>
<ul class="sectlevel2">
<li><a href="#_overview_of_the_form_tags_sample_application">Overview of the Form Tags Sample Application</a></li>
<li><a href="#_form_tags_war">Form Tags WAR</a></li>
<li><a href="#_form_tags_shared_libraries_war">Form Tags Shared Libraries WAR</a></li>
<li><a href="#_form_tags_shared_services_war">Form Tags Shared Services WAR</a></li>
<li><a href="#_form_tags_par">Form Tags PAR</a></li>
<li><a href="#_constructing_the_par">Constructing the PAR</a></li>
<li><a href="#_summary_of_the_form_tags_migration">Summary of the Form Tags Migration</a></li>
<li><a href="#_form_tags_as_a_plan">Form Tags as a Plan</a></li>
</ul>
</li>
<li><a href="#_working_with_common_enterprise_libraries">Working with Common Enterprise Libraries</a>
<ul class="sectlevel2">
<li><a href="#_working_with_hibernate">Working with Hibernate</a></li>
<li><a href="#_working_with_datasources">Working with DataSources</a></li>
<li><a href="#_weaving_and_instrumentation">Weaving and Instrumentation</a></li>
<li><a href="#_jsp_tag_libraries">JSP Tag Libraries</a></li>
</ul>
</li>
<li><a href="#_known_issues">Known Issues</a>
<ul class="sectlevel2">
<li><a href="#_jpa_entity_scanning">JPA Entity Scanning</a></li>
<li><a href="#__code_classnotfounderror_code_when_creating_a_proxy"><code>ClassNotFoundError</code> When Creating a Proxy</a></li>
<li><a href="#_creating_proxies_with_cglib_for_package_protected_types">Creating proxies with CGLIB for Package Protected Types</a></li>
<li><a href="#_virgo_jetty_server_restrictions">Virgo Jetty Server Restrictions</a></li>
<li><a href="#_default_web_application_bundle_headers">Default Web Application Bundle Headers</a></li>
<li><a href="#_hibernate_resolution_issue">Hibernate Resolution Issue</a></li>
<li><a href="#_scoping_and_substitutable_exports">Scoping and Substitutable Exports</a></li>
<li><a href="#_eclipselink_resolution_issue">EclipseLink Resolution Issue</a></li>
</ul>
</li>
</ul>
</div>
</div>
<div id="content">
<div id="preamble">
<div class="sectionbody">
<div class="paragraph">
<p>Ramnivas Laddad<br>
Colin Yates<br>
Sam Brannen<br>
Rob Harrop<br>
Christian Dupuis<br>
Andy Wilkinson<br>
Glyn Normington<br>
Steve Powell<br>
Christopher Frost<br>
Florian Waibel</p>
</div>
<div class="imageblock" style="float: right">
<div class="content">
<img src="assets/images/virgo-logo-small.png" alt="Eclipse Virgo">
</div>
</div>
<div class="paragraph">
<p>Eclipse Virgo<br>
3.7.1.RELEASE<br>
Copyright &#169; 2009, 2011 VMware Inc. and others</p>
</div>
<hr>
<!-- toc disabled -->
</div>
</div>
<div class="sect1">
<h2 id="_preface">Preface</h2>
<div class="sectionbody">
<div class="paragraph">
<p>Increasing complexity in modern enterprise applications is a fact of life.
Developers not only have to deal with complex business logic, but also a myriad
of other concerns such as security, auditing, exposing business
functionality to external applications, and managing the evolution of
these concerns. The Spring Framework addresses these
needs by offering a Plain-Old Java Object (POJO) based solution that
lets you focus on your business logic.</p>
</div>
<div class="paragraph">
<p>Complex applications pose problems that go beyond using the right set of
technologies. You need to take into account other considerations such as
a simplified development process, easy deployment, monitoring deployed
applications, and managing changes in response to changing business needs.
This is where the Eclipse Virgo comes into play. It offers a simple yet
comprehensive platform to develop, deploy, and service enterprise
applications. In this Programmer Guide, we explore the runtime portions of the
Eclipse Virgo, the Virgo for Apache Tomcat, Virgo Jetty Server and the
Virgo Kernel, and learn how to develop applications to benefit from their
capabilities.</p>
</div>
<div class="admonitionblock note">
<table>
<tr>
<td class="icon">
<div class="title">Note</div>
</td>
<td class="content">
<div class="title">For Virgo Kernel Programmers</div>
<div class="paragraph">
<p>Although this guide is written primarily for Virgo for Apache Tomcat programmers, much of it is also useful for
Virgo Kernel programmers who should simply ignore the web-related sections.</p>
</div>
</td>
</tr>
</table>
</div>
<div class="admonitionblock note">
<table>
<tr>
<td class="icon">
<div class="title">Note</div>
</td>
<td class="content">
<div class="title">For Virgo Nano Programmers</div>
<div class="paragraph">
<p>This guide is written primarily for Virgo for Apache Tomcat programmers. Although a base version of Virgo Nano, without the new provisioning
system, is used to build the Virgo for Apache Tomcat, much of this guide does not apply to Virgo Nano. The VN lacks regions support but has much
improved runtime footprint and startup time and also provides support for p2 provisioning. The Virgo Nano features are covered better in the
<a href="http://www.eclipse.org/virgo/documentation/virgo-documentation-$3.7.1.RELEASE/docs/virgo-user-guide/html/index.html">User Guide</a>.</p>
</div>
</td>
</tr>
</table>
</div>
<div class="paragraph">
<p><a id="prerequisites-references"></a></p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_prerequisites">Prerequisites</h2>
<div class="sectionbody">
<div class="sect2">
<h3 id="_runtime_environment">Runtime Environment</h3>
<div class="paragraph">
<p>Virgo requires Java SE 7 or later to be installed. Java is available from
<a href="http://www.oracle.com/technetwork/java/javase/downloads/index.html">Oracle</a> and elsewhere.</p>
</div>
</div>
<div class="sect2">
<h3 id="_references">References</h3>
<div class="paragraph">
<p>To make effective use of the Virgo for Apache Tomcat, you should also refer to the following:</p>
</div>
<div class="ulist">
<ul>
<li>
<p><a href="http://www.eclipse.org/virgo/documentation/virgo-documentation-3.7.1.RELEASE/docs/virgo-user-guide/html/index.html">User Guide</a></p>
</li>
<li>
<p><a href="http://www.eclipse.org/virgo/documentation/virgo-documentation-3.6.4.RELEASE/docs/virgo-tooling-guide/html/index.html">Tooling Guide</a></p>
</li>
<li>
<p><a href="https://www.osgi.org/developer/specifications/">Blueprint Container Specification</a>(in the OSGi 4.2 and 5.0 Enterprise Specifications)</p>
</li>
<li>
<p><a href="https://docs.spring.io/spring/docs/4.2.9.RELEASE/spring-framework-reference/">Spring Framework 4.2.9.RELEASE Reference Documentation</a></p>
</li>
</ul>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_introduction_to_the_virgo_for_apache_tomcat">Introduction to the Virgo for Apache Tomcat</h2>
<div class="sectionbody">
<div class="sect2">
<h3 id="_overview">Overview</h3>
<div class="paragraph">
<p>In this chapter, we provide an overview of the Virgo for Apache Tomcat focusing
on what it is, what benefits it provides to developers and administrators,
and why you should use it.</p>
</div>
<div class="paragraph">
<p><a id="introduction-what"></a></p>
</div>
</div>
<div class="sect2">
<h3 id="_what_is_the_virgo_for_apache_tomcat">What is the Virgo for Apache Tomcat?</h3>
<div class="paragraph">
<p>The Virgo for Apache Tomcat, or VTS for short, is the runtime portion of the Eclipse Virgo.
It is a lightweight, modular, OSGi-based runtime that provides a complete packaged solution for developing,
deploying, and managing enterprise applications.
By leveraging several best-of-breed technologies and improving upon
them, the VTS offers a compelling solution to develop and deploy
enterprise applications.</p>
</div>
<div class="paragraph">
<p><a id="introduction-constituents"></a></p>
</div>
<div class="sect3">
<h4 id="_what_makes_up_the_virgo_for_apache_tomcat">What Makes up the Virgo for Apache Tomcat?</h4>
<div class="paragraph">
<p>The Virgo for Apache Tomcat is built on top of the following core technologies:</p>
</div>
<div class="ulist">
<ul>
<li>
<p><a href="https://projects.spring.io/spring-framework/">Spring Framework</a>, obviously!</p>
</li>
<li>
<p><a href="http://tomcat.apache.org/">Tomcat</a> as the web container.</p>
</li>
<li>
<p><a href="http://www.osgi.org/Specifications/HomePage">OSGi R4.3</a>.</p>
</li>
<li>
<p><a href="http://www.eclipse.org/equinox/">Equinox</a> as the OSGi implementation.</p>
</li>
<li>
<p><a href="https://eclipse.org/gemini/blueprint/">Gemini Blueprint</a> for working with OSGi in a Spring application.</p>
</li>
<li>
<p><a href="http://www.eclipse.org/virgo/documentation/virgo-documentation-3.6.4.RELEASE/docs/virgo-tooling-guide/html/index.html">Tooling Guide</a> for developing applications.</p>
</li>
</ul>
</div>
<div class="paragraph">
<p>Note, however, that the Virgo for Apache Tomcat isn&#8217;t just a combination
of these technologies. Rather, it integrates and extends these
technologies to provide many features essential for developing,
deploying, and managing today&#8217;s enterprise Java applications.</p>
</div>
<div class="paragraph">
<p>The following diagram presents a high-level overview of the VTS&#8217;s architecture.</p>
</div>
<div class="paragraph">
<p><span class="image"><img src="assets/images/introduction-architecture.png" alt="introduction architecture"></span></p>
</div>
<div class="paragraph">
<p>At the heart of the Virgo for Apache Tomcat is the Virgo Kernel or VK.
The VK is an OSGi-based kernel that takes full advantage of the modularity
and versioning of the OSGi platform. The VK builds on a base version of Virgo Nano or VN and extends its capabilities for
provisioning and library management, as well as providing core functionality for the VTS. The VN maintains a minimal
runtime footprint and startup time. It builds on top of a pure Equinox, extending it with more sophisticated diagnostics and supportability functionality.
The VN supports full p2 provisioning. This feature is not included in the Virgo Nano Base that the VK is built on.</p>
</div>
<div class="paragraph">
<p>To maintain a minimal runtime footprint, OSGi bundles are installed on demand by the
VN. On subsequent restarts these core bundles are warm-started thus reducing the startup time. This allows for an application to be installed
into a running VTS and for its dependencies to be satisfied from an external repository. Not only
does this remove the need to manually install all your application dependencies, which would be tedious, but it also keeps memory usage to a minimum.</p>
</div>
<div class="paragraph">
<p>As shown in the figure, VK runs on top of VN that extends Equinox within a standard Java
Virtual Machine. Above the VK further layers contribute functionality
to the VTS. Such as management and web application support.</p>
</div>
<div class="paragraph">
<p>Version 3.7.1.RELEASE of the Virgo for Apache Tomcat supports <strong>bundle</strong>,
<strong>plan</strong>, <strong>PAR</strong>, <strong>configuration</strong>,
<strong>Web Application Bundle (WAB)</strong>, and <strong>WAR</strong> artifacts, which enable
you to build sophisticated web applications. This includes support for
standard Java EE WARs, "shared library" WARs, and "shared services" WARs, each of
which will be covered in greater detail in <a href="#architecture">Deployment Architecture</a>.</p>
</div>
<div class="admonitionblock important">
<table>
<tr>
<td class="icon">
<div class="title">Important</div>
</td>
<td class="content">
<div class="paragraph">
<p>The Virgo Nano has a different provisioning system which isn&#8217;t included in the Virgo Nano Base on which the
VK and the VTS are built.</p>
</div>
</td>
</tr>
</table>
</div>
<div class="paragraph">
<p>Version 3.7.1.RELEASE of the Virgo Nano supports <strong>bundle</strong>,
<strong>p2 feature</strong>, <strong>Web Application Bundle (WAB)</strong>, and <strong>WAR</strong> artifacts, which enable
you to build sophisticated web applications too, taking full advantage of p2&#8217;s dependency resolution, automated download and fail-early mechanics.
The Virgo Nano does NOT support <strong>plan</strong>, <strong>PAR</strong> or <strong>configuration</strong> artifacts.
New <strong>features</strong> are provisioned via <strong>update sites</strong> or <strong>p2 repositories</strong>.
Brief overview of p2 and it&#8217;s mechanics is available on <a href="http://bkapukaranov.wordpress.com/2011/07/12/rt-meets-p2/">this blog</a>.
The VN&#8217;s default web container implementation is Gemini Web.</p>
</div>
<div class="paragraph">
<p><a id="introduction-why"></a></p>
</div>
</div>
</div>
<div class="sect2">
<h3 id="_why_the_virgo_for_apache_tomcat">Why the Virgo for Apache Tomcat?</h3>
<div class="paragraph">
<p>You could deploy a web application in a stand-alone servlet engine or application server.
Or you could even deploy directly in an OSGi container such as Equinox. However,
deploying in the Virgo for Apache Tomcat offers a number of key benefits that make it both more
appealing and more suitable for enterprise application development.</p>
</div>
<div class="paragraph">
<p><a id="introduction-unified-deployment"></a></p>
</div>
<div class="sect3">
<h4 id="_deployment_options_and_migration_paths">Deployment Options and Migration Paths</h4>
<div class="paragraph">
<p>While many applications deployed in the Virgo for Apache Tomcat will take advantage
of OSGi capabilities, not all applications need such sophistication.
For example, development teams may initially choose to continue packaging
existing web applications as standard WAR files and then gradually migrate
toward a fully OSGi-based packaging and deployment model. The Virgo for Apache Tomcat
makes such migrations easy for developers by supporting multiple packaging
and deployment formats. These formats and migration strategies are discussed
in greater detail in <a href="#migrating-to-osgi">Migrating to OSGi</a> and
<a href="#formtags-case-study">Case Study: Migrating the Form Tags Sample Application</a>.</p>
</div>
<div class="paragraph">
<p><a id="introduction-simplified-deployment"></a></p>
</div>
</div>
<div class="sect3">
<h4 id="_simplified_development_and_deployment_of_osgi_based_applications">Simplified Development and Deployment of OSGi-based Applications</h4>
<div class="paragraph">
<p>Prior to the release of the Virgo for Apache Tomcat, developing and deploying OSGi
applications involved inherent complexity such as:</p>
</div>
<div class="ulist">
<ul>
<li>
<p><strong>Obtaining OSGi bundles for popular Java libraries:</strong>
For optimal benefits, every technology you use in an OSGi application must
be packaged as OSGi bundles. Sometimes, this involves manually converting
JAR files into bundles and making sure that any libraries needed by those
bundles are also available as OSGi bundles. The <a href="http://www.eclipse.org/ebr">EBR</a> is a good source of
popular pre-bundled libraries.</p>
</li>
<li>
<p><strong>Package management complexity:</strong>
OSGi bundles use other bundles through <code>Import-Package</code> manifest headers.
Many applications use a set of common technologies (e.g., an ORM solution,
a web framework, etc.). Combining these two characteristics leads to duplicated
configuration in the form of repeated and verbose <code>Import-Package</code> statements.</p>
</li>
<li>
<p><strong>Lack of application-level isolation:</strong>
In OSGi everything is a bundle, and all bundles share the same OSGi Service Registry.
To highlight how conflicts can arise between applications and their services in this
shared service registry, consider the following scenarios.</p>
<div class="ulist">
<ul>
<li>
<p>Application <code>A</code> is comprised of bundles <code>B</code> and <code>C</code>.
In a standard OSGi environment, if you attempt to install two instances of the same
version of application <code>A</code> (i.e., two sets of bundles <code>B</code> and
<code>C</code>), a clash will occur, because you cannot deploy multiple bundles with
the same <code>Bundle-SymbolicName</code> and <code>Bundle-Version</code> combination.</p>
</li>
<li>
<p>Application <code>A1</code> is comprised of bundles <code>B1</code> and <code>C1</code>.
Similarly, application <code>A2</code> is comprised of bundles <code>B2</code> and <code>C2</code>.
Each bundle has a unique combination of <code>Bundle-SymbolicName</code> and <code>Bundle-Version</code>.
Bundles <code>B1</code> and <code>B2</code> both export service <code>S</code> which
is imported by both <code>C1</code> and <code>C2</code>. In contrast to the previous
example, there is no conflict resulting from duplicate
<code>Bundle-SymbolicName</code>/<code>Bundle-Version</code> combinations; however,
there is a clash for the exported service <code>S</code>.
Which service <code>S</code> will bundles <code>C1</code> and <code>C2</code> end up
using once they are installed?
Assuming bundles <code>B1</code> and <code>C1</code> are intended to work together,
you would not want bundle <code>C1</code> to get a reference to service <code>S</code>
from bundle <code>B2</code>, because it is installed in a different logical application.
On the contrary, you typically want bundle <code>C1</code> to get a reference to
service <code>S</code> exported by bundle <code>B1</code>, but in a standard OSGi environment
this may not be the case.</p>
</li>
</ul>
</div>
</li>
</ul>
</div>
<div class="paragraph">
<p>Furthermore, since standard OSGi does not define a notion of an application as a set of bundles,
you cannot deploy or undeploy an application and its constituent bundles as a single unit.</p>
</div>
<div class="paragraph">
<p>The Virgo for Apache Tomcat introduces a number of features to solve these issues:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>A full set of OSGi bundles for many popular Java libraries to get you
started quickly with creating OSGi applications.</p>
</li>
<li>
<p>An OSGi library concept that obviates the need to
duplicate verbose <code>Import-Package</code> statements.</p>
</li>
<li>
<p>The PAR packaging format which offers
application-level isolation and deployment.</p>
</li>
<li>
<p>The concept of a plan, which is an XML file that lists a collection of bundles that Virgo for Apache Tomcat should load together as a single application. Conceptually, plans are very like PARs, except that a plan describes the contents of the application rather than a PAR that actually contains them.</p>
</li>
</ul>
</div>
<div class="paragraph">
<p><a id="introduction-diagnostics"></a></p>
</div>
</div>
<div class="sect3">
<h4 id="_enhanced_diagnostics_during_deployment_and_in_production">Enhanced Diagnostics During Deployment and in Production</h4>
<div class="paragraph">
<p>Identifying why an application won&#8217;t deploy or which particular library
dependencies are unsatisfied is the cause of many headaches!
Similarly, production time errors that don&#8217;t identify the root cause are
all too familiar to Java developers. The VTS was designed from the
ground up to enable tracing and First Failure Data Capture (FFDC) that
empower developers with precise information at the point of failure to
fix the problem quickly.</p>
</div>
<div class="paragraph">
<p><a id="architecture"></a></p>
</div>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_deployment_architecture">Deployment Architecture</h2>
<div class="sectionbody">
<div class="paragraph">
<p>The Virgo for Apache Tomcat offers several choices when it comes to deploying applications. Each
choice offers certain advantages, and it is important to understand those in order to make
the right choice for your application. In this chapter, we take a closer look at the choices
offered, compare them, and provide guidelines in choosing the right one based on your
specific needs.</p>
</div>
<div class="paragraph">
<p>The VTS supports standard self-contained WAR files thus allowing you to
use the Virgo for Apache Tomcat as an enhanced web server. The VTS also supports the
<strong>Shared Libraries</strong> WAR format which allows for slimmer WAR files that
depend on OSGi bundles instead of including JAR files inside the WAR. The <strong>Shared
Services</strong> WAR format allows developers to further reduce the complexity of
standard WARs by deploying services and infrastructure bundles alongside the WAR. A shared
services WAR will then consume the services published by those bundles. To complete the
picture, the VTS supports the new OSGi-standard <strong>Web Application
Bundle</strong> deployment format for web applications that builds on the benefits
provided by a shared services WAR. In addition to this, VTS provides
additional conveniences for developing and deploying Spring MVC-based web applications.</p>
</div>
<div class="paragraph">
<p>For applications consisting of multiple bundles and web applications, plans and the PAR
format are the primary deployment models that take advantage of OSGi capabilities. We will
explore all of these formats and their suitability later in this guide.</p>
</div>
<div class="paragraph">
<p><a id="architecture-deployment-formats"></a></p>
</div>
<div class="sect2">
<h3 id="_supported_deployment_formats">Supported Deployment Formats</h3>
<div class="paragraph">
<p>The Virgo for Apache Tomcat supports applications packaged in the following formats:</p>
</div>
<div class="olist arabic">
<ol class="arabic">
<li>
<p><a href="#architecture-raw-osgi-bundles">Raw OSGi Bundles</a></p>
</li>
<li>
<p><a href="#architecture-wars">Java EE WAR</a></p>
</li>
<li>
<p><a href="#architecture-war-gemini">Web Application Bundles</a></p>
</li>
<li>
<p><a href="#architecture-pars">PARs</a></p>
</li>
<li>
<p><a href="#architecture-plans">Plans</a></p>
</li>
<li>
<p><a href="#architecture-configurations">Configurations</a></p>
</li>
</ol>
</div>
<div class="paragraph">
<p>When you deploy an application to the VTS, each deployment artifact
(e.g., a single bundle, WAR, PAR, or plan) passes through a deployment pipeline. This
deployment pipeline is responsible for processing applications of certain types (i.e.,
application type). The 3.7.1.RELEASE release of the VTS natively
supports deployers analogous to each of the aforementioned packaging options.</p>
</div>
<div class="paragraph">
<p>Let&#8217;s take a closer look now at each of the supported deployment and packaging
options to explore which one is best suited to your application.</p>
</div>
<div class="paragraph">
<p><a id="architecture-raw-osgi-bundles"></a></p>
</div>
<div class="sect3">
<h4 id="_raw_osgi_bundles">Raw OSGi Bundles</h4>
<div class="paragraph">
<p>At its core, the Virgo for Apache Tomcat is an OSGi container. Thus any OSGi-compliant
bundle can be deployed directly on the VTS unmodified. You&#8217;ll
typically deploy an application as a single bundle or a set of stand-alone bundles
if you&#8217;d like to publish or consume services globally within the container via
the OSGi Service Registry.</p>
</div>
<div class="paragraph">
<p><a id="architecture-wars"></a></p>
</div>
</div>
<div class="sect3">
<h4 id="_war_deployment_formats">WAR Deployment Formats</h4>
<div class="paragraph">
<p>For Web Application Archives (WAR), the Virgo for Apache Tomcat provides support for the
following three formats.</p>
</div>
<div class="olist arabic">
<ol class="arabic">
<li>
<p><a href="#architecture-standard-war">Standard WAR</a></p>
</li>
<li>
<p><a href="#architecture-shared-libraries-war">Shared Libraries WAR</a></p>
</li>
<li>
<p><a href="#architecture-shared-services-war">Shared Services WAR</a></p>
</li>
</ol>
</div>
<div class="paragraph">
<p>Each of these formats plays a distinct role in the incremental migration path
from a standard Java EE WAR to an OSGi-ified web application.</p>
</div>
<div class="paragraph">
<p><a id="architecture-standard-war"></a></p>
</div>
</div>
<div class="sect3">
<h4 id="_standard_war">Standard WAR</h4>
<div class="paragraph">
<p>Standard WAR files are supported directly in the VTS. At
deployment time, the WAR file is transformed into an OSGi bundle and installed
into Tomcat. All the standard WAR contracts are honoured, and your existing WAR
files should just drop in and deploy without change. Support for standard,
unmodified WAR files allows you to try out the Virgo for Apache Tomcat on your existing
web applications and then gradually migrate toward the <strong>Shared
Libraries WAR</strong> and <strong>Shared Services WAR</strong> formats.</p>
</div>
<div class="paragraph">
<p>In addition to the standard support for WARs that you would expect from
Tomcat, the VTS also enables the following features:</p>
</div>
<div class="olist arabic">
<ol class="arabic">
<li>
<p>Spring-driven load-time weaving (see Section 6.8.4, “Load-time weaving
with AspectJ in the Spring Framework").
Diagnostic information such as FFDC (first failure data capture)</p>
</li>
<li>
<p>The main benefit of this application style is familiarity&#8201;&#8212;&#8201;developers know
how to create a WAR file! You can take advantage of the
VTS&#8217;s added feature set without modifying the
application. The application can also be deployed on other Servlet containers or
Java EE application servers.</p>
</li>
</ol>
</div>
<div class="paragraph">
<p>You may choose this application style if the application is fairly simple and
small. You may also prefer this style even for large and complex applications as
a starting point and migrate to the other styles over time as discussed in <a href="#migrating-to-osgi">Migrating to OSGi</a>.</p>
</div>
<div class="paragraph">
<p><a id="architecture-shared-libraries-war"></a></p>
</div>
</div>
<div class="sect3">
<h4 id="_shared_libraries_war">Shared Libraries WAR</h4>
<div class="paragraph">
<p>If you have experience with developing and packaging web applications using
the standard WAR format, you&#8217;re certainly familiar with the pains of
library bloat. So, unless you&#8217;re installing shared libraries in a common
library folder for your Servlet container, you have to pack all JARs required by
your web application in <code>/WEB-INF/lib</code>. Prior to the release of
the Virgo for Apache Tomcat, such library bloat has essentially been the norm for web
applications, but now there is a better solution! The Shared Libraries WAR
format reduces your application&#8217;s deployment footprint and eradicates
library bloat by allowing you to declare dependencies on libraries via standard
OSGi manifest headers such as <code>Import-Package</code> and <code>Require-Bundle</code> . The VTS provides additional
support for simplifying dependency management via the <code>Import-Library</code> and <code>Import-Bundle</code> manifest headers
which are essentially macros that get expanded into OSGi-compliant <code>Import-Package</code> statements.</p>
</div>
<div class="admonitionblock tip">
<table>
<tr>
<td class="icon">
<div class="title">Tip</div>
</td>
<td class="content">
<div class="paragraph">
<p>For detailed information on which libraries are already available, check
out the <a href="http://www.eclipse.org/ebr">EBR</a>.</p>
</div>
</td>
</tr>
</table>
</div>
<div class="paragraph">
<p><a id="architecture-shared-services-war"></a></p>
</div>
</div>
<div class="sect3">
<h4 id="_shared_services_war">Shared Services WAR</h4>
<div class="paragraph">
<p>Once you&#8217;ve begun taking advantage of declarative dependency management
with a Shared Libraries WAR, you&#8217;ll likely find yourself wanting to take
the next step toward reaping further benefits of an OSGi container: sharing
services between your OSGi-compliant bundles and your web applications. By
building on the power and simplicity of Gemini Blueprint, the <strong>Shared Services
WAR</strong> format puts the OSGi Service Registry at your finger tips. As
a best practice you&#8217;ll typically publish services from your domain,
service, and infrastructure bundles via <code>&lt;osgi:service &#8230;&#8203;&gt;</code> and then consume them in your web application&#8217;s
ApplicationContext via <code>&lt;osgi:reference &#8230;&#8203; &gt;</code>. Doing so
promotes programming to interfaces and allows you to completely decouple your
web-specific deployment artifacts from your domain model, service layer, etc.,
and that&#8217;s certainly a step in the right direction. Of the three supported
WAR deployment formats, the Shared Services WAR is by far the most attractive in
terms of modularity and reduced overall footprint of your web applications.</p>
</div>
<div class="paragraph">
<p><a id="architecture-war-gemini"></a></p>
</div>
</div>
<div class="sect3">
<h4 id="_wars_and_the_gemini_web_container">WARs and the Gemini Web Container</h4>
<div class="paragraph">
<p>Virgo for Apache Tomcat fully supports the OSGi Web Applications standard. Using the
reference implementation from Gemini Web that was developed by SpringSource from
an offshoot of the original VTS codebase. This RI is now fully
integrated in VTS as the basis of the support for web
application deployment.</p>
</div>
<div class="paragraph">
<p>The OSGi Web Applications specification introduces the concept of a <strong>Web
Application Bundle</strong>, which is a WAR that is also a bundle. The
specification defines how WAR files are transformed into bundles automatically
as needed.</p>
</div>
<div class="paragraph">
<p>You can find an introduction to the Web Container in blog entries written by
the Virgo team <a href="http://blog.springsource.com/2009/05/27/introduction-to-the-osgi-web-container/">here</a>
and <a href="http://blog.springsource.com/2009/06/01/what-the-osgi-web-container-means-for-dm-server/">here</a>.</p>
</div>
<div class="paragraph">
<p><a id="architecture-war-gemini-extensions"></a></p>
</div>
</div>
<div class="sect3">
<h4 id="_extensions_to_the_web_container">Extensions to the Web Container</h4>
<div class="paragraph">
<p>Virgo for Apache Tomcat provides a variety of extensions to the Web Container that
allow you to construct sophisticated applications. The table below
summarises the extensions that are available or in development.</p>
</div>
<table class="tableblock frame-all grid-all spread">
<colgroup>
<col style="width: 50%;">
<col style="width: 50%;">
</colgroup>
<thead>
<tr>
<th class="tableblock halign-left valign-top">Feature</th>
<th class="tableblock halign-left valign-top">Description</th>
</tr>
</thead>
<tbody>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">Instrumentable ClassLoaders</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">All web bundle ClassLoaders are
instrumentable by Spring&#8217;s load-time weaving infrastructure.</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">Support for exploded bundles/WARs</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Bundles/WARs in directory form can
be deployed as Web Application Bundles</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">Support for scanning TLDs in dependencies</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">As per the Web Application
specification, all TLDs located inside a web bundle are located using
the rules defined in the JSP 2.1 specification. In
VTS, the dependencies of a Web Application
Bundle are also scanned for TLDs following the rules outlined in JSP 2.1</p></td>
</tr>
</tbody>
</table>
<div class="paragraph">
<p><a id="architecture-pars"></a></p>
</div>
</div>
<div class="sect3">
<h4 id="_par">PAR</h4>
<div class="paragraph">
<p>A PAR is a standard JAR which contains all of the modules of your application
(e.g., service, domain, and infrastructure bundles as well as a WAR or web module
for web applications) in a single deployment unit. This allows you to deploy,
refresh, and undeploy your entire application as a single entity. If you are
familiar with Java EE, it is worth noting that a PAR can be considered a replacement
for an EAR (Enterprise Archive) within the context of an OSGi container. As an added
bonus, modules within a PAR can be refreshed independently and on-the-fly, for
example via the Virgo Eclipse IDE Tooling (see the Virgo Tools Guide).</p>
</div>
<div class="paragraph">
<p>Many of the benefits of the PAR format are due to the underlying OSGi
infrastructure, including:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>Fundamentally modularized applications: instead of relying on fuzzy
boundaries between logical modules in a monolithic application, this
style promotes physically separated modules in the form of OSGi bundles.
Then each module may be developed separately, promoting parallel
development and loose coupling.</p>
</li>
<li>
<p>Robust versioning of various modules: the versioning capability
offered by OSGi is much more comprehensive than alternatives. Each
module can specify a version range for each of its dependencies. Bundles
are isolated from each other in such a way that multiple versions of a
bundle may be used simultaneously in an application.</p>
</li>
<li>
<p>Improved manageability: each bundle may be deployed or undeployed in
a running application. This allows modifying the existing application to
fix bugs, improve performance, and even to add new features without
having to restart the application.</p>
</li>
</ul>
</div>
<div class="paragraph">
<p>Furthermore, PARs scope the bundles of your application within the
VTS. Scoping provides both a physical and logical application
boundary, effectively shielding the internals of your application from other PARs
deployed within the VTS. This means your application doesn&#8217;t
have to worry about clashing with other running applications (e.g., in the OSGi
Service Registry). You get support for load-time weaving, classpath scanning,
context class loading, etc., and the VTS does the heavy lifting for
you to make all this work seamlessly in an OSGi environment. If you want to take
full advantage of all that the Virgo for Apache Tomcat and OSGi have to offer, packaging and
deploying your applications as a PAR is a good choice, although plans are an even
better one, as described in the next section.</p>
</div>
<div class="admonitionblock tip">
<table>
<tr>
<td class="icon">
<div class="title">Tip</div>
</td>
<td class="content">
<div class="title">OSGi != multiple JARs</div>
<div class="paragraph">
<p>Note that while physically separated modules can, in theory, be implemented
simply using multiple JARs, complex versioning requirements often make this
impractical. For example, consider the situation depicted in the diagram below.</p>
</div>
<div class="ulist">
<ul>
<li>
<p>Bundle A depends on version <code>1.0.0</code> of bundle <code>B</code> and version <code>2.0.0</code> of bundle <code>C</code>.</p>
</li>
<li>
<p>Bundle B depends on version <code>1.0.0</code> of bundle <code>C</code>.</p>
</li>
</ul>
</div>
<div class="paragraph">
<p>Suppose that versions <code>1.0.0</code> and <code>2.0.0</code> of bundle <code>C</code> are neither
backward nor forward compatible. Traditional monolithic applications cannot
handle such situations: either bundle <code>A</code> or bundle <code>B</code> would need reworking which
undermines truly independent development. OSGi&#8217;s versioning scheme enables
this scenario to be implemented in a robust manner. If it is desirable to rework
the application to share a single version of <code>C</code>, then this can be planned in and
is not forced.</p>
</div>
<div class="imageblock">
<div class="content">
<img src="assets/images/architecture-bundle-versioning.png" alt="architecture bundle versioning">
</div>
</div>
</td>
</tr>
</table>
</div>
<div class="paragraph">
<p><a id="architecture-plans"></a></p>
</div>
</div>
<div class="sect3">
<h4 id="_plans">Plans</h4>
<div class="paragraph">
<p>A plan is similar to a PAR in that it encapsulates all of the artifacts of your
application in a single deployment unit. The main difference, however, is that a
plan is simply an XML file that lists the artifacts of your application; a PAR, by
contrast, is an actual JAR file that physically contains the artifacts. Just like a
PAR, you deploy, refresh, and undeploy a plan as a single entity. We highly
recommends the use of plans for creating applications.</p>
</div>
<div class="paragraph">
<p>When you create a plan, you can specify that the included bundles and services
are in a scope that isolates them from the rest of Virgo for Apache Tomcat and its
deployments. This scoping ensures that the bundles wire to each other and see each
other&#8217;s services in preference to services from outside the scope. Scoping
also prevents application code from leaking into the global scope or scope of
another application. In addition, a plan can link the lifecycle of a group of
bundles together atomically, which ensures that start, stop, and uninstall
events on a single artifact in the plan are escalated to all artifacts in the plan.
You can, however, disable both of these features by simply setting an attribute in
the plan.</p>
</div>
<div class="paragraph">
<p>The general benefits of using plans are similar to those of using PARs; see <a href="#architecture-pars">PAR</a> for details. Plans offer added benefits,
however, such as the ability to control the deployment order of your application:
the order in which you list artifacts in the plan&#8217;s XML file is the order in
which VTS deploys them. Additionally, because plans specify the
artifacts that make up an application by reference, it is easier to share artifacts
between plans as well as update individual parts of a plan without having to
physically repackage (re-JAR) it.</p>
</div>
<div class="paragraph">
<p><a id="architecture-configurations"></a></p>
</div>
</div>
<div class="sect3">
<h4 id="_configurations">Configurations</h4>
<div class="paragraph">
<p>A Configuration is simply a Java properties file. When deployed it will be
recognised by the deployer and installed in to <strong>Configuration
Admin</strong> for later use by your applications. VTS supports
both singleton (ManagedService) and factory (ManagedServiceFactory) configurations.
(see section 104.6 in the Compendium Specification)</p>
</div>
<div class="paragraph">
<p>For a singleton configuration the name that it will be installed under is its filename
minus the <code>.properties</code> extension. Factory Configuration is supported by
specifying the <strong>service.factoryPid</strong> property. In this case the actual PID will
be created by <strong>Configuration Admin</strong> (see section 104.6 in the
Compendium Specification).</p>
</div>
<div class="paragraph">
<p>How to consume configuration data is discussed <a href="#developing-applications-configuration-artifacts">later</a>.</p>
</div>
<div class="paragraph">
<p><a id="architecture-dependency-types"></a></p>
</div>
</div>
</div>
<div class="sect2">
<h3 id="_dependency_types">Dependency Types</h3>
<div class="paragraph">
<p>In an OSGi environment, there are two kinds of dependencies between various bundles:
<strong>type</strong> dependency and <strong>service</strong> dependency.</p>
</div>
<div class="ulist">
<ul>
<li>
<p><strong>Type dependency</strong>: A bundle may depend on a
type exported by another bundle thus creating a type dependency. Type
dependencies are managed through <code>Import-Package</code> and
<code>Export-Package</code> directives in the OSGi manifest. This
kind of dependency is similar to a JAR file using types in other JAR files
from the classpath. However, as we&#8217;ve seen earlier, there are
significant differences.</p>
</li>
<li>
<p><strong>Service dependency</strong>: A bundle may also
publish services (preferably using Gemini Blueprint), and other bundles may consume
those services. If two bundles depend on the same service, both will be
communicating effectively to the same object. More specifically, any state
for that service will be shared between all the clients of that service.
This kind of arrangement is similar to the commonly seen client-server
interaction through mechanisms such as RMI or Web Services.</p>
</li>
</ul>
</div>
</div>
<div class="sect2">
<h3 id="_regions">Regions</h3>
<div class="paragraph">
<p>Conceptually, the Eclipse Virgo can be divided into two separate subsystems, called Regions. This
provides a way to keep the Virgo Kernel separate from user applications. Read more about Regions
and the two in Virgo in the <a href="http://www.eclipse.org/virgo/documentation/virgo-documentation-3.7.1.RELEASE/docs/virgo-user-guide/html/index.html">User Guide</a>
concepts section.</p>
</div>
<div class="paragraph">
<p><a id="architecture-forming-bundles"></a></p>
</div>
</div>
<div class="sect2">
<h3 id="_a_guide_to_forming_bundles">A Guide to Forming Bundles</h3>
<div class="paragraph">
<p>So what makes an application suitable for deployment on the Virgo for Apache Tomcat? Since
OSGi is at the heart of the VTS, modular applications consisting of
bundles, which each represent distinct functionality and well-defined boundaries, can
take maximum advantage of the OSGi container&#8217;s capabilities. The core ideas behind
forming bundles require following good software engineering practices: separation of
concerns, loose coupling, and communication through clear interfaces. In this section,
we look at a few approaches that you may use to create modular applications for
Virgo for Apache Tomcat deployment. Please consider the following discussion as guidelines and
not as rules.</p>
</div>
<div class="paragraph">
<p>Bundles can be formed along horizontal slices of layering and vertical slices of
function. The objective is to enable independent development of each bundle and minimize
the skills required to develop each bundle.</p>
</div>
<div class="paragraph">
<p>For example, an application could have the following bundles:
<strong>infrastructure</strong>, <strong>domain</strong>,
<strong>repository</strong>, <strong>service</strong>, and
<strong>web</strong> as shown in the following diagram.</p>
</div>
<div class="imageblock">
<div class="content">
<img src="assets/images/bundle-dependencies-layers.png" alt="bundle dependencies layers">
</div>
</div>
<div class="paragraph">
<p>Each bundle consists of types appropriate for that layer and exports
packages and services to be used by other layers. Let&#8217;s examine each bundle in
more detail:</p>
</div>
<table class="tableblock frame-all grid-all spread">
<caption class="title">Table 1. Bundles across layers</caption>
<colgroup>
<col style="width: 20%;">
<col style="width: 20%;">
<col style="width: 20%;">
<col style="width: 20%;">
<col style="width: 20%;">
</colgroup>
<thead>
<tr>
<th class="tableblock halign-left valign-top">Bundles</th>
<th class="tableblock halign-left valign-top">Imported Packages</th>
<th class="tableblock halign-left valign-top">Exported Packages</th>
<th class="tableblock halign-center valign-top">Consumed Services</th>
<th class="tableblock halign-center valign-top">Published Services</th>
</tr>
</thead>
<tbody>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">Infrastructure</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Third-party libraries</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Infrastructure interfaces</p></td>
<td class="tableblock halign-center valign-top"><p class="tableblock">None</p></td>
<td class="tableblock halign-center valign-top"><p class="tableblock">None</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">Domain</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Depends: for example,
if JPA is used to
annotate persistent
types, then JPA
packages.</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Public domain types</p></td>
<td class="tableblock halign-center valign-top"><p class="tableblock">None</p></td>
<td class="tableblock halign-center valign-top"><p class="tableblock">None</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">Web</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Domain, Service</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">None</p></td>
<td class="tableblock halign-center valign-top"><p class="tableblock">Service beans</p></td>
<td class="tableblock halign-center valign-top"><p class="tableblock">None</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">Service</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Domain,
Infrastructure,
Repository</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Service interfaces</p></td>
<td class="tableblock halign-center valign-top"><p class="tableblock">Repository beans</p></td>
<td class="tableblock halign-center valign-top"><p class="tableblock">Service beans</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">Repository</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Domain,
Third-party libraries,
ORM bundles, etc.</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Repository interfaces</p></td>
<td class="tableblock halign-center valign-top"><p class="tableblock">DataSources,
ORM session/entity managers,
etc.</p></td>
<td class="tableblock halign-center valign-top"><p class="tableblock">Repository beans</p></td>
</tr>
</tbody>
</table>
<div class="paragraph">
<p>Within each layer, you may create bundles for each subsystem representing a vertical
slice of business functionality. For example, as shown in the following figure, the
service layer is divided into two bundles each representing separate business
functions.
<span class="image"><img src="assets/images/bundle-dependencies-verticals.png" alt="bundle dependencies verticals"></span></p>
</div>
<div class="paragraph">
<p>You can similarly separate the repositories, domain classes, and web controllers
based on the business role they play.</p>
</div>
<div class="paragraph">
<p><a id="developing-applications"></a></p>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_developing_applications">Developing Applications</h2>
<div class="sectionbody">
<div class="paragraph">
<p>Applications that take advantage of the OSGi capabilities of Virgo
are typically comprised of multiple bundles. Each bundle may have dependencies on
other bundles. Furthermore, each bundle exposes only certain packages and
services. In this chapter, we look at how to create bundles, import and export
appropriate functionality, and create artifacts to deploy web applications on the Virgo for Apache Tomcat.</p>
</div>
<div class="paragraph">
<p><a id="developing-applications-bundle"></a></p>
</div>
<div class="sect2">
<h3 id="_anatomy_of_a_bundle">Anatomy of a Bundle</h3>
<div class="admonitionblock tip">
<table>
<tr>
<td class="icon">
<div class="title">Tip</div>
</td>
<td class="content">
<div class="paragraph">
<p>This is an abbreviated introduction to OSGi bundles. Please refer to the <a href="https://www.eclipse.org/gemini/blueprint/documentation/reference/2.0.0.RELEASE/html/index.html">Eclipse Gemini Blueprint Reference Guide</a> for full details.</p>
</div>
</td>
</tr>
</table>
</div>
<div class="paragraph">
<p>An OSGi bundle is simply a jar file with metadata that describe
additional characteristics such as version and imported and exported packages.</p>
</div>
<div class="paragraph">
<p>A bundle exports types and publishes services to be used by other bundles:</p>
</div>
<div class="ulist">
<ul>
<li>
<p><strong>Types</strong>: via the OSGi <code>Export-Package</code> directive,</p>
</li>
<li>
<p><strong>Services</strong>: via Gemini Blueprint&#8217;s <code>&lt;service &#8230;&#8203; &gt;</code> XML namespace element.</p>
</li>
</ul>
</div>
<div class="paragraph">
<p>A bundle may import types and services exported by other bundles:</p>
</div>
<div class="ulist">
<ul>
<li>
<p><strong>Types</strong>: via the OSGi <code>Import-Package</code> directive,</p>
</li>
<li>
<p><strong>Services</strong>: via Gemini Blueprint&#8217;s <code>&lt;reference &#8230;&#8203; &gt;</code> XML namespace element.</p>
</li>
</ul>
</div>
<div class="paragraph">
<p>Let&#8217;s see an example from the PetClinic sample application. The following listing shows the
<code>MANIFEST.MF</code> file for the <code>org.springframework.petclinic.infrastructure.hsqldb</code> bundle.</p>
</div>
<div class="listingblock">
<div class="title">MANIFEST.MF</div>
<div class="content">
<pre class="highlight"><code class="language-txt" data-lang="txt">Manifest-Version: 1.0
Bundle-ManifestVersion: 2
Bundle-Name: PetClinic HSQL Database Infrastructure
Bundle-SymbolicName: org.springframework.petclinic.infrastructure.hsqldb
Bundle-Version: 1.0
Import-Library: org.springframework.spring;version="[2.5,2.6]"
Import-Bundle: com.springsource.org.apache.commons.dbcp;version="[1.2.2.osgi,1.2.2.osgi]",
com.springsource.org.hsqldb;version="[1.8.0.9,1.8.0.9]"
Import-Package: javax.sql
Export-Package: org.springframework.petclinic.infrastructure</code></pre>
</div>
</div>
<div class="paragraph">
<p>The <code>org.springframework.petclinic.infrastructure.hsqldb</code> bundle expresses its dependencies on
the <code>javax.sql</code> package, the Commons DBCP and HSQLDB bundles, and the Spring library (we will examine
the details of the library artifact in <a href="#developing-applications-defining-libraries">Defining Libraries</a>. The Commons DBCP
bundle is imported at a version of exactly <code>1.2.2.osgi</code> and the HSQLDB bundle is imported at a version of exactly
<code>1.8.0.9</code>. The Spring library is imported at a version between <code>2.5</code> inclusive and <code>2.6</code> exclusive.</p>
</div>
<div class="paragraph">
<p>Note that you do not specify the bundle that will provide the imported packages.
Virgo will examine the available bundles and satisfy the required dependencies.</p>
</div>
<div class="paragraph">
<p>The following <code>osgi-context.xml</code> file from the PetClinic sample&#8217;s
<code>org.springframework.petclinic.repository.jdbc</code> bundle declares a service published by the bundle and
references a service published by another bundle.</p>
</div>
<div class="listingblock">
<div class="title">osgi-context.xml</div>
<div class="content">
<pre class="highlight"><code class="language-xml" data-lang="xml">&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;beans:beans xmlns="http://www.springframework.org/schema/osgi"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:beans="http://www.springframework.org/schema/beans"
xsi:schemaLocation="http://www.springframework.org/schema/osgi
http://www.springframework.org/schema/osgi/spring-osgi.xsd
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd"&gt;
&lt;service id="osgiClinic" ref="clinic" interface="org.springframework.petclinic.repository.Clinic" /&gt;
&lt;reference id="dataSource" interface="javax.sql.DataSource"/&gt;
&lt;/beans:beans&gt;</code></pre>
</div>
</div>
<div class="paragraph">
<p>The <code>service</code> element publishes the <code>clinic</code> bean
(a regular Spring bean declared in the <code>module-context.xml</code> file) and specifies
<code>org.springframework.petclinic.repository.Clinic</code> as the type
of the published service.</p>
</div>
<div class="paragraph">
<p>The <code>reference</code> elements define a <code>dataSource</code> bean that references
a service published by another bundle with a an interface type of <code>javax.sql.DataSource</code>.</p>
</div>
<div class="paragraph">
<p><a id="developing-applications-packaging"></a></p>
</div>
</div>
<div class="sect2">
<h3 id="_creating_pars_and_web_applications">Creating PARs and Web Applications</h3>
<div class="paragraph">
<p>Virgo supports two OSGi-oriented ways of packaging applications: the PAR format
and application bundles (including web bundles). The VTS also supports three
distinct WAR deployment and packaging formats: standard Java EE WAR, Shared Libraries WAR, Shared Services WAR.</p>
</div>
<div class="paragraph">
<p>Virgo also supports plans as a way to describe an application. This method is similar to a PAR
in that it encapsulates all the artifacts of an application as a single unit, but differs in that a plan simply
lists the bundles in an XML file rather than packaging all the bundles in a single JAR file. The use of plans
offers additional benefits to using PARs; for this reason, we recommend their use. For details, see
<a href="#developing-applications-plans">Creating Plans</a>.</p>
</div>
<div class="paragraph">
<p><a id="developing-applications-packaging-par"></a></p>
</div>
<div class="sect3">
<h4 id="_pars">PARs</h4>
<div class="paragraph">
<p>An OSGi application is packaged as a JAR file, with extension <code>.par</code>. A PAR artifact offers several benefits:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>A PAR file has an application name, version, symbolic name, and description.</p>
</li>
<li>
<p>The artifacts of a PAR file are scoped so that they cannot
be shared accidentally by other applications. The scope forms a boundary for automatic
propagation of load time weaving and bundle refresh.
See <a href="#developing-applications-plans-scoping">Plans and Scoping</a> for more on scoping.</p>
</li>
<li>
<p>Since a PAR is scoped, its artifacts have their exported packages imported by the
synthetic context bundle which is used for thread context class loading. So,
for example, hibernate will be able to load classes of any of the exported
packages of the bundles in a PAR file using the thread context class loader.</p>
</li>
<li>
<p>A PAR file is visible to management interfaces.</p>
</li>
<li>
<p>A PAR file can be undeployed and redeployed as a unit.</p>
</li>
<li>
<p>A PAR file is <strong>atomic</strong> in that it ties together the lifecycle of its artifacts. If you start, stop, or uninstall
one of a PAR&#8217;s artifacts, Virgo escalates the operation to the whole PAR file.
So Virgo prevents artifacts of a PAR from being in inconsistent states.
For example, if one artifact should fail to start, then Virgo stops all artifacts in the PAR.</p>
</li>
</ul>
</div>
<div class="paragraph">
<p>See <a href="#developing-applications-plans-scoping">Plans and Scoping</a> for more information on scoping.</p>
</div>
<div class="paragraph">
<p>A PAR includes one or more application bundles and its manifest specifies the following
manifest headers:</p>
</div>
<div class="paragraph">
<p><a id="developing-applications-packaging-par-headers-table"></a></p>
</div>
<table class="tableblock frame-all grid-all spread">
<caption class="title">Table 2. PAR file headers</caption>
<colgroup>
<col style="width: 50%;">
<col style="width: 50%;">
</colgroup>
<thead>
<tr>
<th class="tableblock halign-left valign-top">Header</th>
<th class="tableblock halign-left valign-top">Description</th>
</tr>
</thead>
<tbody>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>Application-SymbolicName</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Identifier for the application which, in combination with Application-Version, uniquely identifies an application</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>Application-Name</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Human readable name of the application</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>Application-Version</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Version of the application</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>Application-Description</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Short description of the application</p></td>
</tr>
</tbody>
</table>
<div class="paragraph">
<p>The following code shows an example MANIFEST.MF in a PAR file:</p>
</div>
<div class="listingblock">
<div class="title">MANIFEST.MF</div>
<div class="content">
<pre class="highlight"><code>Application-SymbolicName: com.example.shop
Application-Version: 1.0
Application-Name: Online Shop
Application-Description: Example.com's Online Shopping Application</code></pre>
</div>
</div>
<div class="paragraph">
<p>anchor:developing-applications-web-application-bundles</p>
</div>
</div>
<div class="sect3">
<h4 id="_web_application_bundles">Web Application Bundles</h4>
<div class="paragraph">
<p>Virgo for Apache Tomcat supports Web Application Bundles that are compliant with the OSGi Web Applications specification.
The defining property of a Bundle that makes it a Web Application Bundle is a manifest header, <code>Web-ContextPath</code>.
This defines the context path the web application will be registered under.</p>
</div>
<div class="paragraph">
<p>See <a href="#using-spring">Using Spring and Gemini Blueprint</a> for information on using Spring or Gemini Blueprint in a Web Application Bundle.</p>
</div>
<div class="paragraph">
<p><a id="developing-applications-plans"></a></p>
</div>
</div>
</div>
<div class="sect2">
<h3 id="_creating_plans">Creating Plans</h3>
<div class="paragraph">
<p>Plans are similar to PARs in that they encapsulate the artifacts of an application as a single unit.
However plans are XML files that refer to their artifacts, whereas PARs are JAR files that physically contain their artifacts.
Plans, known as <strong>parent</strong> plans may refer to other plans, known as <strong>child</strong> plans.</p>
</div>
<div class="paragraph">
<p>Plans share several benefits with PARs:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>A plan has a (symbolic) name and a version.</p>
</li>
<li>
<p>A plan may be <strong>scoped</strong>, although this is optional.
See <a href="#developing-applications-plans-scoping">Plans and Scoping</a> for more on scoping.</p>
</li>
<li>
<p>A plan is visible to management interfaces.</p>
</li>
<li>
<p>A plan can be undeployed and redeployed as a unit.</p>
</li>
<li>
<p>A plan may be <strong>atomic</strong>, although this is optional.</p>
</li>
</ul>
</div>
<div class="paragraph">
<p>Plans have the following additional benefits compared to PARs:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>Virgo deploys the artifacts in the plan in the order in which they are listed in the XML file, which gives you
complete control over deployment order.
With a PAR, the order of deployment of the included artifacts is not guaranteed.</p>
</li>
<li>
<p>Since plans refer to their artifacts, it is easier to share content between plans as well as update individual
parts of a plan without having to physically repackage (re-JAR) it.</p>
</li>
<li>
<p>Plans may contain child plans, but PARs cannot contain other PARs.</p>
</li>
<li>
<p>You can make certain plans deploy faster by disabling the provisioning of bundles to satisfy missing dependencies,
but you cannot disable provisioning for PARs.</p>
</li>
<li>
<p>You can specify whether a plan is scoped or unscoped and atomic or non-atomic; PARs are always scoped and atomic.</p>
</li>
</ul>
</div>
<div class="paragraph">
<p>The artifacts of a plan are usually stored in Virgo&#8217;s repository. This means, for example, that if you drop one of the plan&#8217;s artifacts in the <code>pickup</code> directory rather than adding it to the repository, the plan will fail to deploy because it will not find the artifact.</p>
</div>
<div class="paragraph">
<p>The artifacts of a plan may also be stored outside Virgo&#8217;s repository, somewhere else on the file system and referenced from the plan using URIs.
Such artifacts must be available on the file system when the plan is deployed and when Virgo restarts while the plan is deployed.
If you delete any of these artifacts, deployment of the plan may fail, either when it is initially deployed or when Virgo restarts.</p>
</div>
<div class="paragraph">
<p><a id="developing-applications-plans-create"></a></p>
</div>
<div class="sect3">
<h4 id="_creating_the_plan_xml_file">Creating the Plan XML File</h4>
<div class="paragraph">
<p>Plans are XML files that have a <code>.plan</code> file extension, such as <code>multi-artifact.plan</code>.
The structure of the XML file is simple:
the root element is <code>&lt;plan&gt;</code> with attributes specifying the name of the plan, the version, atomicity, and scoping.
Then, for each artifact that makes up your application,
you add a <code>&lt;artifact&gt;</code> element, using its attributes to specify the type of artifact and its name and version.
The following is a simple example of a plan&#8217;s XML file:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="highlight"><code class="language-xml" data-lang="xml">&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;plan name="multi-artifact.plan" version="1.0.0" scoped="true" atomic="true"
xmlns="http://www.eclipse.org/virgo/schema/plan"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.eclipse.org/virgo/schema/plan
http://www.eclipse.org/virgo/schema/plan/eclipse-virgo-plan.xsd"&gt;
&lt;artifact type="configuration" name="app-properties" version="1.0.0"/&gt;
&lt;artifact type="bundle" name="com.springsource.exciting.app" version="[2.0.0, 3.1.0)"/&gt;
&lt;/plan&gt;</code></pre>
</div>
</div>
<div class="paragraph">
<p>In the preceding example, the name of the plan is <code>multi-artifact.plan</code> and its version is <code>1.0.0</code>.
The plan is both scoped and atomic. The plan contains two artifacts: one is a bundle called <code>com.springsource.exciting.app</code> and the other is a configuration file called <code>app-properties</code>.</p>
</div>
<div class="paragraph">
<p>The following table describes the attributes of the <code>&lt;plan&gt;</code> element.</p>
</div>
<table class="tableblock frame-all grid-all spread">
<caption class="title">Table 3. PAR file headers</caption>
<colgroup>
<col style="width: 20%;">
<col style="width: 60%;">
<col style="width: 20%;">
</colgroup>
<thead>
<tr>
<th class="tableblock halign-left valign-top">Attribute</th>
<th class="tableblock halign-left valign-top">Description</th>
<th class="tableblock halign-left valign-top">Required?</th>
</tr>
</thead>
<tbody>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>name</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Specifies the name of this plan.
Virgo uses the name as one component of the unique
identifier of this plan.</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Yes.</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>version</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Specifies the version of this plan.
You must use OSGi version specification syntax,
such as <code>2.1.0</code>.
Virgo uses the version as one component of
the unique identifier of this plan.</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Yes.</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>scoped</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Specifies whether Virgo should install the
artifacts into plan-specific scope so that only the
application described by this plan has access to the artifacts.
If you disable scoping, then Virgo installs
the artifacts into the global scope, which means they
are then available for access by all other deployed artifacts.
Set the attribute to <code>true</code> to enable scoping or
<code>false</code> to disable it.</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Yes.</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>atomic</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Specifies whether you want to tie together the lifecycle
of the artifacts in this plan.
Making a plan atomic means that if you start, stop, or
uninstall a single artifact in the plan, Virgo
escalates the operation to the whole plan.
Also Virgo prevents artifacts of an atomic plan
from being in inconsistent states.
For example, if one artifact should fail to start,
then Virgo stops all artifacts in the plan.
Set this attribute to <code>true</code> to enable atomicity or
<code>false</code> to disable it.</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Yes.</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>provisioning</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Specifies whether Virgo installs bundles from
the repository to attempt to satisfy any missing
dependencies in the plan.
Missing dependencies prevent one or more bundles in
the plan from resolving.
For example, a bundle which imports a package cannot
resolve if the package is missing, that is, not
exported by another bundle. A value of
<code>auto</code> instructs Virgo to install bundles from the repository
to attempt to satisfy any missing dependencies in the plan.
This is known as <strong>auto-provisioning</strong>.
A value of <code>disabled</code> prevents Virgo from
installing bundles from the repository to attempt to
satisfy any missing dependencies in the plan.
This value can make the plan deploy faster, although if
there are missing dependencies, deployment will fail.
A value of <code>inherit</code>, which is the default if no value is specified, inherits the parent plan&#8217;s provisioning behaviour.
If the plan does not have a parent, it inherits Virgo&#8217;s
auto-provisioning behaviour.</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">No. If not specified, defaults to <code>inherit</code>.</p></td>
</tr>
</tbody>
</table>
<div class="paragraph">
<p>The following table describes the attributes of the <code>&lt;artifact&gt;</code> element. Note that you must either specify <code>type</code>, <code>name</code>, and (optionally) <code>version</code>,
in which case Virgo&#8217;s repository is searched for the artifact, or <code>uri</code> in which case the artifact is obtained directly from the file system.
If you specify <code>uri</code>, you must not specify <code>type</code>, <code>name</code>, or <code>version</code>.</p>
</div>
<div class="paragraph">
<p><a id="developing-applications-plans-create-artifact-attributes"></a></p>
</div>
<table class="tableblock frame-all grid-all spread">
<caption class="title">Table 4. PAR file headers</caption>
<colgroup>
<col style="width: 20%;">
<col style="width: 60%;">
<col style="width: 20%;">
</colgroup>
<thead>
<tr>
<th class="tableblock halign-left valign-top">Attribute</th>
<th class="tableblock halign-left valign-top">Description</th>
<th class="tableblock halign-left valign-top">Required?</th>
</tr>
</thead>
<tbody>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>type</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Specifies the type of the artifact. Valid values are:
</p><p class="tableblock"><code>bundle</code>: Specifies an OSGi bundle. Use this artifact type for WAR files and Web application bundles.
<code>configuration</code>: Specifies that the artifact is a configuration file. Configuration files contain name/value pairs that set initial values for configuration properties of a bundle.
<code>plan</code>: Specifies that the artifact is a plan.
<code>par</code>: Specifies that the artifact is a PAR.</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Yes, unless <code>uri</code> is specified in which case <code>type</code> must not be specified and is automatically determined from the artifact.</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>name</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Specifies the name of the artifact.
See <a href="#artifact-names">Artifact Names</a> for guidelines for determining
the name of an artifact.</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Yes, unless <code>uri</code> is specified in which case <code>name</code> must not be specified and is automatically determined from the artifact.</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>version</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Specifies the range of versions of this artifact that
Virgo should look up in its repositories and
then install and deploy.
You must use OSGi version specification syntax,
such as <code>[1.0.0, 2.0.0)</code>.
Note that a single version number represents the range
from that version number upwards.
For example, <code>1.3</code> represents the range of versions
greater than or equal to <code>1.3</code>.</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">No. If <code>uri</code> is specified, <code>version</code> must not be specified.
If neither <code>uri</code> nor <code>version</code> are specified, <code>version</code> defaults to <code>0</code>, which in OSGi means 0 to infinity, or any version.</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>uri</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Specifies an optional, absolute URI string beginning
with <code>file:</code> that refers to the artifact on the file system.
Such an artifact must be available on the file system
when the plan is deployed and when Virgo restarts
while the plan is deployed.
If you delete such an artifact, deployment of the plan may fail,
either when it is initially deployed or when Virgo restarts.
This attribute is normally omitted so that the artifact
is searched for in Virgo&#8217;s repository.</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">No. If not specified, Virgo searches for the artifact in its repository.</p></td>
</tr>
</tbody>
</table>
<div class="paragraph">
<p><a id="artifact-names"></a></p>
</div>
</div>
<div class="sect3">
<h4 id="_artifact_names">Artifact Names</h4>
<div class="paragraph">
<p>When you create a plan, you use the <code>name</code> attribute of the <code>&lt;artifact&gt;</code> element to specify the name of all the plan&#8217;s dependencies. This section describes how to determine the name of an artifact, which is not always obvious.</p>
</div>
<div class="paragraph">
<p>Use the following guidelines to determine the name of an artifact:</p>
</div>
<div class="ulist">
<ul>
<li>
<p><strong>Bundle</strong>: In this context, a <strong>bundle</strong> refers to a standard OSGi bundle as well as a Web Application Bundle and a WAR file. The name of a bundle is the value of the <code>Bundle-SymbolicName</code> header in the <code>META-INF/MANIFEST.MF</code> file of the <code>*.jar</code>.
If a WAR file has <code>Bundle-SymbolicName</code> header then it will be treated as a Web Application Bundle. The following <code>MANIFEST.MF</code> snippet shows a bundle with name <code>com.springsource.exciting.app</code>:</p>
</li>
</ul>
</div>
<div class="literalblock">
<div class="content">
<pre>Bundle-SymbolicName: org.eclispe.virgo.exciting.app</pre>
</div>
</div>
<div class="paragraph">
<p>If the bundle does not contain a <code>META-INF/MANIFEST.MF</code> file or the <code>MANIFEST.MF</code> doesn&#8217;t contain a <code>Bundle-SymbolicName</code> header, then the name of the bundle is its filename minus the <code>.jar</code> or <code>.war</code> extension.</p>
</div>
<div class="ulist">
<ul>
<li>
<p><strong>Configuration File</strong>: The name of a configuration or PID (Persistent Identity) is its filename minus the <code>.properties</code> extension. The PID can also be specified within the properties file with the
<strong>service.pid</strong> property.</p>
</li>
<li>
<p><strong>Plan</strong>: The name of a plan is the value of the required <code>name</code> attribute of the <code>&lt;plan&gt;</code> element in the plan&#8217;s XML file. In the following XML snippet, the plan name is <code>multi-artifact.plan</code>:</p>
</li>
</ul>
</div>
<div class="literalblock">
<div class="content">
<pre>&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;plan name="multi-artifact.plan" version="1.0.0" scoped="true" atomic="true"
xmlns="http://www.eclipse.org/virgo/schema/plan"&gt;</pre>
</div>
</div>
<div class="ulist">
<ul>
<li>
<p><strong>PAR</strong>: The name of a PAR is the value of the <code>Application-SymbolicName</code> header in the <code>META-INF/MANIFEST.MF</code> file of the <code>*.par</code> file. The following <code>MANIFEST.MF</code> snippet shows a PAR with name <code>com.springsource.my.par</code>:</p>
</li>
</ul>
</div>
<div class="literalblock">
<div class="content">
<pre>Application-SymbolicName: org.eclipse.virgo.my.par</pre>
</div>
</div>
<div class="paragraph">
<p>If the PAR does not contain a <code>META-INF/MANIFEST.MF</code> file, then the name of the PAR is its filename minus the <code>.par</code> extension.</p>
</div>
<div class="paragraph">
<p><a id="passing-properties"></a></p>
</div>
</div>
<div class="sect3">
<h4 id="_supplying_properties_to_artifacts">Supplying Properties to Artifacts</h4>
<div class="paragraph">
<p>It is possible to pass properties to an artifact specified in a plan. An example of this can be seen in the Admin Console plan where the context path to be used in the Admin console is passed from the plan.</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="highlight"><code class="language-xml" data-lang="xml">&lt;artifact type="bundle" name="org.eclipse.virgo.apps.admin.web" version="[3.0, 4.0)"&gt;
&lt;property name="header:Web-ContextPath" value="/admin" /&gt;
&lt;/artifact&gt;</code></pre>
</div>
</div>
<div class="paragraph">
<p>The only supported property is <code>header</code> which will overwrite the given manifest header with the supplied value. This should be used with care!</p>
</div>
<div class="paragraph">
<p><a id="developing-applications-plans-use"></a></p>
</div>
</div>
<div class="sect3">
<h4 id="_using_the_plan">Using the Plan</h4>
<div class="paragraph">
<p>Because a plan is a list of artifacts, rather than a physical file that contains the artifacts, there are a few additional steps you must perform before you deploy it to Virgo.</p>
</div>
<div class="olist arabic">
<ol class="arabic">
<li>
<p>Copy the artifacts that make up the plan to the <code>usr</code> repository, which by default is the <code>$SERVER_HOME/repository/usr</code> directory, where <code>$SERVER_HOME</code> refers to the top-level installation directory of Virgo. Note that you might have configured the server differently; in which case, copy the artifacts to your custom repository directory.</p>
</li>
<li>
<p>Restart Virgo if the repository used is not a <strong>watched</strong> repository.</p>
</li>
<li>
<p>After the server has started, either use the Admin Console to deploy the plan, or manually deploy it by copying the plan&#8217;s XML file into the <code>$SERVER_HOME/pickup</code> directory.</p>
</li>
<li>
<p>This results in Virgo deploying the plan.</p>
</li>
<li>
<p>To undeploy the plan, use the Admin Console, or simply delete it from the <code>$SERVER_HOME/pickup</code> directory.</p>
</li>
</ol>
</div>
<div class="paragraph">
<p><a id="developing-applications-plans-scoping"></a></p>
</div>
</div>
<div class="sect3">
<h4 id="_plans_and_scoping">Plans and Scoping</h4>
<div class="paragraph">
<p>As described in previous sections, you can specify that a plan be <strong>scoped</strong>. This means that Virgo installs the artifacts that make up the plan into a plan-specific scope so that only the application described by the plan has access to the artifacts. If you disable scoping, then Virgo installs the artifacts into the global scope, which means they are available for access by all other deployed artifacts. This section describes scoping in a bit more detail. It also describes how you can change the default behavior of scoping, with respect to services, so that a service that is in a scope can be made globally available.</p>
</div>
<div class="paragraph">
<p>If a bundle in a given scope imports a package and a bundle in the same scope exports the package, then the import may only be satisfied by the bundle in the scope, and not by any bundles outside the scope, including the global scope. Similarly, package exports from bundles in a scope are not visible to bundles in the global scope.</p>
</div>
<div class="paragraph">
<p>If a bundle in a scope uses Spring DM (or the blueprint service) to obtain a service reference and a bundle in the same scope uses Spring DM (or the blueprint service) to publish a matching service, then the service reference may only bind to the service published in the scope (and not to any services outside the scope). Services published by bundles in a scope are not visible to bundles in the global scope.</p>
</div>
<div class="paragraph">
<p>However, sometimes it is useful to make a service in a scope globally available to artifacts outside the scope. To do this, publish the service with the <code>org.eclipse.virgo.service.scope</code> service property set to <code>global</code>. Use the <code>&lt;service-properties&gt;</code> child element of <code>&lt;service&gt;</code>, as shown in the following example:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="highlight"><code class="language-xml" data-lang="xml">&lt;service id="publishIntoGlobal" interface="java.lang.CharSequence"&gt;
&lt;service-properties&gt;
&lt;beans:entry key="org.eclipse.virgo.service.scope" value="global" /&gt;
&lt;/service-properties&gt;
&lt;beans:bean class="java.lang.String"&gt;
&lt;beans:constructor-arg value="foo"/&gt;
&lt;/beans:bean&gt;
&lt;/service&gt;</code></pre>
</div>
</div>
<div class="paragraph">
<p>A scope forms a boundary for automatic propagation of load time weaving and bundle refresh.
Additionally, a synthetic context bundle is generated for each scope. This bundle imports all the packages exported by other bundles in the scope.
The class loader of the synthetic context bundle is used for thread context class loading. So,
for example, hibernate will be able to load classes of any of the exported
packages of the bundles in a scope using the thread context class loader.</p>
</div>
<div class="paragraph">
<p>To ensure predictable class loading behaviour and avoid other issues associated with <strong>split packages</strong> (packages whose classes
are split across more than one bundle), the synthetic context bundle has a restriction:
no package may be exported by more than one
bundle in the scope*.
If this restriction is broken, the scoped application will fail to deploy.
This restriction can cause problems for <a href="#scoping-and-substitutable-exports">substitutable exports</a>.</p>
</div>
<div class="paragraph">
<p><a id="developing-applications-plans-scoping-webapps"></a></p>
</div>
</div>
<div class="sect3">
<h4 id="_web_applications_and_scoping">Web Applications and Scoping</h4>
<div class="paragraph">
<p>A Web Application Bundle (WAB) or WAR has its bundle class loader set as the TCCL, even when the WAB or WAR belongs to
a PAR or scoped plan.
To enable the TCCL to load classes of other bundles in the same scope as a WAB or WAR, use a WAB which imports the necessary packages.</p>
</div>
<div class="paragraph">
<p>Also a WAB or WAR has its own per-application trace, independent of the per-application trace of any PAR or scoped plan to which the
WAB or WAR belongs.</p>
</div>
<div class="paragraph">
<p><a id="developing-applications-configuration-artifacts"></a></p>
</div>
</div>
</div>
<div class="sect2">
<h3 id="_creating_and_using_configuration_artifacts">Creating and Using Configuration Artifacts</h3>
<div class="paragraph">
<p>Applications typically include some sort of configuration data
that might change depending on the environment in which the
application is deployed. For example, if an application connects to a
database server using JDBC, the configuration data would include the
JDBC URL of the database server, the JDBC drvier, and the username and
password that the application uses to connect to the database server.
This information often changes as the application is deployed to
different computers or the application moves from the testing phase to
the production phase.</p>
</div>
<div class="paragraph">
<p>Virgo provides a feature called
<strong>configuration artifacts</strong>
that makes it very easy for you to manage this configuration data. A
configuration artifact is simply a properties file that is made
available at runtime using the OSGi
<code>ConfigurationAdmin</code>
service. When you create this properties file, you set the values of
the properties for the specific environment in which you are going to
deploy your application, and then update the metadata of your Spring
application to use the properties file. You then deploy the
application and properties file together, typically as a
<a href="#developing-applications-plans">plan</a>. Virgo automatically creates a configuration artifact from
the properties file, and you can manage the lifecycle of this
configuration artifact in the same way you manage the lifecycle of
PARs, bundles, and plans, using the Admin
Console. Additionally, Virgo subscribes your
application for notification of any refresh of the configuration
artifact and the application can then adapt accordingly, which means
you can easily
<strong>change</strong>
the configuration of your application without redeploying it.</p>
</div>
<div class="paragraph">
<p>In sum, configuration artifacts, especially when combined with
plans, provide an excellent mechanism for managing external
configuration data for your applications.</p>
</div>
<div class="paragraph">
<p>The following sections describe the format of the configuration
artifact, how to update the Spring application context file of your
application so that it knows about the configuration artifact, and
finally how to include it in a plan alongside your application.</p>
</div>
<div class="paragraph">
<p>As an example to illustrate the configuration artifact feature, assume
that you have a Spring bean called
<code>PropertiesController</code>
whose constructor requires that four property values be passed to it,
as shown in the following snippet of Java code:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="highlight"><code class="language-java" data-lang="java">@Controller
public class PropertiesController {
private final String driverClassName;
private final String url;
private final String username;
private final String password;
public PropertiesController(String driverClassName, String url, String username, String password) {
this.driverClassName = driverClassName;
this.url = url;
this.username = username;
this.password = password;
}</code></pre>
</div>
</div>
<div class="paragraph">
<p>In the preceding example, the <code>PropertiesController</code> constructor requires four property values: <code>driverClassName</code>, <code>url</code>, <code>username</code>, and <code>password</code>. Note that the example shows just one way that a class might require property values; your application may code it another way.</p>
</div>
<div class="paragraph">
<p>Additionally, assume that the following snippet of the associated Spring application context XML file shows how the <code>PropertiesController</code> bean is configured:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="highlight"><code class="language-xml" data-lang="xml">&lt;bean class="com.springsource.configuration.properties.PropertiesController"&gt;
&lt;constructor-arg value="${driverClassName}"/&gt;
&lt;constructor-arg value="${url}"/&gt;
&lt;constructor-arg value="${username}"/&gt;
&lt;constructor-arg value="${password}"/&gt;
&lt;/bean&gt;</code></pre>
</div>
</div>
<div class="paragraph">
<p>The rest of this section describes how the bean can get these property values using a configuration artifact.</p>
</div>
<div class="paragraph">
<p><a id="developing-applications-configuration-artifacts-propfile"></a></p>
</div>
<div class="sect3">
<h4 id="_creating_the_properties_file">Creating the Properties File</h4>
<div class="paragraph">
<p>To create a properties file that in turn will become a configuration artifact when deployed to Virgo from which a Spring bean, such as the <code>PropertiesController</code> bean, will get the actual property values, follow these guidelines:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>Create a text file in which each property is listed as a name/value pair, one pair per line. Precede comments with a <code>#</code>. For example:</p>
</li>
</ul>
</div>
<div class="literalblock">
<div class="content">
<pre># Properties for the com.springsource.configuration.properties sample
driverClassName = org.w3.Driver
url = http://www.springsource.com
username = joe
password = secret</pre>
</div>
</div>
<div class="paragraph">
<p>The example shows four properties whose name correspond to the constructor arguments of the <code>PropertiesController</code> Spring bean.</p>
</div>
<div class="ulist">
<ul>
<li>
<p>Name the file anything you want, as long as it has a <code>.properties</code> extension, such as <code>app-properties.properties</code>.</p>
</li>
</ul>
</div>
<div class="paragraph">
<p><a id="developing-applications-configuration-artifacts-app"></a></p>
</div>
</div>
<div class="sect3">
<h4 id="_updating_your_application">Updating Your Application</h4>
<div class="paragraph">
<p>To update your application so that it "knows" about the configuration artifact, you update the application&#8217;s Spring application context XML file, typically located in the <code>WEB-INF</code> or <code>META-INF/spring</code> directories (read <a href="#using-spring">Using Spring and Gemini Blueprint</a>
to understand which directory to use).</p>
</div>
<div class="paragraph">
<p>You use the <code>&lt;context:property-placeholder&gt;</code> element to specify that you want to use the Virgo mechanism for substituting values into bean properties. The <code>properties-ref</code> attribute of this element points to a <code>&lt;osgi-compendium:cm-properties&gt;</code> element which you use to specify the configuration artifact that contains the property values. You set the value of the <code>persistent-id</code> attribute of this element equal to the name of the configuration artifact, which is the name of the properties file <strong>minus</strong> the <code>.properties</code> extension.</p>
</div>
<div class="paragraph">
<p>The following sample Spring application context XMl file shows everything wired together; only relevant parts of the file are shown:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="highlight"><code class="language-xml" data-lang="xml">&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:osgi-compendium="http://www.springframework.org/schema/osgi-compendium"
xsi:schemaLocation="http://www.springframework.org/schema/osgi
http://www.springframework.org/schema/osgi/spring-osgi-1.2.xsd
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-2.5.xsd
http://www.springframework.org/schema/osgi-compendium
http://www.springframework.org/schema/osgi-compendium/spring-osgi-compendium-1.2.xsd"&gt;
...
&lt;bean class="com.springsource.configuration.properties.PropertiesController"&gt;
&lt;constructor-arg value="${driverClassName}"/&gt;
&lt;constructor-arg value="${url}"/&gt;
&lt;constructor-arg value="${username}"/&gt;
&lt;constructor-arg value="${password}"/&gt;
&lt;/bean&gt;
&lt;context:property-placeholder properties-ref="configAdminProperties"/&gt;
&lt;osgi-compendium:cm-properties id="configAdminProperties" persistent-id="app-properties"/&gt;
...
&lt;/beans&gt;</code></pre>
</div>
</div>
<div class="paragraph">
<p>The preceding example shows how the id <code>configAdminProperites</code> wires the <code>&lt;context:property-placeholder&gt;</code> and <code>&lt;osgi-compendium:cm-properties&gt;</code> elements together. Based on the value of the <code>persistent-id</code> attribute, you must also deploy a properties file called <code>app-properties.properties</code> which Virgo installs as a configuration artifact.</p>
</div>
<div class="paragraph">
<p><a id="developing-applications-configuration-artifacts-plan"></a></p>
</div>
</div>
<div class="sect3">
<h4 id="_adding_the_configuration_artifact_to_a_plan">Adding the Configuration Artifact to a Plan</h4>
<div class="paragraph">
<p>Although you can always deploy your application and associated configuration artifact using the <code>pickup</code> directory, we recommends that you group the two together in a plan, add the two artifacts to the repository, and then deploy the plan using the <code>pickup</code> directory. The following sample plan includes the two artifacts:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="highlight"><code class="language-xml" data-lang="xml">&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;plan name="multi-artifact.plan" version="1.0.0"
scoped="false" atomic="false"
xmlns="http://www.eclipse.org/virgo/schema/plan"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.eclipse.org/virgo/schema/plan
http://www.eclipse.org/virgo/schema/plan/eclipse-virgo-plan.xsd"&gt;
&lt;artifact type="configuration" name="app-properties" version="0"/&gt;
&lt;artifact type="bundle" name="org.eclipse.virgo.configuration.properties" version="1.0.0"/&gt;
&lt;/plan&gt;</code></pre>
</div>
</div>
<div class="paragraph">
<p>For additional information about plans, see <a href="#developing-applications-plans">Creating Plans</a>.</p>
</div>
<div class="paragraph">
<p><a id="using-spring"></a></p>
</div>
</div>
</div>
<div class="sect2">
<h3 id="_using_spring_and_gemini_blueprint">Using Spring and Gemini Blueprint</h3>
<div class="paragraph">
<p>Virgo supports the use of Spring framework and Gemini Blueprint by application bundles.</p>
</div>
<div class="paragraph">
<p>Spring (and Gemini Blueprint) application context XML files should generally be placed in a bundle&#8217;s <code>META-INF/spring</code> directory, but
for a web application, these files must be placed in the <code>WEB-INF</code> directory.</p>
</div>
<div class="admonitionblock tip">
<table>
<tr>
<td class="icon">
<div class="title">Tip</div>
</td>
<td class="content">
<div class="title">A common mistake</div>
<div class="paragraph">
<p>Placing a web application&#8217;s Spring application context XML files in the <code>META-INF/spring</code> directory produces
unpredictable results since Spring DM will attempt to build an application context independently of, and asynchronously from,
the web application.</p>
</div>
</td>
</tr>
</table>
</div>
<div class="paragraph">
<p>To use Gemini Blueprint from a web application, the <code>contextClass</code> servlet parameter and the servlet context listener
should be configured (in <code>WEB-INF/web.xml</code>) like this:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="highlight"><code class="language-xml" data-lang="xml">&lt;context-param&gt;
&lt;param-name&gt;contextClass&lt;/param-name&gt;
&lt;param-value&gt;org.eclipse.virgo.web.dm.ServerOsgiBundleXmlWebApplicationContext&lt;/param-value&gt;
&lt;/context-param&gt;
&lt;listener&gt;
&lt;listener-class&gt;org.springframework.web.context.ContextLoaderListener&lt;/listener-class&gt;
&lt;/listener&gt;</code></pre>
</div>
</div>
<div class="paragraph">
<p>Virgo has Gemini Blueprint built-in and thereby supports the OSGi Blueprint standard in addition to Spring DM.</p>
</div>
<div class="paragraph">
<p>For detailed information on Spring Framework and Blueprint, please see <a href="#prerequisites-references">Prerequisites</a>.</p>
</div>
<div class="paragraph">
<p><a id="developing-applications-programmatic-access"></a></p>
</div>
</div>
<div class="sect2">
<h3 id="_programmatic_access_to_the_servlet_context">Programmatic Access to the Servlet Context</h3>
<div class="paragraph">
<p>This section describes how to programmatically access the servlet context to obtain the WebApplicationContext or the BundleContext.</p>
</div>
<div class="paragraph">
<p><a id="developing-applications-programmatic-access-web"></a></p>
</div>
<div class="sect3">
<h4 id="_programmatic_access_to_web_features">Programmatic Access to Web Features</h4>
<div class="paragraph">
<p><a id="developing-applications-programmatic-access-web-application-context"></a></p>
</div>
</div>
<div class="sect3">
<h4 id="_programmatic_access_to_the_webapplicationcontext">Programmatic Access to the WebApplicationContext</h4>
<div class="paragraph">
<p>The Virgo for Apache Tomcat automatically creates a <code>WebApplicationContext</code>
for Web Application Bundles and WAR files. When used in conjunction with an
an auto-configured Spring MVC <code>DispatcherServlet</code>,
there is generally no need to access the <code>WebApplicationContext</code>
programmatically, since all components of the web application are configured
within the scope of the <code>WebApplicationContext</code>
itself. However, if you wish to access the <code>WebApplicationContext</code>
you can do so via the web application&#8217;s <code>ServletContext</code>.
Virgo stores the bundle&#8217;s
<code>WebApplicationContext</code> in the ServletContext under
the attribute name &#8220;BSN-ApplicationContext&#8221;, where
<code>BSN</code> is the <code>Bundle-SymbolicName</code>
of your WAR or Web Application Bundle.</p>
</div>
<div class="paragraph">
<p>Alternatively, since Virgo also stores the
<code>WebApplicationContext</code> under the attribute name
with the value of the <code>WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE</code>
constant, you may choose to use Spring MVC&#8217;s WebApplicationContextUtils'
<code>getWebApplicationContext(servletContext)</code>
or
<code>getRequiredWebApplicationContext(servletContext)</code>
methods to access the <code>WebApplicationContext</code> without providing
an explicit attribute name.</p>
</div>
<div class="paragraph">
<p><a id="developing-applications-programmatic-access-web-bundle-context"></a></p>
</div>
</div>
<div class="sect3">
<h4 id="_programmatic_access_to_the_bundlecontext">Programmatic Access to the BundleContext</h4>
<div class="paragraph">
<p>As required by the OSGi Web Applications specification, you can access the
<code>BundleContext</code> of your WAR or Web Application Bundle via the web application&#8217;s
<code>ServletContext</code>. The bundle context is stored in the
<code>ServletContext</code> under the attribute name <code>osgi-bundlecontext</code>.</p>
</div>
<div class="paragraph">
<p><a id="developing-applications-automatic-imports-web"></a></p>
</div>
</div>
</div>
<div class="sect2">
<h3 id="_web_application_manifest_processing">Web Application Manifest Processing</h3>
<div class="paragraph">
<p>Virgo for Apache Tomcat generates automatic package imports (i.e., via the
<code>Import-Package</code> manifest header) for certain web applications.
This section lists which packages are automatically generated.</p>
</div>
<div class="paragraph">
<p>VTS supports Web Application Bundles (WABs) as defined by the OSGi Web Applications Specification and WAR files.
A WAR will typically not contain any OSGi defined manifest headers.
A WAB is distinguished from a WAR by the presence of one or more of the following OSGi defined headers:</p>
</div>
<div class="ulist">
<ul>
<li>
<p><code>Bundle-SymbolicName</code></p>
</li>
<li>
<p><code>Bundle-Version</code></p>
</li>
<li>
<p><code>Bundle-ManifestVersion</code></p>
</li>
<li>
<p><code>Import-Package</code></p>
</li>
<li>
<p><code>Web-ContextPath</code></p>
</li>
</ul>
</div>
<div class="paragraph">
<p>As required by the OSGi Web Applications specification, the following defaults are applied to a WAR:</p>
</div>
<div class="ulist">
<ul>
<li>
<p><code>Bundle-ManifestVersion</code> is set to <code>2</code></p>
</li>
<li>
<p><code>Bundle-SymbolicName</code> is generated from the path from which the bundle was installed</p>
</li>
<li>
<p><code>Bundle-ClassPath</code> is set to <code>WEB-INF/classes</code> followed by the JARs in
<code>WEB-INF/lib</code> in an unspecified order, followed by any transitive dependencies declared
by the JARs in <code>WEB-INF/lib</code></p>
</li>
<li>
<p><code>Import-Package</code> is extended in an implementation defined way, as described below</p>
</li>
</ul>
</div>
<div class="paragraph">
<p>The following packages are automatically imported into WARs:</p>
</div>
<div class="ulist">
<ul>
<li>
<p><code>javax.servlet;version="2.5"</code></p>
</li>
<li>
<p><code>javax.servlet.http;version="2.5"</code></p>
</li>
<li>
<p><code>javax.servlet.jsp;version="2.1"</code></p>
</li>
<li>
<p><code>javax.servlet.jsp.el;version="2.1"</code></p>
</li>
<li>
<p><code>javax.servlet.jsp.tagext;version="2.1"</code></p>
</li>
<li>
<p><code>javax.el;version="1.0"</code></p>
</li>
</ul>
</div>
<div class="paragraph">
<p>In addition to the above-described imports, VTS will also
generate automatic imports for all of the packages that are exported by the system
bundle, unless an import for the package already exists in the WAR&#8217;s manifest,
or the WAR contains the package, i.e. within <code>WEB-INF/classes</code>,
or in a jar file in <code>WEB-INF/lib</code>. When an import is generated, it
is versioned such that it exactly matches the version or versions of the package that
are exported from the system bundle. For example, a package that&#8217;s exported only at
version <code>1.0.0</code> will generate an import with a version of
<code>[1.0.0,1.0.0]</code>, and a package that&#8217;s exported at version
<code>1.0.0</code> and version <code>2.0.0</code> will generate an import
with a version of <code>[1.0.0,2.0.0]</code>.</p>
</div>
<div class="paragraph">
<p>Web Application Bundles are not subject to the above manifest processing.
This is a change of behaviour compared to Virgo Web Server 2.1.x.
See (see <a href="#known-issues-web-bundle-default-headers">Default Web
Application Bundle Headers</a>) if you need the old behaviour until you
have changed your WABs to match the new behaviour.</p>
</div>
<div class="paragraph">
<p>VTS supports ROOT.war as a default web application. The <code>Web-ContextPath</code>
of the deployed ROOT.war is set to the default web context path - <code>/</code>.</p>
</div>
<div class="admonitionblock tip">
<table>
<tr>
<td class="icon">
<div class="title">Tip</div>
</td>
<td class="content">
<div class="title">System Bundle Package Exports</div>
<div class="paragraph">
<p>For further details on which packages are exported by the
OSGi system bundle, consult the &lt;filename&gt;java-server.profile&lt;/filename&gt;
file located in the <code>SERVER_HOME/configuration</code> directory.</p>
</div>
</td>
</tr>
</table>
</div>
<div class="paragraph">
<p><a id="developing-applications-dependencies"></a></p>
</div>
</div>
<div class="sect2">
<h3 id="_working_with_dependencies">Working with Dependencies</h3>
<div class="paragraph">
<p>Complex enterprise frameworks such a Spring and Hibernate are typically divided into many, many different
packages. Traditionally, if an OSGi bundle wished to make extensive use of such a framework its manifest would
have to import a huge number of different packages. This can be an error-prone and tedious process. Furthermore,
application developers are used to thinking in terms of their application using a framework, such as Spring, as a
whole, rather than a long list of all the different packages that comprise the framework.</p>
</div>
<div class="paragraph">
<p>The following figure provides a simple illustration of the complexity of only using <code>Import-Package</code>:</p>
</div>
<div class="paragraph">
<p><span class="image"><img src="assets/images/import-package.png" alt="import package"></span></p>
</div>
<div class="paragraph">
<p>Virgo reduces the need for long lists of imported packages by introducing two new m