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| </script><!--End Google Analytics code--></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="book" lang="en"><div class="titlepage"><div><div><h1 class="title"><a name="d0e1"></a>Virgo Snaps User Guide</h1></div><div><div class="authorgroup"><div class="author"><h3 class="author"><span class="firstname">Christopher</span> <span class="surname">Frost</span></h3></div></div></div><div><div class="mediaobject" align="right"><img src="images/virgo-logo-small.png" align="right"></div></div><div><span class="productname">Virgo Snaps<br></span></div><div><p class="releaseinfo">3.6.3.RELEASE</p></div></div><div><div><div class="legalnotice"><a name="d0e22"></a><p> |
| Copyright © 2011 VMware Inc. |
| </p></div></div></div><hr></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="chapter"><a href="#introduction">1. Introduction</a></span></dt><dd><dl><dt><span class="section"><a href="#introduction-concepts">1.1. Concepts</a></span></dt><dt><span class="section"><a href="#introduction-prereqs">1.2. Prerequisites</a></span></dt></dl></dd><dt><span class="chapter"><a href="#installation">2. Installing Virgo Snaps</a></span></dt><dd><dl><dt><span class="section"><a href="#installation-zip">2.1. Installing from the Zip Download</a></span></dt><dt><span class="section"><a href="#installation-post">2.2. Verifying it's working</a></span></dt></dl></dd><dt><span class="chapter"><a href="#using-snaps">3. Using Virgo Snaps in your application</a></span></dt><dd><dl><dt><span class="section"><a href="#using-snaps-configuring-the-host">3.1. Configuring the Host</a></span></dt><dt><span class="section"><a href="#using-snaps-configuring-a-snap">3.2. Configuring a Snap</a></span></dt><dt><span class="section"><a href="#using-snaps-taglibs">3.3. Using the Snaps taglibs</a></span></dt><dt><span class="section"><a href="#using-snaps-host-prefix">3.4. Referencing Resources</a></span></dt></dl></dd><dt><span class="chapter"><a href="#sample-application">4. A Sample Application</a></span></dt><dd><dl><dt><span class="section"><a href="#sample-application-structure">4.1. Structure of the sample application</a></span></dt><dt><span class="section"><a href="#sample-application-host">4.2. The Host bundle</a></span></dt><dt><span class="section"><a href="#sample-application-new-content">4.3. Adding New Content</a></span></dt><dt><span class="section"><a href="#sample-application-dynamic-styling">4.4. Re-styling</a></span></dt></dl></dd><dt><span class="chapter"><a href="#further-reading">5. Further Reading</a></span></dt><dt><span class="chapter"><a href="#known-issues">6. Known Issues</a></span></dt><dd><dl><dt><span class="section"><a href="#known-issues-jetty-restriction">6.1. Virgo Jetty Server Restriction</a></span></dt></dl></dd></dl></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="introduction"></a>1. Introduction</h2></div></div></div><p> |
| This Guide covers Virgo Snaps and assumes you are already familiar with OSGi and Virgo. See <a class="link" href="#further-reading" title="5. Further Reading">here</a>. |
| </p><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="introduction-concepts"></a>1.1 Concepts</h2></div></div></div><p> |
| Using Virgo Snaps, or VS for short, you can construct a web application from multiple OSGi |
| bundles, each of which serves up content for a distinct sub-portion of your application's URL space. VS |
| applications are arranged in a parent/child structure, with each application having at most one top-level parent, and zero or more |
| children/grand children and so on. Parents are referred to as the hosts, children as snaps. |
| </p><p> |
| <img src="images/snapsAndHosts.png"> |
| </p><p> |
| Here you see that any <code class="literal">HTTP</code> requests for '/app' will be dealt with by the host bundle while '/app/orders' |
| and '/app/billing' will be dealt with by their respective snaps bundles. Each host/snap can use completely different web technologies |
| to deal with the requests, VS places no restrictions on your choices. The developer decides how to split |
| the application up and how closely to couple the host and various snaps. VS has been designed to be as |
| un-invasive as possible while still making it easy to share information between the host and its snaps. |
| </p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="introduction-prereqs"></a>1.2 Prerequisites</h2></div></div></div><p> |
| VS requires Virgo Tomcat Server and Java SE 6 or later to be installed. Java is available from |
| <a class="ulink" href="http://www.java.com/" target="_top">http://www.java.com/</a> and elsewhere. Virgo Tomcat Server is available from |
| <a class="ulink" href="http://www.eclipse.org/virgo/download/" target="_top">here</a>. |
| </p></div></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="installation"></a>2. Installing Virgo Snaps</h2></div></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="installation-zip"></a>2.1 Installing from the Zip Download</h2></div></div></div><p> |
| VS is distributed as a Zip file. This can be downloaded from |
| <a class="ulink" href="http://www.eclipse.org/virgo/download/" target="_top">here</a>. |
| </p><p> |
| Once the Zip file is unpacked you will find several things inside, including a copy of this documentation in the |
| <code class="literal">docs</code> folder. The layout is shown below. |
| </p><p> |
| </p><table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0" width="425"><tr><td align="center"><img src="images/snapsZipFile.png" align="middle" width="425"></td></tr></table><p> |
| </p><p> |
| Take the bundles and plan in the <code class="literal">dist</code> folder and place them in either the <code class="literal">/repository/usr</code> |
| or <code class="literal">/repository/ext</code> folder of your Virgo install. Later you need the bundles in the <code class="literal">sample</code> |
| folder. If you wish to view the source for VS or its sample, then these are in the <code class="literal">src</code> |
| folder. |
| </p><p> |
| In order to start the Snaps system as a part of your Virgo Tomcat Server, the Snaps plan needs to be referenced |
| from the <code class="literal">initialArtifacts</code> property. This is located in the config file at |
| <code class="literal">${SERVER_HOME}/config/org.eclipse.virgo.kernel.userregion.properties</code>. The property should be |
| extended like this. |
| </p><pre class="screen">initialArtifacts=repository:plan/org.eclipse.virgo.kernel.userregion.springdm, |
| repository:plan/org.eclipse.virgo.web.tomcat, |
| <span class="emphasis"><em>repository:plan/org.eclipse.virgo.snaps</em></span></pre><p> |
| Now you are ready to check that Snaps is working. |
| </p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="installation-post"></a>2.2 Verifying it's working</h2></div></div></div><p> |
| The sample application in the Zip file demonstrates all of the features of Snaps. You will cover this application in |
| detail later, but for now install it to verify that you have a working Snaps install. Start the server up and check |
| the output it produces contains the following: |
| </p><pre class="screen"><DE0004I> Starting plan 'org.eclipse.virgo.snaps' version '3.0.0'. |
| <DE0004I> Starting bundle 'org.eclipse.virgo.snaps.api' version '3.6.3.RELEASE'. |
| <DE0005I> Started bundle 'org.eclipse.virgo.snaps.api' version '3.6.3.RELEASE'. |
| <DE0004I> Starting bundle 'org.eclipse.virgo.snaps.core' version '3.6.3.RELEASE'. |
| <DE0005I> Started bundle 'org.eclipse.virgo.snaps.core' version '3.6.3.RELEASE'. |
| <DE0005I> Started plan 'org.eclipse.virgo.snaps' version '3.0.0'.</pre><p> |
| Open up the Virgo Admin Console by navigating to <code class="literal">http://localhost:8080/admin</code> and then go |
| to the artifacts tab to deploy some new bundles. The first bundle to deploy is located at |
| <code class="literal">/sample/org.eclipse.virgo.snaps.sample.animal-3.6.3.RELEASE.jar</code>, select it in the browser and |
| upload. In the terminal window you started the Virgo Tomcat Server in you should see the usual messages about the |
| bundle starting and this message: |
| </p><pre class="screen"><SN0000I> Host created for path '/animal-menu-bar'</pre><p> |
| This shows that the host has been registered and is ready for Snaps to attach to it. To view the application take |
| your browser to <code class="literal">http://localhost:8080/animal-menu-bar/</code>. You should be presented with a green looking |
| page that has a menu bar with two links on it. One will take you to the page you are currently on while the other goes |
| back to the admin page. |
| </p><p> |
| This is all very nice, but it's time to deploy another snap that will dynamicaly add some extra content to the app. The next bundle |
| to deploy is located at <code class="literal">/sample/org.eclipse.virgo.snaps.sample.dog-3.6.3.RELEASE.jar</code>. Deploy it the same way |
| as the last one using the admin console and check the messages to verify it has been bound to the host: |
| </p><pre class="screen"><SN0010I> Snap bound to path '/animal-menu-bar/dog' </pre><p> |
| In your browser, go back to the application and refresh the page and a new menu item should now be present. If you click it a new |
| page will load with content from the newly installed snap. In this case a picture of a dog. |
| </p><p> |
| <img src="images/sampleDog.png"> |
| </p><p> |
| You have now verified that your install is working and can continue on to learn how Snaps works and how you can use it to break up |
| your web applications. |
| </p></div></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="using-snaps"></a>3. Using Virgo Snaps in your application</h2></div></div></div><p> |
| Every snap or host should also be a regular WAB (Web Application Bundle), all you have to do is add some additional |
| configuration to benefit from VS. |
| </p><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="using-snaps-configuring-the-host"></a>3.1 Configuring the Host</h2></div></div></div><p> |
| In the WAB that is to act as a host to Snaps bundles, all that needs to be added is a filter in the hosts ' |
| <code class="literal">web.xml</code>'. This filter can be mapped to any sub path that you want forwarded to registered |
| snaps. It is important to note the extra <code class="literal">dispatcher</code> declarations in the <code class="literal">filter-mapping</code>. |
| Without these internal lookups, resources like JSPs won't get passed to the appropriate snap when needed. |
| </p><pre class="programlisting"> |
| <filter> |
| <filter-name>host-filter-name</filter-name> |
| <filter-class>org.eclipse.virgo.snaps.core.SnapHostFilter</filter-class> |
| </filter> |
| |
| <filter-mapping> |
| <filter-name>host-filter-name</filter-name> |
| <url-pattern>/*</url-pattern> |
| <dispatcher>INCLUDE</dispatcher> |
| <dispatcher>FORWARD</dispatcher> |
| <dispatcher>REQUEST</dispatcher> |
| </filter-mapping> |
| </pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="using-snaps-configuring-a-snap"></a>3.2 Configuring a Snap</h2></div></div></div><p> |
| A snap is a normal WAB with the addition of two extra manifest headers. The first <code class="literal">Snap-Host</code> is used |
| to resolve the WAB you want to act as a host for this snap. The second <code class="literal">Snap-ContextPath</code> gives the |
| path the snap will answer to. In order to reach the snap a request must be made for the host's context path, plus any |
| path in the host's Snaps filter followed by the path given with the <code class="literal">Snap-ContextPath</code> header. |
| </p><pre class="programlisting"> |
| Snap-Host: org.eclipse.virgo.snaps.sample.animal;version="${version:[=.=.=, =.+1)}" |
| Snap-ContextPath: /dog |
| </pre></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="using-snaps-taglibs"></a>3.3 Using the Snaps taglibs</h2></div></div></div><p> |
| There is a tag library available that makes information about the Snaps environment available to the host from within a |
| JSP page. The prefix and URI to declare are <code class="code"><%@ taglib prefix="snaps" uri="http://www.eclipse.org/virgo/snaps" |
| %></code>. You can now access an array of all the Snaps currently registered with the host. Each snap in the array |
| has two values, the first is the context path the Snap is registered with, as given in the snaps manifest header. The |
| second is an array of properties, if any, given in a property file in the snap. The file must be in the <code class="literal">META-INF |
| </code> directory and have a name of <code class="literal">snap.properties</code>. The following code snippet shows all of these |
| in use to produce links to each of the installed snaps. |
| </p><pre class="programlisting"> |
| <snaps:snaps var="snaps"> |
| <c:forEach var="snap" items="${snaps}"> |
| <a href="<c:url value="${snap.contextPath}${snap.properties['link.path']}"/>"> |
| ${snap.properties['link.text']}</a> |
| </c:forEach> |
| </snaps:snaps> |
| </pre><p> |
| The first line uses the Snaps tag library to place the array of snaps into the <code class="code">snaps</code> variable. Then a |
| <code class="code">forEach</code> loop goes through each snap. The content of the <code class="code">forEach</code> loop is the really interesting |
| bit. The first variable <code class="code">${snap.contextPath}</code> returns the context path of the snap. The two lookups are for |
| properties <code class="code">${snap.properties['something']}</code>. They rely on the snap having the properties file in place with |
| <code class="literal">link.path</code> and <code class="literal">link.text</code> defined in it. This shows the flexibility you have for defining |
| your own contract between the host and its snaps. In this case each snap can contribute extra information about how links in |
| a menu should be constructed. |
| </p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="using-snaps-host-prefix"></a>3.4 Referencing Resources</h2></div></div></div><p> |
| If the snap needs to lookup any resources, this can be done in the normal way and if the resource cannot be found in the snap, |
| then the host will be checked. Remember that a host and all its snaps use a single <code class="literal">ServletContext</code>. As the |
| snap is always checked first it can hide resources at the same path in its host. So if you want to look up a resource in the |
| snaps host that exists in the snap simply prefix the path with <code class="code">host:</code>. This will then cause the Snaps system to |
| bypass the snap and look only in its host for the requested resource. If it is not found in its host the snap will NOT be |
| checked, the lookup will return with nothing. |
| </p><pre class="programlisting"> |
| request.getServletContext().getResource("host:/WEB-INF/sample.properties"); |
| </pre><p> |
| </p><p> |
| This line of Java code gets the ServletContext from the HttpRequest object and then tries to get a resource from the host, |
| bypassing the snap. |
| </p><p> |
| </p></div></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="sample-application"></a>4. A Sample Application</h2></div></div></div><p> |
| The Virgo Snaps Zip file comes with a sample application that you may have already deployed to verify |
| your VS install. In this chapter you will look at it in more detail to see how an |
| application can be composed and see all the Snaps features in action. |
| </p><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="sample-application-structure"></a>4.1 Structure of the sample application</h2></div></div></div><p> |
| The application is very simple, it consists of just a front end, composed of four bundles, a host with |
| three Snaps. |
| </p><p> |
| <img src="images/sampleApp.png"> |
| </p><p> |
| The host and three snaps show their <code class="literal">Snap-ContextPath</code>s. The Cat and Dog snaps both |
| contribute content while the final snap just contributes styling information in the form of <code class="literal">css</code> |
| files. The following sections look at each of these in detail. |
| </p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="sample-application-host"></a>4.2 The Host bundle</h2></div></div></div><p> |
| This bundle is very simple with no Java code. It defines the Snaps filter in its <code class="literal">web.xml</code> |
| just as you have seen in the <a class="link" href="#using-snaps-configuring-the-host" title="3.1 Configuring the Host">Using Snaps</a> section. The |
| menu bar uses the taglibs support to render links for each registered Snap. |
| </p><pre class="programlisting"> |
| <ul> |
| <li><a href="<c:url value="/"/>">Home</a></li> |
| <snaps:snaps var="snaps"> |
| <c:forEach var="snap" items="${snaps}"> |
| <c:if test="${snap.contextPath ne '/styles'}"> |
| <li><a href="<c:url value="${snap.contextPath}${snap.properties['link.path']}"/>"> |
| ${snap.properties['link.text']}</a> |
| </li> |
| </c:if> |
| </c:forEach> |
| </snaps:snaps> |
| </ul> |
| </pre><p> |
| This is very similar to an example you have already seen. It puts the links in a list and adds a link at the |
| beginning to return to the host. The properties it is referencing are located in the snaps themselves at |
| <code class="literal">/META-INF/snap.properties</code>. |
| </p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="sample-application-new-content"></a>4.3 Adding New Content</h2></div></div></div><p> |
| If you now deploy both the Dog and Cat snaps, two new items will appear on the menu bar, each providing content |
| from their respective snaps. |
| </p><p> |
| <img src="images/sampleCat.png"> |
| </p><p> |
| If you look at the Cat page you will see it is also displaying some properties. The Cat Snap is a little more |
| complex, it has it's own <code class="literal">DispatcherServlet</code> defined in its <code class="literal">web.xml</code> and a |
| controller defined using annotations. If you look at the controller code you will see where these two properties |
| come from. |
| </p><pre class="programlisting"> |
| @Controller |
| public class CatController { |
| |
| @RequestMapping("/meow") |
| public ModelAndView cat(HttpServletRequest request) throws IOException { |
| URL host = request.getServletContext().getResource("host:/WEB-INF/sample.properties"); |
| Properties host_props = new Properties(); |
| if(host != null){ |
| host_props.load(host.openStream()); |
| } |
| URL snap = request.getServletContext().getResource("/WEB-INF/sample.properties"); |
| Properties snap_props = new Properties(); |
| if(snap != null){ |
| snap_props.load(snap.openStream()); |
| } |
| return new ModelAndView("index").addObject("host", host_props.getProperty("some.property")) |
| .addObject("snap", snap_props.getProperty("some.property")); |
| } |
| } |
| </pre><p> |
| There are two properties files called <code class="literal">sample.properties</code> located at the same path within both |
| the Cat snap and the host. Each contains a property called <code class="literal">some.property</code> but with distinct |
| value. Looking at the code above you can see the <code class="code">host:</code> prefix being used to ensure the first lookup |
| only looks in the host and skips the snap. These values are then placed in the Model for the JSP page to render. |
| </p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="sample-application-dynamic-styling"></a>4.4 Re-styling</h2></div></div></div><p> |
| Finally the Blue styling snap shows how Snaps can be used in other ways. Deploying this will cause all requests |
| to <code class="literal">/styles</code> to be redirected and the application will change in appearance but not content. All |
| this happens without re-deploying the host bundle, although you may need to do a full refresh to clear your browser's |
| cache. |
| </p><p> |
| <img src="images/sampleBlue.png"> |
| </p> |
| This is the same page as before, being rendered by the host and the Cat snap, but with the style information now coming |
| from the Blue snap. |
| </div></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="further-reading"></a>5. Further Reading</h2></div></div></div><p> |
| The User and Programmer Guides provide a lot of information about using and developing applications for the Virgo Server. |
| </p><p> |
| <a class="ulink" href="http://www.eclipse.org/virgo/documentation/" target="_top"> |
| Virgo Documentation page |
| </a> |
| </p><p> |
| <a class="ulink" href="../../virgo-programmer-guide/html/index.html" target="_top"> |
| Virgo Tomcat Server Programmer Guide |
| </a> |
| </p><p> |
| <a class="ulink" href="../../virgo-user-guide/html/index.html" target="_top"> |
| Virgo Tomcat Server User Guide |
| </a> |
| </p><p> |
| <a class="ulink" href="http://www.slideshare.net/cgfrost/eclipsecon2011-virgo-snaps" target="_top"> |
| Slides from a presentation at EclipseCon 2011 about Virgo Snaps. |
| </a> |
| </p></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="known-issues"></a>6. Known Issues</h2></div></div></div><p> |
| This section describes known issues that you might run into, along with corresponding workarounds. |
| </p><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="known-issues-jetty-restriction"></a>6.1 Virgo Jetty Server Restriction</h2></div></div></div><p> |
| Virgo Snaps is not supported on the Virgo Jetty Server, please use with the Virgo Tomcat Server. |
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