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| </head> |
| <body class="article"> |
| <div id="header"> |
| <h1>Virgo Snaps User Guide</h1> |
| <div class="details"> |
| <span id="author" class="author">Daniel Marthaler</span><br> |
| <span id="revdate">2017-02-04</span> |
| </div> |
| </div> |
| <div id="content"> |
| <div id="preamble"> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>Christopher Frost<br> |
| Daniel Marthaler</p> |
| </div> |
| <div class="paragraph"> |
| <p><strong>Virgo Snaps 3.7.1.SNAPSHOT</strong> <span class="image" style="float: right"><img src="images/virgo-logo-large.png" alt="Eclipse Virgo" width="300"></span></p> |
| </div> |
| <div class="paragraph"> |
| <p>VMware Inc. - initial contribution<br> |
| Copyright © 2009, 2011 VMware Inc. and others</p> |
| </div> |
| <hr> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="introduction">1. Introduction</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>This Guide covers Virgo Snaps and assumes you are already |
| familiar with OSGi and Eclipse Virgo. See <a href="#further-reading">here</a>.</p> |
| </div> |
| <div class="sect2"> |
| <h3 id="introduction-concepts">1.1. Concepts</h3> |
| <div class="paragraph"> |
| <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> |
| </div> |
| <div class="imageblock"> |
| <div class="content"> |
| <img src="images/snapsAndHosts.png" alt="snapsAndHosts"> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Here you see that any <code>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, |
| Virgo Snaps 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> |
| <div class="sect2"> |
| <h3 id="introduction-prereqs">1.2. Prerequisites</h3> |
| <div class="paragraph"> |
| <p>VS requires Virgo Server for Apache Tomcat and Java SE 6 |
| or later to be installed. Java is available from <a href="http://www.java.com/" class="bare">http://www.java.com/</a> |
| and elsewhere. Virgo Server for Apache Tomcat is available from |
| <a href="http://www.eclipse.org/virgo/download/">here</a>.</p> |
| </div> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="installation">2. Installing Virgo Snaps</h2> |
| <div class="sectionbody"> |
| <div class="sect2"> |
| <h3 id="installation-zip">2.1. Installing from the Zip Download</h3> |
| <div class="paragraph"> |
| <p>VS is distributed as a Zip file. This can be |
| downloaded from <a href="http://www.eclipse.org/virgo/download/">here</a>.</p> |
| </div> |
| <div class="paragraph"> |
| <p>Once the Zip file is unpacked you will find several things inside, |
| including a copy of this documentation in the <code>docs</code> folder. The layout |
| is shown below.</p> |
| </div> |
| <div class="imageblock"> |
| <div class="content"> |
| <img src="images/snapsZipFile.png" alt="snapsZipFile"> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Take the bundles and plan in the <code>dist</code> folder and place them in either |
| the <code>/repository/usr</code> or <code>/repository/ext</code> folder of your Virgo install. |
| Later you need the bundles in the <code>sample</code> folder. If you wish to view |
| the source for VS or its sample, then these are |
| in the <code>src</code> folder.</p> |
| </div> |
| <div class="paragraph"> |
| <p>In order to start the Snaps system as a part of your |
| Virgo Server for Apache Tomcat, the Snaps plan needs to be referenced from the |
| <code>initialArtifacts</code> property. This is located in the config file at |
| <code>${SERVER_HOME}/config/org.eclipse.virgo.kernel.userregion.properties</code>. |
| The property should be extended like this.</p> |
| </div> |
| <div class="literalblock"> |
| <div class="content"> |
| <pre>initialArtifacts=repository:plan/org.eclipse.virgo.kernel.userregion.springdm, |
| repository:plan/org.eclipse.virgo.web.tomcat, |
| repository:plan/org.eclipse.virgo.snaps</pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Now you are ready to check that Snaps is working.</p> |
| </div> |
| </div> |
| <div class="sect2"> |
| <h3 id="installation-post">2.2. Verifying it’s working</h3> |
| <div class="paragraph"> |
| <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> |
| </div> |
| <div class="literalblock"> |
| <div class="content"> |
| <pre><DE0004I> Starting plan 'org.eclipse.virgo.snaps' version '3.0.0'. |
| <DE0004I> Starting bundle 'org.eclipse.virgo.snaps.api' version '[version]'. |
| <DE0005I> Started bundle 'org.eclipse.virgo.snaps.api' version '[version]'. |
| <DE0004I> Starting bundle 'org.eclipse.virgo.snaps.core' version '[version]'. |
| <DE0005I> Started bundle 'org.eclipse.virgo.snaps.core' version '[version]'. |
| <DE0005I> Started plan 'org.eclipse.virgo.snaps' version '3.0.0'.</pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Open up the Virgo Admin Console by navigating to |
| <code><a href="http://localhost:8080/admin" class="bare">http://localhost:8080/admin</a></code> and then go to the artifacts tab to deploy |
| some new bundles. The first bundle to deploy is located at |
| <code>/sample/org.eclipse.virgo.snaps.sample.animal-[version].jar</code>, |
| select it in the browser and upload. In the terminal window you started |
| the Virgo Server for Apache Tomcat in you should see the usual messages about the |
| bundle starting and this message:</p> |
| </div> |
| <div class="literalblock"> |
| <div class="content"> |
| <pre><SN0000I> Host created for path '/animal-menu-bar'</pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <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><a href="http://localhost:8080/animal-menu-bar/" class="bare">http://localhost:8080/animal-menu-bar/</a></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> |
| </div> |
| <div class="paragraph"> |
| <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>/sample/org.eclipse.virgo.snaps.sample.dog-[version].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> |
| </div> |
| <div class="literalblock"> |
| <div class="content"> |
| <pre><SN0010I> Snap bound to path '/animal-menu-bar/dog'</pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <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> |
| </div> |
| <div class="imageblock"> |
| <div class="content"> |
| <img src="images/sampleDog.png" alt="sampleDog"> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <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> |
| </div> |
| <div class="sect1"> |
| <h2 id="using-snaps">3. Using Virgo Snaps in your application</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <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> |
| <div class="sect2"> |
| <h3 id="using-snaps-configuring-the-host">3.1. Configuring the Host</h3> |
| <div class="paragraph"> |
| <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 host’s <code>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>dispatcher</code> declarations in the |
| <code>filter-mapping</code>. Without these internal lookups, resources like JSPs |
| won’t get passed to the appropriate snap when needed.</p> |
| </div> |
| <div class="literalblock"> |
| <div class="content"> |
| <pre><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> |
| </div> |
| <div class="sect2"> |
| <h3 id="using-snaps-configuring-a-snap">3.2. Configuring a Snap</h3> |
| <div class="paragraph"> |
| <p>A snap is a normal WAB with the addition of two extra manifest headers. |
| The <code>Snap-Host</code> is used to resolve the WAB you want to act as a |
| host for this snap. The <code>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>Snap-ContextPath</code> header.</p> |
| </div> |
| <div class="literalblock"> |
| <div class="content"> |
| <pre>Snap-Host: org.eclipse.virgo.snaps.sample.animal;version="${version:[=.=.=, =.+1)}" |
| Snap-ContextPath: /dog</pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>For attaching a snap to multiple hosts, the <code>Snap-Host</code> allows the specification of |
| multiple host bundles. Given the example above, the Dog snap could be additionally |
| attached to the <code>Snap-Host</code> <code>org.eclipse.virgo.snaps.sample.zoo</code> as follows:</p> |
| </div> |
| <div class="literalblock"> |
| <div class="content"> |
| <pre>Snap-Host: org.eclipse.virgo.snaps.sample.animal,org.eclipse.virgo.snaps.sample.zoo |
| Snap-ContextPath: /dog</pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Even though a snap can be attached to multiple hosts, the <code>Snap-ContextPath</code> will |
| remain the same, which means that regardless of the <code>Snap-Host</code>, the snap |
| will be located under the same path. Multiple <code>Snap-Host</code> definitions might |
| be useful for snaps that hold resources required in multiple applications (for instance |
| third party libraries or functionality that can be reused across applications).</p> |
| </div> |
| </div> |
| <div class="sect2"> |
| <h3 id="using-snaps-taglibs">3.3. Using the Snaps taglibs</h3> |
| <div class="paragraph"> |
| <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><%@ 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>META-INF</code> |
| directory and have a name of <code>snap.properties</code>. The following code snippet |
| shows all of these in use to produce links to each of the installed snaps.</p> |
| </div> |
| <div class="literalblock"> |
| <div class="content"> |
| <pre><snaps:snaps var="snaps"> |
| <c:forEach var="snap" items="${snaps}"> |
| <a href="<c:url value="${snap.contextPath}${snap.properties['link.path']}"/>"> |
| ${snap.properties['link.text']}</a> |
| </c:forEach> |
| </snaps:snaps></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>The first line uses the Snaps tag library to place the array of snaps |
| into the <code>snaps</code> variable. Then a <code>forEach</code> loop goes through each snap. |
| The content of the <code>forEach</code> loop is the really interesting bit. The |
| first variable <code>${snap.contextPath}</code> returns the context path of the |
| snap. The two lookups are for properties |
| <code>${snap.properties['something']}</code>. They rely on the snap having the |
| properties file in place with <code>link.path</code> and <code>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> |
| <div class="sect2"> |
| <h3 id="using-snaps-host-prefix">3.4. Referencing Resources</h3> |
| <div class="paragraph"> |
| <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>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>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> |
| </div> |
| <div class="literalblock"> |
| <div class="content"> |
| <pre>request.getServletContext().getResource("host:/WEB-INF/sample.properties");</pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <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> |
| </div> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="sample-application">4. A Sample Application</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <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> |
| <div class="sect2"> |
| <h3 id="sample-application-structure">4.1. Structure of the sample application</h3> |
| <div class="paragraph"> |
| <p>The application is very simple, it consists of just a front end, |
| composed of four bundles, a host with three Snaps.</p> |
| </div> |
| <div class="imageblock"> |
| <div class="content"> |
| <img src="images/sampleApp.png" alt="sampleApp"> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>The host and three snaps show their <code>Snap-ContextPaths</code>. The Cat and Dog |
| snaps both contribute content while the final snap just contributes |
| styling information in the form of <code>css</code> files. The following sections |
| look at each of these in detail.</p> |
| </div> |
| </div> |
| <div class="sect2"> |
| <h3 id="sample-application-host">4.2. The Host bundle</h3> |
| <div class="paragraph"> |
| <p>This bundle is very simple with no Java code. It defines the Snaps |
| filter in its <code>web.xml</code> just as you have seen in the |
| <a href="#using-snaps-configuring-the-host">Using Snaps</a> section. The menu |
| bar uses the taglibs support to render links for each registered Snap.</p> |
| </div> |
| <div class="literalblock"> |
| <div class="content"> |
| <pre><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> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <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>/META-INF/snap.properties</code>.</p> |
| </div> |
| </div> |
| <div class="sect2"> |
| <h3 id="sample-application-new-content">4.3. Adding New Content</h3> |
| <div class="paragraph"> |
| <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> |
| </div> |
| <div class="imageblock"> |
| <div class="content"> |
| <img src="images/sampleCat.png" alt="sampleCat"> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <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>DispatcherServlet</code> defined in its <code>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> |
| </div> |
| <div class="literalblock"> |
| <div class="content"> |
| <pre>@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> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>There are two properties files called <code>sample.properties</code> located at the |
| same path within both the Cat snap and the host. Each contains a |
| property called <code>some.property</code> but with distinct value. Looking at the |
| code above you can see the <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> |
| <div class="sect2"> |
| <h3 id="sample-application-dynamic-styling">4.4. Re-styling</h3> |
| <div class="paragraph"> |
| <p>Finally the Blue styling snap shows how Snaps can be used in other ways. |
| Deploying this will cause all requests to <code>/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> |
| </div> |
| <div class="imageblock"> |
| <div class="content"> |
| <img src="images/sampleBlue.png" alt="sampleBlue"> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <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.</p> |
| </div> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="further-reading">5. Further Reading</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>The User and Programmer Guides provide a lot of information about using |
| and developing applications for the Virgo Server.</p> |
| </div> |
| <div class="paragraph"> |
| <p><a href="http://www.eclipse.org/virgo/documentation/">Virgo Documentation |
| page</a></p> |
| </div> |
| <div class="paragraph"> |
| <p><a href="../../virgo-programmer-guide/html/index.html">Virgo Server for Apache Tomcat |
| Programmer Guide</a></p> |
| </div> |
| <div class="paragraph"> |
| <p><a href="../../virgo-user-guide/html/index.html">Virgo Server for Apache Tomcat User |
| Guide</a></p> |
| </div> |
| <div class="paragraph"> |
| <p><a href="http://www.slideshare.net/cgfrost/eclipsecon2011-virgo-snaps">Slides from |
| a presentation at EclipseCon 2011 about Virgo Snaps.</a></p> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="known-issues">6. Known Issues</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>This section describes known issues that you might run into, along with |
| corresponding workarounds.</p> |
| </div> |
| <div class="sect2"> |
| <h3 id="known-issues-jetty-restriction">6.1. Virgo Jetty Server Restriction</h3> |
| <div class="paragraph"> |
| <p>Virgo Snaps is not supported on the Virgo Jetty Server, |
| please use with the Virgo Server for Apache Tomcat.</p> |
| </div> |
| </div> |
| </div> |
| </div> |
| </div> |
| </body> |
| </html> |
