| <html><head> |
| <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> |
| <title>3. GreenPages Highlights</title><link rel="stylesheet" href="css/stylesheet.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.74.0"><link rel="home" href="index.html" title="A Guide to the GreenPages Sample"><link rel="up" href="index.html" title="A Guide to the GreenPages Sample"><link rel="prev" href="ch02s05.html" title="2.5 Running GreenPages from Eclipse"><link rel="next" href="ch03s02.html" title="3.2 Middle Tier Highlights"><!--Begin Google Analytics code--><script type="text/javascript"> |
| var gaJsHost = (("https:" == document.location.protocol) ? "https://ssl." : "http://www."); |
| document.write(unescape("%3Cscript src='" + gaJsHost + "google-analytics.com/ga.js' type='text/javascript'%3E%3C/script%3E")); |
| </script><script type="text/javascript"> |
| var pageTracker = _gat._getTracker("UA-2728886-3"); |
| pageTracker._setDomainName("none"); |
| pageTracker._setAllowLinker(true); |
| pageTracker._trackPageview(); |
| </script><!--End Google Analytics code--></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">3. GreenPages Highlights</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch02s05.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="ch03s02.html">Next</a></td></tr></table><hr></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="highlights"></a>3. GreenPages Highlights</h2></div></div></div><p> |
| This chapter picks out some notable features of the GreenPages sample code from the <code class="literal">greenpages.*</code> folders. |
| </p><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="highlights.wab"></a>3.1 Web Application Bundle Highlights</h2></div></div></div><p> |
| The GreenPages Web Application Bundle (WAB) is built using Spring MVC configured with Spring annotations and component |
| scanning. The Bundlor tool is used to generate the bundle manifest of the WAB and a service is injected into the code |
| using Spring DM in combination with Spring autowiring. |
| </p><p> |
| For more information on Spring, Spring MVC, Bundlor and Spring DM, please see <a class="link" href="apa.html#further.resources.projects" title="A.1 Projects">Projects</a>.. |
| </p><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="d0e791"></a>web.xml</h3></div></div></div><p> |
| The web deployment descriptor file <code class="literal">web.xml</code> is in the <code class="literal">src/main/webapp/WEB_INF</code> folder of the |
| <code class="literal">greenpages.web</code> project. |
| It defines a servlet, a servlet context parameter, and a servlet context listener. |
| </p><p> |
| Spring's dispatcher servlet is used to dispatch web requests to handlers. |
| </p><pre class="programlisting"> <servlet> |
| <servlet-name>greenpages</servlet-name> |
| <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> |
| </servlet> |
| </pre><p> |
| </p><p> |
| The <code class="literal">contextClass</code> servlet parameter declares the implementation of <code class="interfacename">WebApplicationContext</code> |
| that Spring instantiates. |
| The application context acts as a root application context and each servlet in the web application, which in the case of GreenPages is |
| just the dispatcher servlet, has its own application context which is a child of the root application context. |
| <code class="classname">ServerOsgiBundleXmlWebApplicationContext</code> is provided by Virgo and will hold beans created by Spring DM, which |
| are then available in child application contexts. |
| </p><pre class="programlisting"> <context-param> |
| <param-name>contextClass</param-name> |
| <param-value>org.eclipse.virgo.web.dm.ServerOsgiBundleXmlWebApplicationContext</param-value> |
| </context-param> |
| |
| </pre><p> |
| </p><p> |
| A servlet context listener is defined which will start up the root application context for the web application when the servlet context |
| is initialised. |
| </p><pre class="programlisting"> <listener> |
| <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class> |
| </listener> |
| |
| </pre><p> |
| </p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="d0e829"></a>Controller Class</h3></div></div></div><p> |
| In the <code class="literal">src/main/java</code> source folder of the <code class="literal">greenpages.web</code> project |
| the package <code class="classname">greenpages.web</code> |
| contains the controller class <code class="classname">GreenPagesController</code>. |
| </p><p> |
| Spring annotations are used to add web behaviour to the class. |
| The <code class="classname">@Controller</code> annotation tells Spring that the class serves the role of a controller and that the |
| class should be scanned for <span class="emphasis"><em>request mappings</em></span>. |
| Request mappings are defined using the <code class="classname">@RequestMapping</code> annotation. |
| For instance, the URL <code class="literal">/home.htm</code> is mapped to the handler method <code class="literal">home</code>. |
| </p><pre class="programlisting">@Controller |
| <span class="hl-keyword">public</span> <span class="hl-keyword">class</span> GreenPagesController { |
| … |
| @RequestMapping(<span class="hl-string">"/home.htm"</span>) |
| <span class="hl-keyword">public</span> <span class="hl-keyword">void</span> home() { |
| } |
| … |
| </pre><p> |
| Note that request mappings can also be specified at the class level. |
| </p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="d0e866"></a>Component Scanning</h3></div></div></div><p> |
| Spring will detect the <code class="classname">@Controller</code> annotation and create a bean of type controller, |
| <span class="emphasis"><em>provided that</em></span> it scans the classpath for these. |
| Spring’s component scanning is enabled by the presence of a <code class="literal">context</code> tag |
| in one of the Spring bean definition files. |
| </p><p> |
| The <code class="filename">WEB-INF/greenpages-servlet.xml</code> file in the |
| <code class="literal">src/main/webapp</code> folder contains the following lines: |
| </p><pre class="programlisting"><<span class="hl-comment">!-- enable classpath scanning --</span>> |
| <<span class="hl-tag">context:component-scan</span> <span class="hl-attribute">base-package</span>=<span class="hl-value">"greenpages.web"</span> /> |
| </pre><p> |
| Notice the convention embodied in the filename <code class="filename">WEB-INF/greenpages-servlet.xml</code>. |
| During dispatcher servlet initialisation, Spring looks for a file named <code class="literal">[servlet-name]-servlet.xml</code> |
| in the <code class="literal">WEB-INF</code> directory of the web application and creates the beans defined there. |
| </p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="d0e900"></a>Bundle Manifest</h3></div></div></div><p> |
| The Virgo Tomcat Server has special support for WABs. |
| To take advantage of this support, the <code class="literal">greenpages.web</code> bundle must be declared to be a WAB and a |
| context path must be defined. |
| </p><p> |
| The Bundlor template (the file <code class="filename">template.mf</code> at the top level under the <code class="literal">greenpages.web</code> project) |
| is input to the Bundlor tool which generates the manifest of the bundle. |
| </p><p> |
| The Bundlor template defines the context path as follows (and this is what declares the bundle to be a WAB): |
| </p><pre class="programlisting">Web-ContextPath: greenpages |
| </pre><p> |
| </p><p> |
| The Bundlor template also ensures Spring packages and greenpages packages from other bundles are imported with suitable version ranges: |
| </p><pre class="programlisting">Import-Template: |
| org.springframework.*;version="[3.0, 3.1)", |
| greenpages.*;version="[2.3, 2.4)" |
| </pre><p> |
| </p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="d0e926"></a>Service Injection</h3></div></div></div><p> |
| The file <code class="filename">webapp/WEB-INF/applicationContext.xml</code> declares a reference to a |
| <code class="interfacename">greenpages.Directory</code> service in the service registry using Spring DM as follows: |
| </p><pre class="programlisting"><<span class="hl-tag">osgi:reference</span> <span class="hl-attribute">id</span>=<span class="hl-value">"directory"</span> <span class="hl-attribute">interface</span>=<span class="hl-value">"greenpages.Directory"</span>/> |
| </pre><p> |
| The resultant bean resides in the root web application context. |
| </p><p> |
| The <code class="classname">GreenPagesController</code> class uses Spring autowiring to inject the service: |
| </p><pre class="programlisting">@Autowired |
| <span class="hl-keyword">private</span> Directory directory; |
| </pre><p> |
| The controller's bean resides in the web application context associated with the Spring dispatcher servlet and so has |
| access to the directory service bean in the root web application context. |
| </p></div></div></div><!--Begin LoopFuse code--><script src="http://loopfuse.net/webrecorder/js/listen.js" type="text/javascript"></script><script type="text/javascript"> |
| _lf_cid = "LF_48be82fa"; |
| _lf_remora(); |
| </script><!--End LoopFuse code--><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ch02s05.html">Prev</a> </td><td width="20%" align="center"> </td><td width="40%" align="right"> <a accesskey="n" href="ch03s02.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">2.5 Running GreenPages from Eclipse </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 3.2 Middle Tier Highlights</td></tr></table></div></body></html> |
