打造一個基於OSGi的Web Application——在WebApplication中啓動OSGi

本章將創建一個Web Application項目，並描述如何在此應用中啓動OSGi。

首先，在Eclipse中創建一個Dynamic Web Project，名字爲OSGi-Web，Context root爲osgi。

這個項目只作爲部署Web Application使用，相關java代碼放在另外一個Java Project中，因此我們再創建一個新的Java Project，名字爲OSGi-Web-Launcher。然後在OSGi-Web項目的Java EE Module Dependencies中設置OSGi-Web-Launcher爲關聯，這樣在部署的時候，OSGi-Web-Launcher項目中的java代碼將爲打包爲jar存放到Web的WEB-INF/lib目錄之中。

爲了啓動OSGi，我們在web中增加一個ServletContextListener監聽器實現，並且通過這個監聽器來控制OSGi容器的啓動和終止。

在OSGi-Web-Launcher項目中增加一個java類，類名爲FrameworkConfigListener，實現接口ServletContextListener，package爲org.dbstar.osgi.web.launcher。在contextInitialized方法中，增加啓動OSGi的代碼，在contextDestroyed方法中，增加停止OSGi的代碼，這樣我們就可以使OSGi容器的生命週期與ServletContext的生命週期保持一致了。

啓動OSGi容器：
感謝OSGi規範4.2給了我們一個簡單統一的啓動OSGi容器的方式，所有實現OSGi4.2規範的容器實力都應該實現這種啓動方式，那就是通過org.osgi.framework.launch.FrameworkFactory，同時，還必須在其實現jar中放置一個文件：META-INF/services/org.osgi.framework.launch.FrameworkFactory，這個文件中設置了實際的FrameworkFactory實現類的類名。在equinox-SDK-3.6M5的org.eclipse.osgi_3.6.0.v20100128-1430.jar中，這個文件的內容是：org.eclipse.osgi.launch.EquinoxFactory。

我們先寫一個工具類來載入這個配置文件中的內容：

<!--<br /> <br /> Code highlighting produced by Actipro CodeHighlighter (freeware)<br /> http://www.CodeHighlighter.com/<br /> <br /> --> 1  package  org.dbstar.osgi.web.launcher;
 2  
 3  import  java.io.BufferedReader;
 4  import  java.io.IOException;
 5  import  java.io.InputStream;
 6  import  java.io.InputStreamReader;
 7  
 8  public   abstract   class  ServiceLoader {
 9       public   final   static   < E >  Class < E >  load(Class < E >  clazz)  throws  IOException, ClassNotFoundException {
10           return  load(clazz, Thread.currentThread().getContextClassLoader());
11      }
12  
13      @SuppressWarnings( " unchecked " )
14       public   final   static   < E >  Class < E >  load(Class < E >  clazz, ClassLoader classLoader)  throws  IOException,
15              ClassNotFoundException {
16          String resource  =   " META-INF/services/ "   +  clazz.getName();
17          InputStream in  =  classLoader.getResourceAsStream(resource);
18           if  (in  ==   null )  return   null ;
19  
20           try  {
21              BufferedReader reader  =   new  BufferedReader( new  InputStreamReader(in));
22              String serviceClassName  =  reader.readLine();
23               return  (Class < E > ) classLoader.loadClass(serviceClassName);
24          }  finally  {
25              in.close();
26          }
27      }
28  }

然後獲取到FrameworkFactory的實例類：

<!--<br /> <br /> Code highlighting produced by Actipro CodeHighlighter (freeware)<br /> http://www.CodeHighlighter.com/<br /> <br /> -->1               try  {
2                  frameworkFactoryClass  =  ServiceLoader.load(FrameworkFactory. class );
3              }  catch  (Exception e) {
4                   throw   new  IllegalArgumentException( " FrameworkFactory service load error. " , e);
5              }
6               if  (frameworkFactoryClass  ==   null ) {
7                   throw   new  IllegalArgumentException( " FrameworkFactory service not found. " );
8              }

實例化FrameworkFactory：

<!--<br /> <br /> Code highlighting produced by Actipro CodeHighlighter (freeware)<br /> http://www.CodeHighlighter.com/<br /> <br /> -->1              FrameworkFactory frameworkFactory;
2               try  {
3                  frameworkFactory  =  frameworkFactoryClass.newInstance();
4              }  catch  (Exception e) {
5                   throw   new  IllegalArgumentException( " FrameworkFactory instantiation error. " , e);
6              }

獲取Framework的啓動配置：

<!--<br /> <br /> Code highlighting produced by Actipro CodeHighlighter (freeware)<br /> http://www.CodeHighlighter.com/<br /> <br /> --> 1              Map < Object, Object >  configuration;
 2               try  {
 3                   //  載入Framework啓動配置
 4                  configuration  =  loadFrameworkConfig(event.getServletContext());
 5                   if  (logger.isInfoEnabled()) {
 6                      logger.info( " Load Framework configuration: [ " );
 7                       for  (Object key : configuration.keySet()) {
 8                          logger.info( " \t "   +  key  +   "  =  "   +  configuration.get(key));
 9                      }
10                      logger.info( " ] " );
11                  }
12              }  catch  (Exception e) {
13                   throw   new  IllegalArgumentException( " Load Framework configuration error. " , e);
14              }

啓動配置讀取外部配置文件，可以在此配置文件中增加OSGi容器實現類相關的配置項，例如Equinox的osgi.console：

<!--<br /> <br /> Code highlighting produced by Actipro CodeHighlighter (freeware)<br /> http://www.CodeHighlighter.com/<br /> <br /> --> 1       //  載入Framework啓動配置
 2       private   static  Map < Object, Object >  loadFrameworkConfig(ServletContext context)  throws  MalformedURLException {
 3          String configLocation  =  context.getInitParameter(CONTEXT_PARAM_OSGI_CONFIG_LOCATION);
 4           if  (configLocation  ==   null ) configLocation  =  DEFAULT_OSGI_CONFIG_LOCATION;
 5           else   if  ( ! configLocation.startsWith( " / " )) configLocation  =   " / " .concat(configLocation);
 6  
 7          Properties config  =   new  Properties();
 8           try  {
 9               //  載入配置項
10              config.load(context.getResourceAsStream(configLocation));
11               if  (logger.isInfoEnabled()) logger.info( " Load Framework configuration from:  "   +  configLocation);
12          }  catch  (IOException e) {
13               if  (logger.isWarnEnabled()) logger.warn( " Load Framework configuration error from:  "   +  configLocation, e);
14          }
15  
16          String storageDirectory  =  config.getProperty(PROPERTY_FRAMEWORK_STORAGE, DEFAULT_OSGI_STORAGE_DIRECTORY);
17           //  檢查storageDirectory合法性
18           if  (storageDirectory.startsWith(WEB_ROOT)) {
19               //  如果以WEB_ROOT常量字符串開頭，那麼相對於WEB_ROOT來定位
20              storageDirectory  =  storageDirectory.substring(WEB_ROOT.length());
21              storageDirectory  =  context.getRealPath(storageDirectory);
22          }  else  {
23               //  如果是相對路徑，那麼相對於WEB_ROOT來定位
24               if  ( ! new  File(storageDirectory).isAbsolute()) {
25                  storageDirectory  =  context.getRealPath(storageDirectory);
26              }
27          }
28          storageDirectory  =   new  File(storageDirectory).toURL().toExternalForm();
29          config.setProperty(PROPERTY_FRAMEWORK_STORAGE, storageDirectory);
30           if  (logger.isInfoEnabled()) logger.info( " Use Framework Storage:  "   +  storageDirectory);
31  
32           return  config;
33      }

然後，就可以獲取framework實例了，通過framework來初始化，啓動和停止OSGi容器：

<!--<br /> <br /> Code highlighting produced by Actipro CodeHighlighter (freeware)<br /> http://www.CodeHighlighter.com/<br /> <br /> --> 1               try  {
 2                  framework  =  frameworkFactory.newFramework(configuration);
 3                  framework.init();
 4  
 5                   //  初始化Framework環境
 6                  initFramework(framework, event);
 7  
 8                   //  啓動Framework
 9                  framework.start();
10  
11                  succeed  =   true ;
12              }  catch  (BundleException e) {
13                   throw   new  OSGiStartException( " Start OSGi Framework error! " , e);
14              }  catch  (IOException e) {
15                   throw   new  OSGiStartException( " Init OSGi Framework error " , e);
16              }

在initFramework方法中，主要做兩件事情，一是將當前的ServletContext作爲一個service註冊到OSGi容器中去：

<!--<br /> <br /> Code highlighting produced by Actipro CodeHighlighter (freeware)<br /> http://www.CodeHighlighter.com/<br /> <br /> -->1       private   static   void  registerContext(BundleContext bundleContext, ServletContext servletContext) {
2          Properties properties  =   new  Properties();
3          properties.setProperty( " ServerInfo " , servletContext.getServerInfo());
4          properties.setProperty( " ServletContextName " , servletContext.getServletContextName());
5          properties.setProperty( " MajorVersion " , String.valueOf(servletContext.getMajorVersion()));
6          properties.setProperty( " MinorVersion " , String.valueOf(servletContext.getMinorVersion()));
7          bundleContext.registerService(ServletContext. class .getName(), servletContext, properties);
8      }

第二件事就是：在第一次初始化容器時，加載並啓動指定目錄中的bundle：

<!--<br /> <br /> Code highlighting produced by Actipro CodeHighlighter (freeware)<br /> http://www.CodeHighlighter.com/<br /> <br /> --> 1       //  初始化Framework環境
 2       private   static   void  initFramework(Framework framework, ServletContextEvent event)  throws  IOException {
 3          BundleContext bundleContext  =  framework.getBundleContext();
 4          ServletContext servletContext  =  event.getServletContext();
 5  
 6           //  將ServletContext註冊爲服務
 7          registerContext(bundleContext, servletContext);
 8  
 9          File file  =  bundleContext.getDataFile( " .init " );
10           if  ( ! file.isFile()) {  //  第一次初始化
11               if  (logger.isInfoEnabled()) logger.info( " Init Framework " );
12  
13              String pluginLocation  =  servletContext.getInitParameter(CONTEXT_PARAM_OSGI_PLUGINS_LOCATION);
14               if  (pluginLocation  ==   null ) pluginLocation  =  DEFAULT_OSGI_PLUGINS_LOCATION;
15               else   if  ( ! pluginLocation.startsWith( " / " )) pluginLocation  =   " / " .concat(pluginLocation);
16  
17               //  安裝bundle
18              File bundleRoot  =   new  File(servletContext.getRealPath(pluginLocation));
19               if  (bundleRoot.isDirectory()) {
20                   if  (logger.isInfoEnabled()) logger.info( " Load Framework bundles from:  "   +  pluginLocation);
21  
22                  File bundleFiles[]  =  bundleRoot.listFiles( new  FilenameFilter() {
23                       public   boolean  accept(File dir, String name) {
24                           return  name.endsWith( " .jar " );
25                      }
26                  });
27  
28                   if  (bundleFiles  !=   null   &&  bundleFiles.length  >   0 ) {
29                       for  (File bundleFile : bundleFiles) {
30                           try  {
31                              bundleContext.installBundle(bundleFile.toURL().toExternalForm());
32                               if  (logger.isInfoEnabled()) logger.info( " Install bundle success:  "   +  bundleFile.getName());
33                          }  catch  (Throwable e) {
34                               if  (logger.isWarnEnabled()) logger.warn( " Install bundle error:  "   +  bundleFile, e);
35                          }
36                      }
37                  }
38  
39                   for  (Bundle bundle : bundleContext.getBundles()) {
40                       if  (bundle.getState()  ==  Bundle.INSTALLED  ||  bundle.getState()  ==  Bundle.RESOLVED) {
41                           if  (bundle.getHeaders().get(Constants.BUNDLE_ACTIVATOR)  !=   null ) {
42                               try  {
43                                  bundle.start(Bundle.START_ACTIVATION_POLICY);
44                                   if  (logger.isInfoEnabled()) logger.info( " Start bundle:  "   +  bundle);
45                              }  catch  (Throwable e) {
46                                   if  (logger.isWarnEnabled()) logger.warn( " Start bundle error:  "   +  bundle, e);
47                              }
48                          }
49                      }
50                  }
51              }
52  
53               new  FileWriter(file).close();
54               if  (logger.isInfoEnabled()) logger.info( " Framework inited. " );
55          }
56      }

以上就是啓動OSGi容器的過程，相比較而言，停止容器就簡單多了：

<!--<br /> <br /> Code highlighting produced by Actipro CodeHighlighter (freeware)<br /> http://www.CodeHighlighter.com/<br /> <br /> --> 1       public   void  contextDestroyed(ServletContextEvent event) {
 2           if  (framework  !=   null ) {
 3               if  (logger.isInfoEnabled()) logger.info( " Stopping OSGi Framework " );
 4  
 5               boolean  succeed  =   false ;
 6               try  {
 7                   if  (framework.getState()  ==  Framework.ACTIVE) framework.stop();
 8                  framework.waitForStop( 0 );
 9                  framework  =   null ;
10  
11                  succeed  =   true ;
12              }  catch  (BundleException e) {
13                   throw   new  OSGiStopException( " Stop OSGi Framework error! " , e);
14              }  catch  (InterruptedException e) {
15                   throw   new  OSGiStopException( " Stop OSGi Framework error! " , e);
16              }  finally  {
17                   if  (logger.isInfoEnabled()) {
18                       if  (succeed) logger.info( " OSGi Framework Stopped! " );
19                       else  logger.info( " OSGi Framework not stop! " );
20                  }
21              }
22          }
23      }

最後，還有一件事情，就是將FrameworkConfigListener配置到web.xml中：

<!--<br /> <br /> Code highlighting produced by Actipro CodeHighlighter (freeware)<br /> http://www.CodeHighlighter.com/<br /> <br /> -->1       <!--  Init OSGi framework  -->
2       < listener >
3           < listener-class > org.dbstar.osgi.web.launcher.FrameworkConfigListener </ listener-class >
4       </ listener >

讓我們來測試一下吧，在Eclipse中新建一個Server：



另外，在OSGi-Web-Launcher項目的classpath中增加org.eclipse.osgi_3.6.0.v20100128-1430.jar，並且在Java EE Module Dependencies中勾選這個jar，這樣可以保證這個jar最終部署到Web Application的WEB-INF/lib目錄下去。同樣，還需要增加commons-logging.jar。

然後就可以啓動這個Server查看效果了。

附上本文中提到的源代碼 。