打造一个基于OSGi的Web Application——设置初始化bundle的StartLevel

在前几天的文章中描述了如何在Web Application中启动OSGi，参见

打造一个基于OSGi的Web Application——在WebApplication中启动OSGi
后来发现其中在初始化时加载bundle的方式，还有一些美中不足。这种方式加载的bundle都具有相同的启动顺序，即bundle的初始化默认start level，在之前均没有做过特别的设置，所以默认值都是1，这样会导致所有的bundle的启动顺序无法控制，在某些希望特殊bundle优先加载的场合(如日志功能，需要最先加载)，我们希望能够在bundle初始化的时候就能指定特别的start level，这样所有的bundle就能按照我们预设的启动顺序来加载了。下面就是我优化过的初始化代码，能够解决启动顺序问题。

工作原理是这样的，首先，在原来存放初始化bundle的目录，也就是OSGi-Web工程的/WEB-INF/osgi/plugins目录下面再增加一个名为start的目录，在start目录下，再按照期望设置的start level来建立子目录，例如，期望设置start level为1的bundle，放到plugins/start/1目录下面；期望设置start level为2的bundle，放到plugins/start/2目录下面，以此类推。

代码方面，设置bundle的start level，需要使用StartLevel Service，可以通过下面代码获得：
1                 // StartLevel Service，用于设置bundle的startlevel
2                 ServiceReference slRef = bundleContext.getServiceReference(StartLevel.class.getName());
3                 StartLevel sl = slRef == null ? null : (StartLevel) bundleContext.getService(slRef);然后设置initial bundle start level：
1                 // 设置新bundle的初始startlevel为系统配置项：org.osgi.framework.startlevel.beginning的值
2                 String bsl = bundleContext.getProperty("org.osgi.framework.startlevel.beginning");
3                 if (bsl != null && isInteger(bsl)) sl.setInitialBundleStartLevel(Integer.parseInt(bsl));这样所有新安装的bundle的初始化start level都将被设置为和系统配置项：org.osgi.framework.startlevel.beginning相同的值，以确保所有默认安装的bundle都能启动。
修改osgi.properties中关于org.osgi.framework.startlevel.beginning的配置项，我改成了5：
1 #Specifies the beginning start level of the framework. See Start
2 #Level Service Specification on page 235 for more information.
3 #
4 org.osgi.framework.startlevel.beginning = 5

增加一个方法，用于安装一个目录下所有的直属bundle，并且设置start level：
1     private static void installBundles(BundleContext bundleContext, File bundleRoot, StartLevel sl, int bsl) {
2         File bundleFiles[] = bundleRoot.listFiles(new FilenameFilter() {
3             public boolean accept(File dir, String name) {
4                 return name.endsWith(".jar");
5             }
6         });
7
8         if (bundleFiles != null && bundleFiles.length > 0) {
9             for (File bundleFile : bundleFiles) {
10                 try {
11                     Bundle bundle = bundleContext.installBundle(bundleFile.toURL().toExternalForm());
12                     if (sl != null && bsl > 0) sl.setBundleStartLevel(bundle, bsl);
13                     if (logger.isInfoEnabled()) logger.info("Install bundle success: " + bundleFile.getName());
14                 } catch (Throwable e) {
15                     if (logger.isWarnEnabled()) logger.warn("Install bundle error: " + bundleFile, e);
16                 }
17             }
18         }
19     }
最后，遍历start目录下的子目录来安装所有的bundle：
1                 // 安装bundle并设置相应的start level
2                 File slRoot = new File(bundleRoot, "start");
3                 if (slRoot.isDirectory()) {
4                     File slDirs[] = slRoot.listFiles(new FileFilter() {
5                         public boolean accept(File file) {
6                             return file.isDirectory() && isInteger(file.getName());
7                         }
8                     });
9
10                     for (File slDir : slDirs) {
11                         installBundles(bundleContext, slDir, sl, Integer.parseInt(slDir.getName()));
12                     }
13                 }
14
15                 // 安装直属目录下面的bundle
16                 installBundles(bundleContext, bundleRoot, sl, 0);
1     private static boolean isInteger(String value) {
2         try {
3             Integer.parseInt(value);
4             return true;
5         } catch (NumberFormatException e) {
6             return false;
7         }
8     }
最后，由于Declarative Services的存在，稍微调整了一下启动策略，所有包含Service-Component的header定义的bundle，也调用start方法来启动：
1                 for (Bundle bundle : bundleContext.getBundles()) {
2                     if (bundle.getState() == Bundle.INSTALLED || bundle.getState() == Bundle.RESOLVED) {
3                         if (bundle.getHeaders().get(Constants.BUNDLE_ACTIVATOR) != null || bundle.getHeaders().get("Service-Component") != null) {
4                             try {
5                                 bundle.start(Bundle.START_ACTIVATION_POLICY);
6                                 if (logger.isInfoEnabled()) logger.info("Start bundle: " + bundle);
7                             } catch (Throwable e) {
8                                 if (logger.isWarnEnabled()) logger.warn("Start bundle error: " + bundle, e);
9                             }
10                         }
11                     }
12                 }
clean Server然后启动Server，我们可以看到初始化后的bundle已经被赋予了指定Start Level。


附上initFramework方法的完整代码，更多的代码请参加以前的帖子：
1     // 初始化Framework环境
2     private static void initFramework(Framework framework, ServletContextEvent event) throws IOException {
3         BundleContext bundleContext = framework.getBundleContext();
4         ServletContext servletContext = event.getServletContext();
5
6         // 将ServletContext注册为服务
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             // 安装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                 // StartLevel Service，用于设置bundle的startlevel
23                 ServiceReference slRef = bundleContext.getServiceReference(StartLevel.class.getName());
24                 StartLevel sl = slRef == null ? null : (StartLevel) bundleContext.getService(slRef);
25                 // 设置新bundle的初始startlevel为系统配置项：org.osgi.framework.startlevel.beginning的值
26                 String bsl = bundleContext.getProperty("org.osgi.framework.startlevel.beginning");
27                 if (bsl != null && isInteger(bsl)) sl.setInitialBundleStartLevel(Integer.parseInt(bsl));
28
29                 // 安装bundle并设置相应的start level
30                 File slRoot = new File(bundleRoot, "start");
31                 if (slRoot.isDirectory()) {
32                     File slDirs[] = slRoot.listFiles(new FileFilter() {
33                         public boolean accept(File file) {
34                             return file.isDirectory() && isInteger(file.getName());
35                         }
36                     });
37
38                     for (File slDir : slDirs) {
39                         installBundles(bundleContext, slDir, sl, Integer.parseInt(slDir.getName()));
40                     }
41                 }
42
43                 // 安装直属目录下面的bundle
44                 installBundles(bundleContext, bundleRoot, sl, 0);
45
46                 for (Bundle bundle : bundleContext.getBundles()) {
47                     if (bundle.getState() == Bundle.INSTALLED || bundle.getState() == Bundle.RESOLVED) {
48                         if (bundle.getHeaders().get(Constants.BUNDLE_ACTIVATOR) != null || bundle.getHeaders().get("Service-Component") != null) {
49                             try {
50                                 bundle.start(Bundle.START_ACTIVATION_POLICY);
51                                 if (logger.isInfoEnabled()) logger.info("Start bundle: " + bundle);
52                             } catch (Throwable e) {
53                                 if (logger.isWarnEnabled()) logger.warn("Start bundle error: " + bundle, e);
54                             }
55                         }
56                     }
57                 }
58
59                 if (slRef != null) bundleContext.ungetService(slRef);
60             }
61
62             new FileWriter(file).close();
63             if (logger.isInfoEnabled()) logger.info("Framework inited.");
64         }
65     }