eclipse bundle类加载器

     Eclipse各bundle使用各自的class loader，若需要引用其他bundle类来动态创建实例，则需要使用类所在的bundle的class loader。

    下面实例演示如何使用其它bundle类。

    当前plugin为rpc服务器，需要使用其它任意使用了rpc的bundle类。实现方式：在本plugin定义扩展点，定义出class loader接口--BizClassLoader，其它bundle扩展这个扩展点，并实现BizClassLoader

 

1) 定义扩展点：

1)

 

BizClassLoader接口

 

 public interface RPCClassLoader { public Class<?> loadClass(String className) throws ClassNotFoundException; } public interface BizClassLoader extends RPCClassLoader{ }

 

2) Bundle类加载器，使用所有扩展的BizClassLoader，并监听扩展bundle的新增删除，以同步bundle类加载器。尝试多个ClassLoader加载类，必然有性能问题，因此需使用cache，这样只影响第一次加载。

/** * 资源类加载器：通过扩展点，加载扩展bundle中的类。 //TODO 线程安全(一般很少add/remove Extension) * * @author js * */ public class BundleClassLoader implements RPCClassLoader { private final static Log log = LogFactory.getLog(BundleClassLoader.class); public final static String POINT_LOADER = "BizClassLoader"; public final static String POINT_LOADER_EXECUTEABLE = "loader"; // 插件.扩展点ID private String extensionPoint = Activator.PLUGIN_ID + "." + POINT_LOADER; private List<ExtensionClassLoader> loaderList = new ArrayList<ExtensionClassLoader>(); private Map<String, Class<?>> clazzMap = new HashMap<String, Class<?>>(); private class ExtensionClassLoader { IExtension e; BizClassLoader loader; Set<String> classNameSet = new HashSet<String>(); ExtensionClassLoader(IExtension e) { this.e = e; IConfigurationElement[] elements = e.getConfigurationElements(); try { // 用IConfigurationElement #createExecutableExtension创建新对象 loader = (BizClassLoader) elements[0] .createExecutableExtension(POINT_LOADER_EXECUTEABLE); } catch (CoreException e1) { log.error(e1.getMessage(), e1); } } } public BundleClassLoader(BundleContext context) { // 注册监听器 IExtensionRegistry registry = Platform.getExtensionRegistry(); registry.addRegistryChangeListener(new IRegistryChangeListener() { @Override public void registryChanged(IRegistryChangeEvent e) { IExtensionDelta[] ds = e.getExtensionDeltas( Activator.PLUGIN_ID, POINT_LOADER); for (int i = 0, n = ds.length; i < n; i++) { IExtensionDelta d = ds[i]; if (d.getKind() == IExtensionDelta.ADDED) { // 新增 onAddExtension(d.getExtension()); } else if (d.getKind() == IExtensionDelta.REMOVED) { // 删除 onRemoveExtension(d.getExtension()); } } } }, Activator.PLUGIN_ID); IExtension[] es = registry.getExtensionPoint(extensionPoint) .getExtensions(); for (int i = 0, n = es.length; i < n; i++) { onAddExtension(es[i]); } } private void onAddExtension(IExtension e) { log.info("Add extension " + e); loaderList.add(new ExtensionClassLoader(e)); } private void onRemoveExtension(IExtension e) { log.info("Remove extension " + e); for (int i = 0, n = loaderList.size(); i < n; i++) { ExtensionClassLoader ec = loaderList.get(i); if (ec.e == e) { loaderList.remove(i); clazzMap.keySet().removeAll(ec.classNameSet); break; } } } @Override public Class<?> loadClass(String className) throws ClassNotFoundException { Class<?> clazz = null; if (clazzMap.containsKey(className)) { clazz = clazzMap.get(className); } else { try { // 使用本地 clazz = Class.forName(className); } catch (ClassNotFoundException e) { } if (clazz == null) { // 使用扩展 for (int i = 0, n = loaderList.size(); i < n; i++) { ExtensionClassLoader ec = loaderList.get(i); try { clazz = ec.loader.loadClass(className); ec.classNameSet.add(className); break; } catch (ClassNotFoundException e) { } } } clazzMap.put(className, clazz); } if (clazz == null) { log.error("Class not found:" + className + "."); throw new ClassNotFoundException(className); } return clazz; } }

 

3) 其他插件实现扩展

 

 

注意类加载器必须实现loadClass方法，不能使用因为父类实现了，便省了。因为父类不一定在本bundle，因此classLoader不同。

public class BizClassLoader implements com.js.km.rpc.engine.extension.BizClassLoader { public BizClassLoader() { } @Override public Class<?> loadClass(String className) throws ClassNotFoundException { return Class.forName(className); } }

 

4) 上面已实现定义、扩展，接下来就可使用boundle加载器了，本例使用读对象流：

用bundle类加载器加载流使用的类。

public class ObjectInputStreamWithLoader extends ObjectInputStream { private RPCClassLoader myLoader = null; public ObjectInputStreamWithLoader(InputStream inputstream, RPCClassLoader myLoader) throws StreamCorruptedException, IOException, SecurityException { super(inputstream); this.myLoader = myLoader; } protected Class<?> resolveClass(ObjectStreamClass desc) throws IOException, ClassNotFoundException { return myLoader.loadClass(desc.getName()); } }