Struts2 中出现的Jdk动态代理实例和方法

package com.opensymphony.xwork2.inject;import java.lang.reflect.InvocationHandler;import java.lang.reflect.Method;import java.lang.reflect.InvocationTargetException;import java.lang.reflect.Proxy;import java.util.List;import java.util.ArrayList;/** * Context of a dependency construction. Used to manage circular references. * * @author crazybob@google.com (Bob Lee) */class ConstructionContext<T> {  T currentReference;  boolean constructing;  List<DelegatingInvocationHandler<T>> invocationHandlers;  T getCurrentReference() {    return currentReference;  }  void removeCurrentReference() {    this.currentReference = null;  }  void setCurrentReference(T currentReference) {    this.currentReference = currentReference;  }  boolean isConstructing() {    return constructing;  }  void startConstruction() {    this.constructing = true;  }  void finishConstruction() {    this.constructing = false;    invocationHandlers = null;  }    //此处应该是该方法的核心//  Object createProxy(Class<? super T> expectedType) {    // TODO: if I create a proxy which implements all the interfaces of    // the implementation type, I'll be able to get away with one proxy    // instance (as opposed to one per caller).    if (!expectedType.isInterface()) {      throw new DependencyException(          expectedType.getName() + " is not an interface.");    }    if (invocationHandlers == null) {      invocationHandlers = new ArrayList<DelegatingInvocationHandler<T>>();    }    DelegatingInvocationHandler<T> invocationHandler =        new DelegatingInvocationHandler<T>();    invocationHandlers.add(invocationHandler);        return Proxy.newProxyInstance(      expectedType.getClassLoader(), // 加载接口的类加载器      new Class[] { expectedType }, // 接口集合      invocationHandler  // handler处理类    );  } // 注意此处调用方法 中的参数 和值  认真看看希望能看出端倪来。此处很妙  void setProxyDelegates(T delegate) {    if (invocationHandlers != null) {      for (DelegatingInvocationHandler<T> invocationHandler : invocationHandlers) {        invocationHandler.setDelegate(delegate);      }    }  }// 内部静态类  static class DelegatingInvocationHandler<T> implements InvocationHandler {    T delegate;    public Object invoke(Object proxy, Method method, Object[] args)        throws Throwable {      if (delegate == null) {        throw new IllegalStateException(            "Not finished constructing. Please don't call methods on this"                + " object until the caller's construction is complete.");      }      try {     // method.invoke 中的参数 代理类  和要传入的参数        return method.invoke(delegate, args);                 //method方法应该是delegate接口中的      } catch (IllegalAccessException e) {        throw new RuntimeException(e);      } catch (IllegalArgumentException e) {        throw new RuntimeException(e);      } catch (InvocationTargetException e) {        throw e.getTargetException();      }    }        // 此处为何留一个接口方法呢？    void setDelegate(T delegate) {      this.delegate = delegate;    }  }}

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