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Java example source code file (DelegatingInvocationHandler.java)

This example Java source code file (DelegatingInvocationHandler.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

delegatinginvocationhandler, illegalaccessexception, illegalargumentexception, invocationhandler, invocationtargetexception, method, object, please, reflection, runtimeexception, the, this, throwable

The DelegatingInvocationHandler.java Java example source code

/**
 * Copyright (C) 2009 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.inject.internal;


import com.google.common.base.Preconditions;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

class DelegatingInvocationHandler<T> implements InvocationHandler {

  private volatile boolean initialized;

  private T delegate;

  public Object invoke(Object proxy, Method method, Object[] args)
      throws Throwable {
    try {
      // checking volatile field for synchronization
      Preconditions.checkState(initialized,
          "This is a proxy used to support"
              + " circular references. The object we're"
              + " proxying is not constructed yet. Please wait until after"
              + " injection has completed to use this object.");
      Preconditions.checkNotNull(delegate,
          "This is a proxy used to support"
              + " circular references. The object we're "
              + " proxying is initialized to null."
              + " No methods can be called.");

      // TODO: method.setAccessible(true); ?
      // this would fix visibility errors when we proxy a
      // non-public interface.
      return method.invoke(delegate, args);
    } catch (IllegalAccessException e) {
      throw new RuntimeException(e);
    } catch (IllegalArgumentException e) {
      throw new RuntimeException(e);
    } catch (InvocationTargetException e) {
      throw e.getTargetException();
    }
  }

  void setDelegate(T delegate) {
    this.delegate = delegate;
    initialized = true;
  }
}

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