setproxyexample.java

java 完全探索的随书源码

import java.lang.reflect.*;
import java.util.*;
/*
 * Implement InvocationHandler to turn on and off the ability
 * to disable the methods in Set that remove elements from the
 * collection
 */
class DisallowRemoveSet implements InvocationHandler {
  private Set delegate;
  private boolean disallowRemove = true;

  public DisallowRemoveSet(Set delegate) {
    this.delegate = delegate;
  }

  public void setDisallowRemove(boolean disallowRemove) {
    this.disallowRemove = disallowRemove;
  }

  public Object invoke( Object proxy, Method meth, Object[] args )
    throws Throwable {
    if ( disallowRemove && (meth.getName().startsWith("remove") ||
     meth.getName().equals("retainAll") || meth.getName().equals("clear")) ) {
      // trying to remove when the option is disabled
      throw new UnsupportedOperationException(
        "Set does not allow element removal");
    }
    // method call okay, send it on to the delegate Set implementation
    return meth.invoke(delegate, args);
  }
}

public class SetProxyExample {
  public static void main(String[] args) {
    Set delegate = new HashSet();
    Class[] setInterface = new Class[] { Set.class };
    DisallowRemoveSet handler = new DisallowRemoveSet(delegate);

    // create a proxy that wraps a HashSet implementation of the Set
    // interface with a DisallowRemoveSet
    Set setProxy = (Set)Proxy.newProxyInstance( Thread.currentThread().
      getContextClassLoader(), setInterface, handler );

    // build a set with 5 elements
    String[] data = new String[] {"A","B","C","D","E"};
    setProxy.addAll( Arrays.asList(data) );

    try {
      System.out.println("Enable removes and call for first data entry");
      handler.setDisallowRemove(false);
      setProxy.remove( data[0] );

      handler.setDisallowRemove(true);
      System.out.println("Disable removes and call for second data entry");
      setProxy.remove( data[1] );
    }
    catch (UnsupportedOperationException e ) {
      System.out.println("Exception thrown: " + e.getMessage());
    }
  }
}