eventtracer.java

Java经典教程core java

/**
   @version 1.31 2004-05-10
   @author Cay Horstmann
*/

import java.awt.*;
import java.awt.event.*;
import java.beans.*;
import java.lang.reflect.*;

public class EventTracer
{
   public EventTracer()
   {
      // the handler for all event proxies
      handler = new
         InvocationHandler()
         {
            public Object invoke(Object proxy, Method method, Object[] args)
            {
               System.out.println(method + ":" + args[0]);
               return null;
            }
         };
   }

   /**
      Adds event tracers for all events to which this component
      and its children can listen
      @param c a component
   */
   public void add(Component c)
   {
      try
      {
         // get all events to which this component can listen
         BeanInfo info = Introspector.getBeanInfo(c.getClass());

         EventSetDescriptor[] eventSets = info.getEventSetDescriptors();
         for (EventSetDescriptor eventSet : eventSets)
            addListener(c, eventSet);
      }
      catch (IntrospectionException e) {}
      // ok not to add listeners if exception is thrown

      if (c instanceof Container)
      {
         // get all children and call add recursively
         for (Component comp : ((Container) c).getComponents())
            add(comp);
      }
   }

   /**
      Add a listener to the given event set
      @param c a component
      @param eventSet a descriptor of a listener interface
   */
   public void addListener(Component c, EventSetDescriptor eventSet)
   {
      // make proxy object for this listener type and route all calls to the handler
      Object proxy = Proxy.newProxyInstance(null,
         new Class[] { eventSet.getListenerType() }, handler);

      // add the proxy as a listener to the component
      Method addListenerMethod = eventSet.getAddListenerMethod();
      try
      {
         addListenerMethod.invoke(c, proxy);
      }
      catch(InvocationTargetException e) {}
      catch(IllegalAccessException e) {}
      // ok not to add listener if exception is thrown
   }

   private InvocationHandler handler;
}