methoddispatcher.java

移动Agent编程IBM开发的移动Agent编程工具Aglet 采用纯Java编写可移植性好这是用它写的一些例子用于初级入门

/*
 * @(#)MethodDispatcher.java
 *
 * 03L7246 (c) Copyright IBM Corp. 1996, 1998
 *
 * The program is provided "as is" without any warranty express or
 * implied, including the warranty of non-infringement and the implied
 * warranties of merchantibility and fitness for a particular purpose.
 * IBM will not be liable for any damages suffered by you as a result
 * of using the Program. In no event will IBM be liable for any
 * special, indirect or consequential damages or lost profits even if
 * IBM has been advised of the possibility of their occurrence. IBM
 * will not be liable for any third party claims against you.
 */

package examples.mdispatcher;

import com.ibm.aglet.*;

import java.io.*;
import java.lang.reflect.*;
import java.util.Hashtable;

/**
 * MethodDispatcher class binds a message and a corresponding method.
 * All methods which has a signature <tt> method(Message msg); </tt>
 * are binded and invoked when it receives the corresponding message.
 * <pre>
 *    MethodDispatcher mdispatcher = null;
 *    public void onCreation(Object obj){ 
 *        mdispatcher = new MethodDispatcher(this);
 *    }
 *
 *    pubic boolean handleMessage(Message m) {
 *        return mdispatcher(m);
 *    }
 *
 *    // This method is called when the message("doJob") is sent to the aglet.
 *    public void doJob(Message m) {
 *        // do your job.
 *    }
 * </pre>
 * This may be incorporated with MessageManager in the future.
 *
 * @version     1.00	$Date: 1999/10/27 05:16:39 $
 * @author	Mitsuru Oshima
 */
public class MethodDispatcher implements Serializable {

    private static Class TYPE = null;
    private Object target;

	static {
	try {
		TYPE = Class.forName("com.ibm.aglet.Message");
	} catch (Exception ex) {
        	System.out.println(ex);
	}
    }

    transient Hashtable method_table = new Hashtable();

    public MethodDispatcher(Object a) {
		target = a;
		makeTable();
    }

    public boolean handleMessage(Message msg) {
		Method m = (Method)method_table.get(msg.getKind());
		if (m != null) {
	    	try {
				Object args[] = new Object[1];
				args[0] = msg;
				m.invoke(target, args);
	    	} catch (IllegalAccessException ex) {
				// should not happen
				return false;
	    	} catch (IllegalArgumentException ex) {
				// should not happen
				return false;
	    	} catch (InvocationTargetException ex) {
				// if the exception is thrown in the method
				try {
		    		if (ex.getTargetException() instanceof Exception) {
						msg.sendException((Exception)ex.getTargetException());
		    		} else {
						// temporary
						msg.sendException(ex);
		    		}
		    		// shold not happen
				} catch (IllegalAccessError exx) {
		    	// if a reply has already been sent.
				}
				return false;
	    	}
	    	return true;
		}
		return false;
	}

    private void writeObject(ObjectOutputStream s) 
    						throws IOException{
		s.writeObject(target);
    }

    private void readObject(ObjectInputStream s)
         					throws IOException, ClassNotFoundException{
		target = (Aglet)s.readObject();
		makeTable();
    }

    void makeTable() {
		method_table = new Hashtable();
		Class clazz = target.getClass();
		Method methods[] = clazz.getMethods();

		for(int i=0; i<methods.length; i++) {
	    	Method m = methods[i];

	    	Class[] types = m.getParameterTypes();

	    	//
	    	// select the method whose signature is like
	    	// type method(Message msg);
	    	//
	    	if (types.length ==1 && types[0] == TYPE &&
	        	Modifier.isPublic( m.getModifiers() ) ) {
	        	method_table.put(m.getName(), m);
	    	}
		}
    }
}