locateclient.java

本程序可在局域网内实现聊天、传送文件功能

package org.tuna.net.locate;

import java.io.*;
import java.net.*;
import java.nio.*;
import javax.swing.*;
import java.awt.event.*;
import java.nio.charset.*;
import org.tuna.util.PasswordCreator;

/**
 * 应用UDP协议，向局域网广播，
 * 若在超时间隔内接收到正确响应
 * 则数据来源IP即为服务器所在
 */
public abstract class LocateClient extends Thread
{
	private Timer timeoutMonitor;
	private int timeout;
	private String stopCode;
	private int stopCodeLen;
	private int activePort; /*发送定位信息的线程所使用的端口*/
	private InetAddress objectAddress;
	private int objectPort;
	private boolean stopCommand;


	/**
	 * 定义具有超时功能的定位器，若超时，则执行定位失败对应的方法
	 * @param to 超时间隔，单位为毫秒
	 */
	public LocateClient(int to)
	{
		stopCommand = false;
		timeout = to;
		timeoutMonitor = new Timer(timeout, new TimeoutListener());	
		timeoutMonitor.start();	
	}
	
	public LocateClient()
	{
		stopCommand = false;
	}
	
	
	// ------ For Thread ------
	public void run()
	{
		//得到用于停止定位线程的验证码，防止其它非法的停止命令
		stopCodeLen = DataField.LOCATE_STOP_CODE_LEN;
		PasswordCreator pc = new PasswordCreator(7, stopCodeLen);
		stopCode = pc.getPassword();		
		try{
		  DatagramSocket clientSocket = new DatagramSocket();
		  clientSocket.setSoTimeout(500);
		  activePort = clientSocket.getLocalPort();
		  InetAddress objectAddr = InetAddress.getByAddress(new byte[] {(byte)255,(byte)255,(byte)255,(byte)255});
		  byte[] sendData = NetCoder.encode(DataField.LOCATE_REQUEST);
		  DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, objectAddr, DataField.LOCATE_SERVER_PORT);		  
		  while(!stopCommand){
		    clientSocket.send(sendPacket);
		    byte[] receiveData = new byte[(DataField.LOCATE_INFO_LEN + stopCodeLen) * 4];
		    DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
		    try{
		      clientSocket.receive(receivePacket);
		    }
		    catch(SocketTimeoutException ex){  
		    	//注意此处不能打印错误信息
		    	receiveData[0] = (byte)-1;
		    }		    
		    if (receiveData[0] == (byte)-1) //接收失败
		       continue;
		    else{
		      String rcv = NetCoder.decode(receiveData).trim();      
		      if (rcv.length() < DataField.LOCATE_INFO_LEN)
		         continue;		    
		      //注意，这里有不安全性，容易发送同样信息进行欺骗		    
		      else if (rcv.substring(0, DataField.LOCATE_INFO_LEN).equals(DataField.LOCATE_RESPONSE)) {  
		        objectAddress = receivePacket.getAddress();
		        objectPort = receivePacket.getPort();	        
		        stopThread();
		        success();
		      }
		    }
		  }
		  clientSocket.close();
		}
		catch(Exception e){
			e.printStackTrace();
		}
	}
	
	
	// ------ Public Methods ------
	/**
	 * 定位失败后调用
	 */
	public abstract void fail();
	
	public InetAddress getObjectAddress()
	{
		return objectAddress;
	}
	
	public int getObjectPort()
	{
		return objectPort;
	}
	
	public int getTimeout()
	{
		return timeout;
	}
	
	public void stopThread()
	{
		stopCommand = true;
	}
		
	/**
	 * 定位成功后调用
	 */
	public abstract void success();
	

	// ------ Inner Class ------
	private class TimeoutListener implements ActionListener
	{
		public void actionPerformed(ActionEvent e){
			stopThread();
			timeoutMonitor.stop();
			fail();
		}
	}
	
	
	// ------ Test Method ------
	public static void main(String[] args)
	{
		//LocateClient lc = new LocateClient(2000);
		//lc.start();
	}
}