udp实现聊天室通信发消息长度不对？？

[狮猿]

聊天室部分程序是这样的：
LoginWindow.java里调用：
SendContentThread.java
ReceiveContentThread.java
就是JTextField响应事件 发送内容

tf.addActionListener(
				new ActionListener()
				{
					public void actionPerformed(ActionEvent e)
					{
						Thread sct=new Thread(new SendContentThread(tf,username));
						sct.start();
						Thread rct=new Thread(new ReceiveContentThread(ta,port));
						rct.start();
					}
				}

			);

public class SendContentThread implements Runnable{


	JTextField tf;
	String username;
	
	public SendContentThread(JTextField tf, String username) {
		this.tf=tf;
		this.username=username;
		// TODO Auto-generated constructor stub
	}
	@Override
	public void run() {
		// TODO Auto-generated method stub
		try {
			DatagramSocket ds=new DatagramSocket();
			
			InetAddress ia=InetAddress.getLocalHost();
			
			Properties pro=new Properties();
			pro.load(new FileInputStream("F:\\codeJava\\ChatRoom_U\\src\\list.properties"));
			
			Set keySet=pro.keySet();//key的集合
			
			Iterator iter=keySet.iterator();
			
		
			while(iter.hasNext())
			{
				String alreadyName=(String)iter.next();//每次循环就能拿到一个key
				int port=Integer.parseInt(pro.getProperty(alreadyName));//端口
				String string=username+":"+tf.getText();
				
				byte by1[]=string.getBytes();
				DatagramPacket dp=new DatagramPacket(by1,string.length());
				
				
				dp.setAddress(ia);
				dp.setPort(port);//端口不能固定
				ds.send(dp);
				
			}
			tf.setText("");
		} catch (SocketException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (UnknownHostException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (FileNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		
	}

}

public class ReceiveContentThread implements Runnable{

	
	JTextArea ta;
	int port;
	
	public ReceiveContentThread(JTextArea ta, int port) {
		// TODO Auto-generated constructor stub
		this.ta=ta;
		this.port=port;
		
	}
	@Override
	public void run() {
		// TODO Auto-generated method stub
		
		try {
			byte by[]=new byte[1024];
			DatagramPacket dp=new DatagramPacket(by,by.length);
			DatagramSocket ds=new DatagramSocket(port);
			
			while(true)
			{
				System.out.println("等消息......");
				ds.receive(dp);
				String str=new String(by);
				System.out.println("收到消息："+str);
				ta.setText(str+"\n");
				
			}
		} catch (SocketException e) {
			// TODO Auto-generated catch block
			//e.printStackTrace();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

}

结果是
如果输入sssssssssssssssssss 会成功
但是下一行如果输入比上一句长度小结果会出现不对
比如输入f 会出现
fsssssssssssssssssss
我觉得长度可能获取的还是上一句的。。。
？？？怎么解决？？

[墨笙弘一]

多线程不擅长啊