java server端利用socket和多线程技术实现消息转发功能，求帮助！

package com.zeph.multiclient;



import java.io.BufferedReader;

import java.io.BufferedWriter;

import java.io.IOException;

import java.io.InputStreamReader;

import java.io.OutputStreamWriter;

import java.net.ServerSocket;

import java.net.Socket;



public class MultiThreadServer extends Thread {

    private Socket client;



    public MultiThreadServer(Socket c) {

        this.client = c;//创建与客户端连接的socket

    }



    public void run() {

        try {

            System.out.println(Thread.currentThread().getName() + " start");

            BufferedReader in = new BufferedReader(new InputStreamReader(client.getInputStream()));

            //利用BufferedReader实现数据的快速接收,getInputStream()获取socket底层数据输入流，InputStreamReader()实现字节到字符串的高校读取

            BufferedWriter out =new BufferedWriter(new OutputStreamWriter(client.getOutputStream()));

            //利用BufferedWriter实现数据的快速写入，getOutputStream()获取socket底层数据输出流，OutputStreamWriter()实现字节到字符串的高校写入

            String str = in.readLine();//此方法为阻塞状态，一直到收到回车(\r)换行(\n)才结束阻塞(接收信息完毕)

            while (str != null) {

                System.out.println("server receive: " + str);//将接收到的信息打印出来

                out.write('3');//信息写入输出流

                out.flush();//写回client需要flush

                System.out.println("send ok");

                str = in.readLine();//读取client返回信息，此方法为阻塞状态，一直到收到回车(\r)换行(\n)才结束阻塞(接收信息完毕)

                System.out.println("server receive: " + str);

                str = null;//清空数据，跳出循环

            }

            System.out.println(Thread.currentThread().getName() + " end");

            out.close();

        } catch (IOException e) {

        }

    }



    public static void main(String[] args) throws IOException {

        ServerSocket server = new ServerSocket(1234);

        System.out.println("server is start!");

        while (true) {

            MultiThreadServer mc = new MultiThreadServer(server.accept());

            if(server.getInetAddress().getHostAddress().indexOf("0.0.0.0")<0){

            	System.out.println("accept connect: " + server.getInetAddress().getHostAddress());

            }     

            mc.start();

        }

    }

}