新手学习socket编程，遇到问题，求大神帮忙！

//模拟转大写服务器，客户端输入小写字符串，服务器端进行处理，返回给客户端

//遇到的问题，第一次小写转大写可以，当进行第二次请求时候，就会出现错误(Connection refused: connect)

// 客户端

package cn;



import java.io.IOException;

import java.io.InputStream;

import java.io.OutputStream;

import java.net.Socket;

import java.net.UnknownHostException;

import java.util.Scanner;



public class Client {



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

		// TODO Auto-generated method stub

		

		while(true){

		System.out.println("请输入要转大写的英文字母：");

		Scanner scanner= new Scanner(System.in);

		String str=scanner.nextLine();

		

		//创建socket

		Socket socket= new Socket("127.0.0.1", 10004);

		//创建输出流输入流

		OutputStream outputStream=socket.getOutputStream();

		InputStream inputStream=socket.getInputStream();

		//输出给服务器端

		outputStream.write(str.getBytes());

		//接受服务器端发来的数据

		byte[]buf=new byte[1024];

		int len=inputStream.read(buf);

		System.out.println("转大写后"+(new String(buf,0,len)));

		}

	}



}

//服务器端

package cn;



import java.io.IOException;

import java.io.InputStream;

import java.io.OutputStream;

import java.net.ServerSocket;

import java.net.Socket;



public class Server {



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

		// TODO Auto-generated method stub



		ServerSocket serverSocket= new ServerSocket(10004);

		Socket socket=serverSocket.accept();

		System.out.println(socket.getInetAddress().getHostAddress()+"connecting.....");

		InputStream inputStream= socket.getInputStream();

		OutputStream outputStream = socket.getOutputStream();

		//读取客户端发来的数据

		byte[]buf=new byte[1024];

		int len=inputStream.read(buf);

		String str=new String(buf, 0, len);

		System.out.println(str);

		//逻辑处理

		String smallStr=str.toUpperCase();

		outputStream.write(smallStr.getBytes());

		socket.close();

		//serverSocket.close();

		}

	}