SOCKET程序出现错误，自动关闭怎么回事？

程序如下：
import java.io.*;
import java.net.*;
import java.applet.*;
public class TalkServer
{

public static void main(String args[])
{
try
{
ServerSocket server=null;
try{server=new ServerSocket(4700);}
catch(Exception e){System.out.println("can not listen to:"+e);}
Socket socket=null;

try{socket=server.accept();}
catch(Exception e){System.out.println("Error:"+e);}

BufferedReader is=new BufferedReader(new InputStreamReader(socket.getInputStream()));
//BufferedReader sin=new BufferedReader(new InputStreamReader(System.in));
String line=is.readLine();

while(!line.equals("bye")){
System.out.println("Client:"+line);
line=is.readLine();}

if(line.equals("bye")){
System.out.println("the socket will be closed");
//sin.close();
is.close();
socket.close();
server.close();}
}catch(Exception e){System.out.println("Error:"+e);}

}
}
请问各位高手：当客户端发过来数据后，就回出现出错误，并且自动关闭了SOCKET怎么回事呢？
谢谢，我是新手！