之前也出想过问题，就是连接以后，不能进行输出输入了（不能互相通信，但是连接上了）。大神们帮忙看看是什么问题，小弟谢过啦！！！！！

import java.io.*;
import java.net.*;

/**
 * 服务端类
 * */
public class ServerStart {


    public static void main(String[] args){
        ServerSocket server = null;
        try{
        //1.建立连接
            server = new ServerSocket(9000);
            while(true){                
                Socket client = server.accept();
                System.out.println("建立连接");
        //2.获取流对象
                ObjectInputStream in = new ObjectInputStream(client.getInputStream());
                ObjectOutputStream out = new ObjectOutputStream(client.getOutputStream());
                BufferedReader ins = new BufferedReader(new InputStreamReader(System.in));
        //3.传输数据
                while(true){
                    String flag = (String)in.readObject();
                    System.out.println("客户端说："+flag);  
                    if(flag == null){
                        break;
                    }
                    String str = ins.readLine();
                    out.writeObject(str);
                    out.flush();
                }
                    
            
        //4.关闭流
                client.close();
                in.close();
                out.close();
            }
        }catch(Exception e){
            e.getStackTrace();
        }
    }
    
}
import java.io.*;
import java.net.Socket;
/**
 * 客户端类
 * */
public class ClientStart {

    public void isNameExist(){
        Socket client = null;
        try{
        //1.建立连接
            client = new Socket("127.0.0.1",9000);
        //2.获取流对象
            ObjectInputStream in = new ObjectInputStream(client.getInputStream());
            ObjectOutputStream out = new ObjectOutputStream(client.getOutputStream());
            BufferedReader ins = new BufferedReader(new InputStreamReader(System.in)); 
        //3.传输数据
            while(true){
                String str = ins.readLine();
                out.writeObject(str);
                out.flush();
                if(str == ""||str.equals("exit")){
                    break;
                }
                String flag = (String)in.readObject();
                System.out.println("服务器说："+flag);
            }
                
        }catch(Exception e ){
            e.getStackTrace();

        }finally{
            //4.关闭流
            try {
                client.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            
        }
    }
    public static void main(String[] args){
        ClientStart c = new ClientStart();
        c.isNameExist();
    }

}