消息未从服务器发送到单个服务器中的客户端-Java中的多个客户端

Question

I am coding for a single server and multiple client in JAVA . This is my code for server And This is my code for client .

More specifically , I have the following code in my server .

String Name;
    try {
         os.println("Enter Your Name:");
        Name=is.readLine();
        os.println("Hello "+ Name +" Welcome To Our Exam System.Please type Exam to take an Exam or type QUIT to Exit");
         line=is.readLine();
        while(line.compareTo("QUIT")!=0){

            os.println(line);
            os.flush();
            System.out.println("Response to Client  :  "+line);
            line=is.readLine();
        }   
    } catch (IOException e) {

        line=this.getName(); //reused String line for getting thread name
        System.out.println("IO Error/ Client "+line+" terminated abruptly");
    }
    catch(NullPointerException e){
        line=this.getName(); //reused String line for getting thread name
        System.out.println("Client "+line+" Closed");
    }

ANd the following code in client.java

 try {
        s1=new Socket(address, 4445); // You can use static final constant PORT_NUM
        br= new BufferedReader(new InputStreamReader(System.in));
        is=new BufferedReader(new InputStreamReader(s1.getInputStream()));
        os= new PrintWriter(s1.getOutputStream());
    }
    catch (IOException e){
        e.printStackTrace();
        System.err.print("IO Exception");
    }

    System.out.println("Client Address : "+address);
    System.out.println("Enter Data to echo Server ( Enter QUIT to end):");

    String response=null;

    try{
         response=is.readLine();
         System.out.println(response);
        line=br.readLine(); 
         os.println(line);
         response=is.readLine();
        line=br.readLine();   
        while(line.compareTo("QUIT")!=0)
        {
            os.println(line);
            os.flush();
            response=is.readLine();
            System.out.println("Server Response : "+response);
            line=br.readLine(); 
        }

    }
    catch(IOException e){
        e.printStackTrace();
    System.out.println("Socket read Error");
    }

From this code I am expecting the following task :

1. Initially A connection has been established between server and client
2. A message will be sent from server to client named "Enter your name"
3. This msg will be printed in clients console .
4. From client , a name will be sent to server .

5. Then server will do the following line : os.println("Hello "+ Name +" Welcome To Our Exam System.Please type Exam to take an Exam or type QUIT to Exit");

6. But after establishment of connection , no message like " Enter your name " is sent from server to client

Why ?

Answer 1

Add the following line after Server, LINE 68:

• os.flush()

the client will show the expected "Enter your name".

Both server and client are waiting for input, thus sitting in a deadlock. You must call os.flush() to actually sed your data to the server.

Your server code writes to output but doesn't send it:

• Server, LINE 68: os.println("Enter Your Name:");

Then the client hangs because the server didnt send it via os.flush() at:

• Client, LINE 37: response = is.readLine();

while your server is also waiting for the clients answer at

• Server, LINE 69: Name = is.readLine();

Source for the os.flush command was this sample code: https://stackoverflow.com/a/5680427/3738721