Socket server that waits for message from client to read

Question

I have the following socket server in java,

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;

public class MiddleSocket {
    private ServerSocket middleman;
    private int port = 1027;
    private Socket client;


    protected void createSocketServer()
    {
        try
        {
            middleman = new ServerSocket(port);
            client = middleman.accept();
            middleman.close();
            PrintWriter out = new PrintWriter(client.getOutputStream(),true);
            BufferedReader in = new BufferedReader(new InputStreamReader(client.getInputStream()));
            BufferedReader stdIn = new BufferedReader(new InputStreamReader(System.in));
            while(true)
            {
                System.out.println("echo: " + in.readLine());
                out.println("test");
            }
        }
        catch(IOException e)
        {
            System.out.println(e);
        }
    }

}

It works correctly in how it reads from the client and everything. However, I want the socket server to only try and read when there is a message from the client since in the loop it keeps reading even when no messages from the client are received this outputs a bunch of

echo: null

Is there some mechanism short of a wait() to have the while loop to know to just sit and wait and then fire when a message is sent from the client to read that message and once that message is read and a reply is sent, to then just sit idle until the next message from the client is received?

Answer 1

You can simply do something like as follows:

String line;
while ((line = in.readLine()) != null) {
   \\Do stuff
}

This should have the expected behaviour.

Edit:

here's a full example of what I was talking about in the comments using your code:

package javaapplication12;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;

public class SocketExample {
    private ServerSocket middleman;
    private int port = 8080;
    private Socket client;


    protected void createSocketServer()
    {
        try
        {
            while (true){
                middleman = new ServerSocket(port);
                client = middleman.accept();
                middleman.close();
                PrintWriter out = new PrintWriter(client.getOutputStream(),true);
                BufferedReader in = new BufferedReader(new InputStreamReader(client.getInputStream()));
                BufferedReader stdIn = new BufferedReader(new InputStreamReader(System.in));
                String line;
                while((line = in.readLine()) != null)
                {
                    System.out.println("echo: " + line);
                    out.println("test");
                }
            }
        }
        catch(IOException e)
        {
            System.out.println(e);
        }
    }

    public static void main(String[] args){
        SocketExample test = new SocketExample();
        test.createSocketServer();
    }
}