为什么我没有从TCP服务器和客户端收到任何消息？

Question

I am trying to implement a TCP Server and Client in Java. The Client should send a message to the Server and the Server should send the same message back to the Client. I get the connection between both, but there is not any message. I have already searched a lot in the internet and my code is so simliar to other code, but my solution is still not working. I am pretty new to this topic so I am happy about every advice. Here is my Client code:

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.net.Socket;

public class Client 
{
    public static void main(String[] args) 
    {
    final int PORT = 5000;
    Socket socket = null;
    try
    {
        socket = new Socket("localhost", PORT);
        OutputStream os = socket.getOutputStream();
        BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(os));
        String message = "Hello World";
        bw.write(message);
        bw.flush();

        InputStream is = socket.getInputStream();
        BufferedReader br = new BufferedReader(new InputStreamReader(is));
        String echo = br.readLine();
        System.out.println(echo);
    }
    catch (Exception e)
    {
        e.printStackTrace();
    }
    finally
    {
        try
        {
        socket.close();
        } catch (IOException e)
        {
        e.printStackTrace();
        }
    }
    }
}

Server code:

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.net.ServerSocket;
import java.net.Socket;

public class Server
{
    public static void main(String[] args)
    {
        final int PORT = 5000;
        ServerSocket serverSocket = null;
        Socket socket = null;
        try
        {
            serverSocket = new ServerSocket(PORT);
            socket = serverSocket.accept();
            InputStream is = socket.getInputStream();
            BufferedReader br = new BufferedReader(new 
            InputStreamReader(is));
            String message = br.readLine();
            System.out.println(message);
            OutputStream os = socket.getOutputStream();
            BufferedWriter bw = new BufferedWriter(new 
            OutputStreamWriter(os));
            bw.write("ECHO: " + message);
            bw.flush();
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }
        finally
        {
            try
            {
                serverSocket.close();
            } catch (IOException e)
            {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }



    }
}

Answer 1

It's because you're using readLine() to receive the message and you never terminate the message with an end of line .

Add a new line to your messsage and the readLine() method will see it and return a value to you. String message = "Hello World\\n";

Note you're going to have the same problem on the return path, because you're also using readLine() on the client. Add a new line to the server's reply: bw.write("ECHO: " + message + '\\n');