发送/接收的套接字错误

Question

If I send a message, it will only be printed out by the server if I run it in a loop.

I tried to send the message after 1 minute, send it 50 times, but nothing will print it out on the server side.

What is my error?

Here is my code, it was written in Netbeans:

package me.jackboyplay.sockets_client;

import java.io.DataInputStream;
import java.io.IOException;
import java.io.PrintWriter;
import java.net.Socket;
import java.util.concurrent.TimeUnit;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 *
 * @author JackboyPlay
 */
public class Client {

    public static void main(String[] args) throws IOException {
        Socket socket = null;
        try {
            socket = new Socket("localhost", 5001);
        } catch (IOException ex) {
            Logger.getLogger(Client.class.getName()).log(Level.SEVERE, null, ex);
        }
        if(socket == null){
            return;
        }
        DataInputStream dis = null;
        PrintWriter dos = null;
        try {
            dis = new DataInputStream(socket.getInputStream());
            dos = new PrintWriter(socket.getOutputStream());
        } catch (IOException ex) {
            Logger.getLogger(Client.class.getName()).log(Level.SEVERE, null, ex);
        }
        int x = 0;
        Long l = System.currentTimeMillis() + TimeUnit.SECONDS.toMillis(5);
        for(int i = 0; i < 50; i++){
            dos.write("X: " + i);
        }
    }

}

package me.jackboyplay.jc_cloudsystem.mechaniken;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 *
 * @author JackboyPlay
 */
public class SocketClient extends Thread {

    private Socket socket;

    public SocketClient(Socket socket){
        this.socket = socket;
        System.out.println("Ein Client wurde akzeptiert.");
    }

    @Override
    public void run() {
        BufferedReader br;
        PrintWriter pw;
        try {
            br = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            pw = new PrintWriter(socket.getOutputStream());

            while(true){
                String line = br.readLine();
                System.out.println(line);
            }

        } catch (IOException ex) {
            Logger.getLogger(SocketClient.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

}

Class 1 is the Client that sends a message to the server.

Class 2 is the Server that will print out the message.

Answer 1

The server is using BufferedReader.readLine() , but the client is not sending any line breaks, so readLine() never returns:

Reads a line of text. A line is considered to be terminated by any one of a line feed ('\\n'), a carriage return ('\\r'), or a carriage return followed immediately by a linefeed.

The client should be using PrintWriter.println() instead of PrintWriter.write() :

Terminates the current line by writing the line separator string. The line separator string is defined by the system property line.separator , and is not necessarily a single newline character ('\\n').

dos.println("X: " + i);

Prints a String and then terminates the line. This method behaves as though it invokes print(String) and then println() .

Alternatively, use PrintWriter.print() to write the values as needed, and then call PrintWriter.println() when finished:

dos.print("X: ");
dos.print(i);
dos.println();

Either way, you may also need to call PrintWriter.flush() to actually send the output over the wire:

dos.flush();