Java BufferedReader reading form socket doesn't return null

问题

I'm currently writing an app in Java that opens a socket and should receive and send data over it.

It is my understanding that BufferedReader.readLine() returns null once the buffer is empty. However, my code doesn't exit from the loop that reads the lines from the BufferedReader. The idea is thata i receive a list of songs and then send a value to the server where a song starts playing.

This is the code:

package me.frankvanbever.MediaServerClient;

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

        public class MediaServerClient {

            /**
             * @param args
             */
            public static void main(String[] args) {

                    Socket server;
                    try {
                        server = new Socket( "10.42.0.41" , 2626 );

                        InputStream in = server.getInputStream();
                        OutputStream out = server.getOutputStream();

                        BufferedReader bin = new BufferedReader( new InputStreamReader( in ) , 4096);

                        String inputline;
                        while( (inputline = bin.readLine()) != null){

                            System.out.println(inputline);

                        }

                        System.out.println("exited loop");
                        out.write('1');
                    } catch (UnknownHostException e) {
                    } catch (IOException e) {
                    }


            }

    }

Is this normal behaviour? The server is written in python and I can change the source code.

回答1:

It is my understanding that BufferedReader.readLine() returns null once the buffer is empty.

No. It will return null once the underlying return has been closed. If the server you're connecting to doesn't close the connection, BufferedReader will just hang, waiting for the next line of text.

Don't forget that TCP is stream-oriented (as is BufferedReader). There's no indication of "a complete message" unless you put it in your protocol. That's why protocols often include things like message terminators, or they specify how much data is in a message before sending it.

来源：https://stackoverflow.com/questions/16384186/java-bufferedreader-reading-form-socket-doesnt-return-null

标签

java

sockets

bufferedreader