如何在Java的客户端-服务器应用程序中读写多行

Question

我有一个多线程的Java客户端-服务器应用程序，发现自己与多线程通信的斗争。这是我的意思

如果我这样写一个服务器：

private static void startHandler(final Socket socket)
    {
        Thread thread = new Thread()
        {
            @Override
            public void run()
            {
                try {
                    Scanner inputFromUser = new Scanner(socket.getInputStream());
                    PrintStream outPutToUser = new PrintStream(socket.getOutputStream(), true);
                    outPutToUser.println("Welcome!");
                    System.out.println(inputFromUser.nextLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        };
        thread.start();

    }

并这样编写客户端：

public static void main(String[] args) throws Exception
    {
        Scanner inputFromUser = new Scanner(System.in);
        Socket socket = new Socket("127.0.0.1", 5555);
        Scanner inputFromServer = new Scanner(socket.getInputStream());
        PrintStream outputToServer = new PrintStream(socket.getOutputStream());
        String greetingFromServer = inputFromServer.nextLine();
        System.out.println(greetingFromServer);
        outputToServer.println(inputFromUser.nextLine());
    }

它运作得很好：

>

服务器向客户端发送“欢迎”

用户输入一些字符串

在服务器控制台中打印该字符串

但如果我试图让它变得更复杂，就像这样：

private static void startHandler(final Socket socket)
    {
        Thread thread = new Thread()
        {
            @Override
            public void run()
            {
                try {
                    Scanner inputFromUser = new Scanner(socket.getInputStream());
                    PrintStream outPutToUser = new PrintStream(socket.getOutputStream(), true);
                    outPutToUser.println("Welcome!");
                    sendInitialCommandsToUser(outPutToUser);
                    System.out.println(inputFromUser.nextLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        };
        thread.start();

    }

    private static void sendInitialCommandsToUser(PrintStream writer)
    {
        writer.println("1 - Log In");
        writer.println("2 - Sign up");
        writer.println("3 - Exit");
    }

客户：

public static void main(String[] args) throws Exception
    {
        Scanner inputFromUser = new Scanner(System.in);

        Socket socket = new Socket("127.0.0.1", 5555);
        Scanner inputFromServer = new Scanner(socket.getInputStream());
        PrintStream outputToServer = new PrintStream(socket.getOutputStream());

        String greetingFromServer = inputFromServer.nextLine();
        System.out.println(greetingFromServer);

        getMultipleLinesFromServer(inputFromServer);

        outputToServer.println(inputFromUser.nextLine());
    }

    private static void getMultipleLinesFromServer(Scanner scanner)
    {
        while(scanner.hasNextLine())
        {
            System.out.println(scanner.nextLine());
        }
    }

它被堆放在GetMultipleLinesFromServer（Scanner Scanner)方法上

客户端输出仅

Welcome!
1 - Log In
2 - Sign up
3 - Exit

我无法提供要在服务器上打印的字符串..有什么问题？

Answer 1

如果您查看扫描器hasNextLine方法的Javadocs...

 Returns true if there is another line in the input of this scanner.
 This method may block while waiting for input. The scanner does not
 advance past any input.

似乎一旦它打印了“3-exit”，它就会阻塞以等待来自服务器的更多数据。

Answer 2

如果希望按行读取，BufferedReader是一个不错的选择

试试这个，对我的主意很管用

package com.zhouplus;

import java.io.*;
import java.net.ServerSocket;
import java.net.Socket;

public class Server {

    private static void startHandler(final Socket socket) {
        Thread thread = new Thread(() -> {
            try {
                BufferedReader inputFromUser = new BufferedReader(new InputStreamReader(socket.getInputStream()));
                PrintWriter outPutToUser = new PrintWriter(new OutputStreamWriter(socket.getOutputStream()));
                outPutToUser.println("Welcome!");
                sendInitialCommandsToUser(outPutToUser);
                System.out.println("start readline!");
                System.out.println(inputFromUser.readLine());
            } catch (IOException e) {
                e.printStackTrace();
            }
        });
        thread.start();
    }

    private static void sendInitialCommandsToUser(PrintWriter writer) {
        writer.println("1 - Log In");
        writer.println("2 - Sign up");
        writer.println("3 - Exit");
        writer.flush();
    }

    public static void main(String[] argv) throws IOException {
        ServerSocket ss = new ServerSocket(5555);
        Socket accept = ss.accept();
        startHandler(accept);
    }
}

和客户端

package com.zhouplus;

import java.io.*;
import java.net.Socket;
import java.util.Scanner;

public class Client {
    public static void main(String[] args) throws Exception {
        Scanner inputFromUser = new Scanner(System.in);

        Socket socket = new Socket("localhost", 5555);
        BufferedReader inputFromServer = new BufferedReader(new InputStreamReader(socket.getInputStream()));
        PrintWriter outputToServer = new PrintWriter(socket.getOutputStream());


        String greetingFromServer = inputFromServer.readLine();
        System.out.println(greetingFromServer);

        new Thread(() -> {
            String str = inputFromUser.nextLine();
            outputToServer.println(str);
            outputToServer.flush();
        }).start();

        getMultipleLinesFromServer(inputFromServer);
    }

    private static void getMultipleLinesFromServer(BufferedReader br) throws IOException {
        String str;
        while ((str = br.readLine()) != null) {
            System.out.println(str);
        }
        System.out.println("over");
    }
}