Question

我正在尝试用Java实现多线程服务器聊天应用程序该程序创建了一个线程并等待客户端连接。连接客户端后，它会创建另一个线程并等待另一个客户端连接。

这是我的ChatServer.java

package com.chat.server;



import java.io.InputStream;
import java.io.IOException;
import java.net.Socket;
import java.net.InetAddress;
import java.net.ServerSocket;



/**
 * <p>The chat server program</p>
 * This class is a Thread that recieves connection
 * from different clients and handles them is separate
 * Thread.
 *
 * @author Aditya R.Singh
 * @version 1.0.0
 * @since 1.0.0
 */
class ChatServer extends Thread {

    private int port;                    // The port number to listen at.
    private String ip;                   // To store the IP address.
    private Socket socket;               // Socket connection with different clients.
    private InetAddress inet;            // Handling Client Address.
    private ServerSocket serverSocket;   // The server socket used by clients to connect.



    /**
     * This is solely intended for instantiation purpose.
     * 
     * @param PORT - The port number to listen for client requests
     */
    ChatServer(final int PORT) {


        /* Initiallizing all instance variables to null. */
        ip = null;
        inet = null;
        socket = null;
        serverSocket = null;

        /* Initiallizing the port number. */
        port = PORT;
    }



    /**
     * This method creates a connection between server and client.
     * 
     * @throws java.io.IOException
     */
    private void createConnection() throws IOException {

        serverSocket = new ServerSocket(port);  // Listen to the required port. 
        socket = serverSocket.accept();         // Accept the client connection.
    }



    /**
     * This method sets the IP address.
     */
    private void setIP() {

        inet = socket.getInetAddress();
        ip = new String(inet.getHostAddress());
    }



    /**
     * This method returns the IP address.
     *
     * @return IP address.
     */
    public String getIP() {

        return ip;
    }



    /**
     * This method checks if the socket has been connected
     * with any client.
     *
     * @return True if the client has been connected, else false
     */
    public boolean isConnected() {

        if(socket == null)
            return false;
        return true;
    }



    /**
     * This method returns the InputStream
     * from the Socket.
     * 
     * @return InputStream if Socket has been connected to the client, else null
     * @see java.io.InputStream
     */
    public InputStream getInputStream() throws IOException {

        if(socket == null)
            return null;
        return socket.getInputStream();
    }



    @Override
    public void run() {

        try {

            createConnection();
            setIP();
        } catch(IOException exception) {

            exception.printStackTrace();
        }
    }
}

这是我的Server.java：

package com.chat.server;



/** 
 * <p>The Server app</p> 
 * This is the controller for accepting connections.
 *
 * @author Aditya R.Singh 
 * @version 1.0.0
 * @since 1.0.0
 */
public class Server {


    /**
     * The port at which clients will connect.
     */
    public static final int PORT = 6005;          



    /**
     * For instantiation purpose.
     */
    public Server() {


    }



    public static void main(String[] args) {


        /* Keep accepting connections. */
        while(true) {

            ChatServer chat = new ChatServer(PORT); // Connecting port.
            chat.start();

            while(!chat.isConnected())
                /* This is a false loop. Intended to keep running unless another client is not requesting to connect. */;

            System.out.println("We connected to: "+chat.getIP());   
        }
    }
}

代码编译得很好在运行代码时：

java com.chat.server.Server

似乎该程序正在侦听客户端进行连接。但是在连接到客户端之后，它应该打印客户端的IP地址，然后为另一个客户端创建另一个线程。但它不会打印客户端的IP。

这是我的Client.java：

package com.chat.client;



import java.net.Socket;
import java.io.IOException;



public class Client {

    public static void main(String[] args) {

        Socket socket = null;


        try {

            socket = new Socket("127.0.0.1", 6005);
            System.out.println("Socket connected.");
        } catch(IOException ex) {

            ex.printStackTrace();
        }
    }
}

客户端连接到服务器，必须打印Socket connected。客户这样做。客户端工作正常：

java com.chat.client.Client  
Socket connected.

但服务器应用程序不会打印客户端的IP地址。为什么这样？

Answer 1

这是竞争条件。行socket = serverSocket.accept();导致while(!chat.isConnected())循环在调用方法'setIP（）'之前终止。验证这是导致问题的原因的一种快速方法是更改此方法：

public boolean isConnected() {
    if(socket == null)
        return false;
    return true;
}

到

public boolean isConnected() {
    if(socket == null || ip == null)
        return false;
    return true;
}

为了解决问题，您应该确保设置IP的代码和检查其连接的代码是否使用synchronized关键字。另外，请注意while(!chat.isConnected())循环没有暂停，这意味着它需要尽可能多的CPU ...这绝对不是好事。

查看@Michael Petch为正确实施聊天服务器而发布的链接。

Answer 2

这不是完整的代码

package demo;

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



public class MultithreadedServer {

    public static final int PORT = 10000;

    public static void main(String[] args) {
        try(ServerSocket server = new ServerSocket(PORT)) {
            while(true){
                Socket connection = server.accept();
                Thread client = new ClientThread(connection);
                client.start();
            }
        } catch (IOException ex) {
            System.out.println("Error start server");
        }
    }

}

class ClientThread extends Thread {
    private Socket connection;

    public ClientThread(Socket connection) {
        this.connection = connection;
    }

    @Override
    public void run(){
        //Do communication with client
    }

}

创建多线程Java服务器聊天应用程序。

2 个答案: