创建一个对象，将该对象传递给另一个对象的构造函数，在对象上调用 wait()，然后在 Java 中调用 notification()

Question

我正在尝试处理服务器同一端口上的多个连接。我通过实例化一个对象并将其传递到另一个实现 Runnable 的类的构造函数来实现此目的。然后，我在 Runnable 类中设置一个套接字，并在客户端连接到端口后对传递的对象调用 notification()。然后，这应该允许服务器重新启动其循环，在收到通知后创建 Runnable 类的另一个实例。但是，目前直到客户端关闭后才会到达 wait()。以下是我拥有的 3 个相关类：

服务器类：

   package server;

import java.io.IOException;
import java.net.ServerSocket;
import java.util.HashMap;

public class Server {

    public static void main(String[] args){
        HashMap<String, PortDummy> portDummies = new HashMap<String, PortDummy>();
        ServerSocket serverSocket = null;
        try {
            serverSocket = new ServerSocket(8000);
        } catch (IOException e1) {
            e1.printStackTrace();
        }

        for(;;){
            Object block = new Object();
            PortDummy dummy = new PortDummy(serverSocket, block, portDummies);
            System.out.println("Running dummy port...");
            dummy.start();
            try {
                synchronized(block){
                    System.out.println("Waiting...");
                    block.wait();
                    System.out.println("Block notified.");
                }
            } catch (InterruptedException e) {
                System.out.println("Can't be interrupted!");
                e.printStackTrace();
            }
        }
    }
}

PortDummy（可运行）类：

   package server;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.HashMap;

public class PortDummy extends Thread {

    private Object block;
    private HashMap<String, PortDummy> portDummies;
    private String clientName = null;
    ServerSocket serverSocket;
    BufferedReader socketIn;
    PrintWriter socketOut;

    public PortDummy(ServerSocket serverSocket, Object block, HashMap<String, PortDummy> portDummies){
        this.block = block;
        this.portDummies = portDummies;
        this.serverSocket = serverSocket;
    }

    @Override
    public void run() {
        try {
            System.out.println("Starting dummy port...");
            Socket clientSocket = serverSocket.accept();
            System.out.println("Connection made.");
            synchronized(block){
                System.out.print("Notifying...");
                block.notify();
                System.out.println("...done.");
            }

            socketIn = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
            socketOut = new PrintWriter(clientSocket.getOutputStream(), true);

            String inContent;

            boolean loggedIn = false;
            while((inContent = socketIn.readLine()) != null){   
                socketOut.println("Server Echo: " + inContent);
                if(inContent.startsWith("/exit")){
                    if(loggedIn){
                        portDummies.remove(clientName);
                        System.out.println(clientName + " signed out. Removed from portDummies.");
                    }
                    else{
                        System.out.println("Closing...");
                    }
                }
                else if(inContent.startsWith("/register")){
                    System.out.println("/register accepted");
                    if(!loggedIn){
                        if(registerUser(inContent)){
                            System.out.println("Successfully registered.");
                            socketOut.println(clientName + " successfully registered.");
                            loggedIn = true;
                        }else{
                            socketOut.print("That user already exists.");
                        }
                    }
                    else{
                        socketOut.print("Already logged in.");
                    }
                }
                else if(inContent.startsWith("/tell")){
                    if(!loggedIn){
                        socketOut.println("You need to log in.");
                    }
                    else{
                        String[] parts = inContent.split("\\w");
                        String[] withoutCommand = new String[parts.length-1];
                        for(int i = 1; i<parts.length-1; i++){
                            withoutCommand[i] = parts[i];
                        }
                        String[] messageParts = new String[withoutCommand.length-1];
                        String message = "";
                        for(int j = 1; j<withoutCommand.length-1; j++){
                            message += withoutCommand[j] + " ";
                        }

                        String recipient = withoutCommand[0];
                        sendMessage(recipient, message);
                    }
                }
                else if(inContent.startsWith("/help")){
                    socketOut.print("/help ~~~~~~~ List all commands. \n " +
                            "/register <username> ~~~~~~~ Register a new user with 'username'. \n " +
                            "/tell <username> <message> ~~~~~~~ Send 'username' text 'message'. \n " +
                            "/exit ~~~~~~~ Log out.");
                }
            }

            System.out.println("Shutting down client connections...");
            socketOut.close();
            socketIn.close();
            clientSocket.close();
            serverSocket.close();

        } catch (IOException e) {
            System.out.println("IOException!");
            e.printStackTrace();
        }       
    }

    private boolean registerUser(String text){
        System.out.println("Registering user...");
        String user = text.substring(10);
        if((user != null) && !(portDummies.containsKey(user))){
            portDummies.put(user, this);
            clientName = user;
            System.out.println(user + " registered.");
            return true;
        }
            return false;
    }

    private void sendMessage(String username, String message){
        if(portDummies.containsKey(username)){
            PortDummy recip = portDummies.get(username);
            recip.getSocketOutput().println(clientName + ": " + message);
        }
        else{
            socketOut.write("User " + username + " doesn't exist.");
        }
    }

    public PrintWriter getSocketOutput(){
        return socketOut;
    }
}

客户端类：

package client;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;
import java.util.Scanner;
import java.io.IOException;

public class Client {

    protected String username;

    public static void main(String[] args){
        try{
            Socket serverSocket = new Socket("localhost", 8000);
            BufferedReader socketIn = new BufferedReader(new InputStreamReader(serverSocket.getInputStream()));
            PrintWriter socketOut = new PrintWriter(serverSocket.getOutputStream(), true);

            Scanner keyboardInputScanner = new Scanner(System.in);
            String keyboardInput, serverInput;
            System.out.println("Welcome to Chris Volkernick's Server IM Client! \n" +
                    "Type '/register <username>' to register, '/list' to list connected users," +
                    "\n or '/tell <username> <message>' to send a user a message. '/help' lists these commands. (Type '/exit' to sign out.)");
            while((keyboardInput = keyboardInputScanner.nextLine()) != null){
                System.out.println("Input '" + keyboardInput + "' read on client side.");
                if(keyboardInput.equals("/exit")){
                    socketOut.println("/exit");
                    socketOut.close();
                    socketIn.close();
                    serverSocket.close();
                }else{
                    socketOut.println(keyboardInput);

                    while((serverInput = socketIn.readLine()) != null){
                        System.out.println(serverInput);
                    }
                }           
            }       
            keyboardInputScanner.close();

        }catch(IOException e){
            System.out.println("IOException!");
            e.printStackTrace();
        }       
    }
}

我在 wait() 和/或 notification() 方面做错了什么吗？

编辑：我还尝试将实现 Runnable 更改为扩展Thread，然后将服务器中的 .run() 更改为 .start() ，但这给了我这个错误：

java.net.BindException: Address already in use: JVM_Bind
    at java.net.PlainSocketImpl.socketBind(Native Method)
    at java.net.PlainSocketImpl.bind(PlainSocketImpl.java:365)
    at java.net.ServerSocket.bind(ServerSocket.java:319)
    at java.net.ServerSocket.<init>(ServerSocket.java:185)
    at java.net.ServerSocket.<init>(ServerSocket.java:97)
    at server.PortDummy.run(PortDummy.java:28)

编辑2：它似乎正在按应有的方式工作现在就启动新线程而言。但是，我现在遇到了另一个问题：在任何给定客户端的客户端输入命令后，我无法输入其他命令。第一个命令可以正常工作（减去 /exit；还没有完全弄清楚它应该如何工作），只是之后无法执行任何操作。例如，我可以注册（登录），但之后就什么都没有了。我可以进入客户端的另一个实例并列出所有当前用户（有效），但同样，此后我无法输入其他命令。知道可能发生什么原因导致这种情况吗？

Answer 1

问题是您的子线程正在尝试侦听端口 8000，但父线程已经在这样做。您需要做的是通过接受来自原始套接字的连接，然后将其交给子线程。我不太确定如何在 Java 中执行此操作，但我怀疑这只是......

将其放入您的主线程中：

ServerSocket serverSocket = new ServerSocket(8000);
Socket clientSocket = serverSocket.accept();

然后一旦您得到它，将 clientSocket 传递给您的 Thread< /代码>。

这样，只有一个套接字侦听端口 8000，但您可以让子线程处理每个连接。

Answer 2

使用等待和通知时，请注意通知不会排队，因此如果通知发生在等待发生之前，您将永远不会退出等待。因此，您永远不应该执行裸等待，即应该始终测试某些条件来确定是否应该等待。

sychronized(block) {
   while (!available) {
       block.wait();
   }
}

​

synchronized(block) {
    available = true;
    block.notifyAll();
}

等等

Answer 3

package so_7775790;

import java.io.InputStream;
import java.io.OutputStream;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.logging.Logger;


/**
 * barebones server -- ctl-C to kill it ;)
 */
public class Server implements Runnable {

    final static Logger log = Logger.getLogger(Server.class.getSimpleName());


    public static void main(String[] args) {
        final int port = 8000;
        final String tname = "my-server-thread";
        final Server server = new Server(port);

        try {
            Thread tserver = new Thread(server, tname);
            tserver.start();
            tserver.join();
        } catch (Exception e) {
            log.severe(e.getMessage());
        }
    }


    // -------------------------------------------------
    // server
    // -------------------------------------------------

    final int port;
    public Server(int port) {
        this.port = port;
    }
    public void run() {
        try{
            final ServerSocket srvsocket = new ServerSocket(port);
            log.info(String.format("Server started @ %s\n", srvsocket));

            while(!Thread.currentThread().isInterrupted()){
                Socket newclient = srvsocket.accept();

                // spawn thread and hand off new client to handler
                new Thread(new ClientHandler(newclient)).start();
            }
        }
        catch (Exception e) {
            log.severe(e.getMessage());
        }
        log.info("server stopped");
    }

    // -------------------------------------------------
    // client handler
    // -------------------------------------------------
    static class ClientHandler implements Runnable {
        final Socket socket;
        public ClientHandler(final Socket socket) {
            assert socket != null : "serverthread is null";
            this.socket = socket;
        }
        @SuppressWarnings("unused")
        @Override final
        public void run() {
            log.info(String.format("new client @ %s\n", socket.getRemoteSocketAddress()));
            try {
                final InputStream in = socket.getInputStream();
                final OutputStream out = socket.getOutputStream();

                // NOTE: this is just a stub busy loop!
                for(;;) {
                    /* your protocol impl here .. */
                }

            } catch (Exception e) {
                log.severe(e.getMessage());
            }
            finally {
                try {
                    socket.close();
                }
                catch (Exception e) {
                    log.severe(e.getMessage());
                }
            }
        }
    }
}