多线程套接字通信客户端/服务器

Question

我完成了一个工作正常的客户端/服务器套接字通信程序。 现在我想弄清楚如何做到这一点，以便我可以同时拥有到服务器的多个客户端连接。 我环顾四周，似乎有不止几种不同的方法可以做到这一点。 所以我来这里是为了向你们寻求帮助/建议。

我的服务器：

public class Server {
    private ServerSocket serverSocket = null;
    private Socket clientSocket = null;

    public Server() {
        try {
            serverSocket = new ServerSocket(7003);
        } catch (IOException e) {
            System.err.println("Could not listen on port: 7003");
            System.exit(1);
        }

        try {
            clientSocket = serverSocket.accept();
        } catch (IOException e) {
            System.err.println("Accept failed");
            System.exit(1);
        }
    }

    public void startServer() throws IOException {
        PrintWriter output = new PrintWriter(clientSocket.getOutputStream(), true);
        BufferedReader input = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));

        String inputLine, outputLine;

        outputLine = "Connected to Server";
        output.println(outputLine);

        while ((inputLine = input.readLine()) != null) {
            // This just determines users input and server ruturns output based on that

            outputLine = this.getServerOutput(inputLine);
            output.println(outputLine);

            if (outputLine.equals("Bye"))
                break;
        }

        output.close();
        input.close();
        clientSocket.close();
        serverSocket.close();
    }
}

我需要让我的构造函数创建线程和startServer()还是我的 run 方法？

Answer 1

您应该使用ExecutorService 。 您的客户端请求处理将是Runnable的run()并且在每次接受之后您可以调用ExecutorService.submit(runnableTask)以异步服务客户端。

使用 ExecutorService 的示例。

public class MyServer {

    private static MyServer server; 
    private ServerSocket serverSocket;

    /**
     * This executor service has 10 threads. 
     * So it means your server can process max 10 concurrent requests.
     */
    private ExecutorService executorService = Executors.newFixedThreadPool(10);        

    public static void main(String[] args) throws IOException {
        server = new MyServer();
        server.runServer();
    }

    private void runServer() {        
        int serverPort = 8085;
        try {
            System.out.println("Starting Server");
            serverSocket = new ServerSocket(serverPort); 

            while(true) {
                System.out.println("Waiting for request");
                try {
                    Socket s = serverSocket.accept();
                    System.out.println("Processing request");
                    executorService.submit(new ServiceRequest(s));
                } catch(IOException ioe) {
                    System.out.println("Error accepting connection");
                    ioe.printStackTrace();
                }
            }
        }catch(IOException e) {
            System.out.println("Error starting Server on "+serverPort);
            e.printStackTrace();
        }
    }

    //Call the method when you want to stop your server
    private void stopServer() {
        //Stop the executor service.
        executorService.shutdownNow();
        try {
            //Stop accepting requests.
            serverSocket.close();
        } catch (IOException e) {
            System.out.println("Error in server shutdown");
            e.printStackTrace();
        }
        System.exit(0);
    }

    class ServiceRequest implements Runnable {

        private Socket socket;

        public ServiceRequest(Socket connection) {
            this.socket = connection;
        }

        public void run() {

            //Do your logic here. You have the `socket` available to read/write data.

            //Make sure to close
            try {
                socket.close();
            }catch(IOException ioe) {
                System.out.println("Error closing client connection");
            }
        }        
    }
}

Answer 2

如何使我可以同时与服务器建立多个客户端连接

现在您正在启动您的服务器并立即等待单个客户端在构造函数中连接。

clientSocket = serverSocket.accept();

然后在startServer()方法中处理单个套接字连接。 这意味着不会处理其他客户端。

public void startServer() throws IOException {
    PrintWriter output = new PrintWriter(clientSocket.getOutputStream(), true);
    ...

通常使用这样的服务器模式，您将执行以下操作：

1. 在构造函数中设置您的服务器套接字。
2. 创建一个acceptClients()方法，该方法将循环等待客户端被接受。 这可以分叉一个线程以在其自己的后台线程中接受客户端。
3. 对于每个客户端，要么派生一个线程来处理连接，将线程传递给客户端套接字。 正如@basiljames 所示，最好使用ExecutorService为您管理线程。

这是一些示例代码：

public class Server {
    private ServerSocket serverSocket = null;

    public Server(int portNumber) throws IOException {
        serverSocket = new ServerSocket(portNumber);
    }

    // this could be run in a thread in the background
    public void acceptClients() throws IOException {
        // create an open ended thread-pool
        ExecutorService threadPool = Executors.newCachedThreadPool();
        try {
            while (!Thread.currentThread().isInterrupted()) {
                // wait for a client to connect
                Socket clientSocket = serverSocket.accept();
                // create a new client handler object for that socket,
                // and fork it in a background thread
                threadPool.submit(new ClientHandler(clientSocket));
            }
        } finally {
            // we _have_ to shutdown the thread-pool when we are done
            threadPool.shutdown();
        }
    }

    // if server is running in background, you stop it by killing the socket
    public void stop() throws IOException {
        serverSocket.close();
    }

    // this class handles each client connection
    private static class ClientHandler implements Runnable {
        private final Socket clientSocket;
        public ClientHandler(Socket clientSocket) {
            this.clientSocket = clientSocket;
        }
        public void run() {
            // use the client socket to handle the client connection
            ...
        }
    }
}

建议对几乎所有像这样的Thread实现使用ExecutorService线程池。 但是，如果您出于某种原因坚持使用原始Thread ，则可以在acceptClients()方法中执行以下操作：

    public void acceptClients() throws IOException {
        while (!Thread.currentThread().isInterrupted()) {
            // wait for a client to connect
            Socket clientSocket = serverSocket.accept();
            // fork a background client thread
            new Thread(new ClientHandler(clientSocket)).start();
        }
    }

Answer 3

更改此： public void startServer() throws IOException到此： public void startServer(Socket clientSocket) throws IOException

那么你需要做的就是：

public Server()
{
    try
    {
        serverSocket = new ServerSocket(7003);
    }
    catch (IOException e)
    {
        System.err.println("Could not listen on port: 7003");
        System.exit(1);
    }

    try
    {
        while(true) {
            final Socket socket = serverSocket.accept();
            new Thread(new Runnable() {
                public void run() {
                    try {
                        startServer(socket);
                    } catch(IOException e) {e.printStackTrace();}
                }
            }).start();
        }
    }
    catch(IOException e)
    {
        System.err.println("Accept failed");
        System.exit(1);
    }
}

最后，您可以删除private Socket clientSocket = null;

那应该会让你到达那里。 或者至少非常接近。

Answer 4

private static final int SERVER_PORT = 35706;
private ServerSocket serverSocket;
private final ArrayList<ClientThread> activeClients = new ArrayList<>();

public void startServer() {

    try {
        serverSocket = new ServerSocket(SERVER_PORT);
        
        final ExecutorService clientPool = Executors.newCachedThreadPool();

        while (!serverSocket.isClosed()) {

            try {
                Future<Socket> future = clientPool.submit(() -> {
                       Socket socket = serverSocket.accept();
                       ClientThread clientThread= new ClientThread(socket);
                       return (socket);
                });

                activeClients.add(future.get());
            } catch (IOException e) {
                clientPool.shutdownNow();
                System.out.println(e.getMessage());
            } catch (InterruptedException | ExecutionException e) {
                System.out.println(e.getMessage());
            }
        }

    } catch (IOException e) {
        System.out.println(e.getMessage());
    }
}



public void stopServer() {  

   try {
        serverSocket.close();
        activeClients.forEach(socket -> {
            try {
                socket.close();
            } catch (IOException e) {
                System.out.println(e.getMessage());
            }
        });
            
   } catch (IOException ex) {
        System.out.println(e.getMessage());
   }

}



private static class ClientThread implements Runnable{
    private final Socket socket;

    public ClientThread(Socket socket) throws IOException {
       this.socket = socket;
    }
        
    @Override
    public void run() {
        /* Your implementation */
    }
}