java - 使用套接字和线程时出现 EOFException/SocketException

Question

这个套接字应用程序工作得很好，直到我添加对服务器的多个客户端连接的支持。然后我从客户端收到 EOFException，并从服务器收到 SocketException: Socket closeed。

服务器.java:

public class Server {

    static final int PORT = 8005;
    static final int QUEUE = 50;

    public Server() {
        while (true) {
            try (ServerSocket serverSocket = new ServerSocket(PORT, QUEUE);
                 Socket socket = serverSocket.accept();
                 DataInputStream input = new DataInputStream(socket.getInputStream());
                 DataOutputStream output = new DataOutputStream(socket.getOutputStream())) {

                Thread thread = new Thread(new Runnable() {
                    @Override
                    public void run() {
                        try {
                            output.writeUTF("Hey, this is the server!");
                            output.flush();
                            System.out.println(input.readUTF());
                        } catch (IOException e) {
                            System.out.println();
                            e.printStackTrace();
                        }
                    }
                });
                thread.start();

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

    public static void main(String[] args) {
        new Server();
    }

}

客户端.java:

public class Client {

    static final String HOST = "localhost";
    static final int PORT = 8005;

    public Client() {
        try (Socket socket = new Socket(HOST, PORT);
             DataInputStream input = new DataInputStream(socket.getInputStream());
             DataOutputStream output = new DataOutputStream(socket.getOutputStream())
        ) {
            System.out.println(input.readUTF());
            output.writeUTF("Hey, this is the client!");
            output.flush();
        } catch (IOException e) {
            System.out.println(e.getMessage());
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        new Client();
    }

}

Answer 1

这里有几个问题:

1. 您正在为每次循环创建一个新的ServerSocket。对于多客户端服务器，您应该打开一个 ServerSocket 并为每个连接的客户端调用 accept()。
2. 一旦 try block 退出，Try-with-resources 就会关闭它提供的所有资源。您正在创建一个使用 output 但独立于 try block 执行的 Thread，因此执行流程离开 try 在thread 完成执行之前阻塞，导致socket(和output)在线程能够使用它们之前被关闭。这是其中一种情况，您的资源需要在 try block 的范围之外使用(在您创建的使用它们的线程中)，因此 try-with-resources 无法完成您的所有操作为您处理资源。

我会将您的服务器代码重新排列为:

public class Server {

    static final int PORT = 8005;
    static final int QUEUE = 50;

    public Server() {
        // create serverSocket once for all connections
        try (ServerSocket serverSocket = new ServerSocket(PORT, QUEUE)) {
            while (true) {
                // accept a client connection, not in a try-with-resources so this will have to be explicitly closed
                final Socket socket = serverSocket.accept();

                Thread thread = new Thread(new Runnable() {
                    @Override
                    public void run() {
                        // limit scope of input/output to where they're actually used
                        try (DataInputStream input = new DataInputStream(socket.getInputStream());
                                DataOutputStream output = new DataOutputStream(socket.getOutputStream())) {
                            output.writeUTF("Hey, this is the server!");
                            output.flush();
                            System.out.println(input.readUTF());
                        } catch (IOException e) {
                            System.out.println();
                            e.printStackTrace();
                        }

                        // implicitly close socket when done with it
                        try {
                            socket.close();
                        } catch (IOException e) {
                            System.out.println();
                            e.printStackTrace();
                        }
                    }
                });
                thread.start();
            }
        } catch (IOException e) {
            System.out.println(e.getMessage());
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        new Server();
    }
}

代码有一些注释来解释一些 Action 。另请注意，socket.close() 调用位于其自己的 try-catch block 中，以确保即使 I/O 流引发异常也能调用它。它可以等效地(或者现在我想起来可能更正确)被放置在 I/O 流 try-catch block 上的 finally block 中。