如何以正确的方式关闭插座？ [英] How can I close the socket in a proper way?

问题描述

这是一个简单的TCP服务器。程序终止后如何关闭套接字？
我使用try / finally并尝试关闭套接字。但是当我退出程序时它不会运行finally块。

This is a simple TCP server. How can i close the socket when the program is terminated? I have using try/finally and try to close the socket. But it doesn't run the finally block when I exit the program.

任何人都可以知道如何以正确的方式关闭套接字？

Anyone can have idea on how to close the socket in a proper way?

try {
        socket = new ServerSocket(port);
        System.out.println("Server is starting on port " + port + " ...");
    }catch (IOException e){
        System.out.println("Error on socket creation!");
    }

    Socket connectionSocket = null;
    try{
        while(true){            
            try{
                connectionSocket = socket.accept();
                Thread t =  new Thread(new ClientConnection(connectionSocket));
                t.start();
            }catch (IOException e) {
                System.out.println("Error on accept socket!");
            }
        }
    }finally{
        this.socket.close();
        System.out.println("The server is shut down!");
    }

推荐答案

创建ServerSocket后，你可以添加 ShutdownHook 在JVM终止时关闭它，如下所示：

After creating your ServerSocket, you could add a ShutdownHook to close it on JVM termination, something like this:

Runtime.getRuntime().addShutdownHook(new Thread(){public void run(){
    try {
        socket.close();
        System.out.println("The server is shut down!");
    } catch (IOException e) { /* failed */ }
}});

调用 ServerSocket #close 将终止阻塞 ServerSocket.accept 调用，导致它抛出SocketException。但请注意，您在while循环中当前对IOException的处理意味着您将重新进入while循环以尝试在已关闭的套接字上接受。 JVM仍将终止，但它有点不整洁。

Invoking ServerSocket#close will terminate the blocking ServerSocket.accept call, causing it to throw a SocketException. However, note that your current handling of IOException in the while loop means you will then re-enter the while loop to attempt accept on a closed socket. The JVM will still terminate, but it's a bit untidy.

如果在Eclipse中终止控制台应用程序（至少在Windows上），则不会运行关闭挂钩。但是如果你在普通控制台中使用CTRL-C Java，它们就会运行。要让它们运行，您需要正常终止JVM，例如SIGINT或SIGTERM而不是SIGKILL（kill -9）。

Shutdown hooks do not run if you terminate a console application in Eclipse (on Windows at least). But they do run if you CTRL-C Java in a normal console. For them to run, you need the JVM to be terminated normally, e.g. SIGINT or SIGTERM rather than SIGKILL (kill -9).

一个可以在Eclipse或控制台中执行的简单程序将证明这一点。

A simple program which you can execute in Eclipse or a console will demonstrate this.

public class Test implements Runnable {

  public static void main(String[] args) throws InterruptedException {
    final Test test = new Test();
    Runtime.getRuntime().addShutdownHook(new Thread(){public void run(){
      test.shutdown();
    }});
    Thread t = new Thread(test);
    t.start();
  }

  public void run() {
    synchronized(this) {
      try {
        System.err.println("running");
        wait();
      } catch (InterruptedException e) {}
    }
  }

  public void shutdown() {
    System.err.println("shutdown");
  }
}

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