Java套接字绑定(bind)两次无异常

Question

当我的应用程序启动时，它绑定(bind)在给定端口上:

public boolean checkIsAlreadyStart() {
    try {
        final ServerSocket server = new ServerSocket();
        server.setReuseAddress(false);
        server.bind(new InetSocketAddress("127.0.0.1",APPLICATION_PORT ));
        if (server.isBound()){
            logger.debug("binding to port: {}", APPLICATION_PORT);
            return false;
        }
        return true;
    } catch (IOException e) {
        logger.error("cannot bind to port", e);
        return true;
    }
}

但是，当我同时运行应用程序的两个实例时，第二个实例仍然可以运行该方法而不会出现 IOException。我必须调用accept()方法吗？

Answer 1

无法重现:

10/04/2013 3:55:34 PM S checkIsAlreadyStart
INFO: Bound to port: 9,999
10/04/2013 3:55:34 PM S checkIsAlreadyStart
SEVERE: cannot bind to port
java.net.BindException: Address already in use: JVM_Bind
    at java.net.PlainSocketImpl.socketBind(Native Method)
    at java.net.PlainSocketImpl.bind(PlainSocketImpl.java:383)
    at java.net.ServerSocket.bind(ServerSocket.java:328)
    at java.net.ServerSocket.bind(ServerSocket.java:286)
    at S.checkIsAlreadyStart(S.java:33)
    at S.main(S.java:63)

然而，由于server是一个局部变量，它可能允许对ServerSocket进行垃圾收集，这将关闭它。如果您的目的是保持端口打开，您应该将 server 设置为实例变量。