套接字:使用Java发现端口可用性

Question

如何使用Java以编程方式确定给定计算机中端口的可用性？

即给定一个端口号,确定它是否已被使用？

Answer 1

这是实现从Apache来骆驼项目:

/**
 * Checks to see if a specific port is available.
 *
 * @param port the port to check for availability
 */
public static boolean available(int port) {
    if (port < MIN_PORT_NUMBER || port > MAX_PORT_NUMBER) {
        throw new IllegalArgumentException("Invalid start port: " + port);
    }

    ServerSocket ss = null;
    DatagramSocket ds = null;
    try {
        ss = new ServerSocket(port);
        ss.setReuseAddress(true);
        ds = new DatagramSocket(port);
        ds.setReuseAddress(true);
        return true;
    } catch (IOException e) {
    } finally {
        if (ds != null) {
            ds.close();
        }

        if (ss != null) {
            try {
                ss.close();
            } catch (IOException e) {
                /* should not be thrown */
            }
        }
    }

    return false;
}

他们还检查DatagramSocket以检查端口是否可用于UDP和TCP.

希望这可以帮助.

Answer 2

对于Java 7,您可以使用try-with-resource来获得更紧凑的代码:

private static boolean available(int port) {
    try (Socket ignored = new Socket("localhost", port)) {
        return false;
    } catch (IOException ignored) {
        return true;
    }
}

Answer 3

从Java 7开始,David Santamaria的答案似乎不再可靠.但是,看起来您仍然可以可靠地使用Socket来测试连接.

private static boolean available(int port) {
    System.out.println("--------------Testing port " + port);
    Socket s = null;
    try {
        s = new Socket("localhost", port);

        // If the code makes it this far without an exception it means
        // something is using the port and has responded.
        System.out.println("--------------Port " + port + " is not available");
        return false;
    } catch (IOException e) {
        System.out.println("--------------Port " + port + " is available");
        return true;
    } finally {
        if( s != null){
            try {
                s.close();
            } catch (IOException e) {
                throw new RuntimeException("You should handle this error." , e);
            }
        }
    }
}

Answer 4

如果您不太关心性能,可以尝试使用ServerSocket类在端口上进行侦听.如果它抛出一个异常,它就被使用了.

public static boolean isAvailable(int portNr) {
  boolean portFree;
  try (var ignored = new ServerSocket(portNr)) {
      portFree = true;
  } catch (IOException e) {
      portFree = false;
  }
  return portFree;
}

编辑:如果你要做的就是选择一个免费端口,那么new ServerSocket(0)你会找到一个.

Answer 5

以下解决方案的灵感来自Spring核心的SocketUtils实现(Apache许可证).

与使用Socket(...)它的其他解决方案相比,它非常快(在不到一秒的时间内测试1000个TCP端口):

public static boolean isTcpPortAvailable(int port) {
    try (ServerSocket serverSocket = new ServerSocket()) {
        // setReuseAddress(false) is required only on OSX, 
        // otherwise the code will not work correctly on that platform          
        serverSocket.setReuseAddress(false);
        serverSocket.bind(new InetSocketAddress(InetAddress.getByName("localhost"), port), 1);
        return true;
    } catch (Exception ex) {
        return false;
    }
}       

Answer 6

David Santamaria 指出的答案的清理：

/**
 * Check to see if a port is available.
 *
 * @param port
 *            the port to check for availability.
 */
public static boolean isPortAvailable(int port) {
    try (var ss = new ServerSocket(port); var ds = new DatagramSocket(port)) {
        return true;
    } catch (IOException e) {
        return false;
    }
}

这仍然受到 user207421 在 David Santamaria 的答案的评论中指出的竞争条件的影响（此方法关闭 and 返回后，某些东西可能会抢占端口ServerSocket）DatagramSocket。