如何找到可用的端口？ [英] How to find an available port?

问题描述

我想启动一个监听端口的服务器。我可以明确指定端口，它可以工作。但我想以自动方式找到一个端口。在这方面我有两个问题。

I want to start a server which listen to a port. I can specify port explicitly and it works. But I would like to find a port in an automatic way. In this respect I have two questions.

1. 我应该在哪个端口号范围内搜索？ （我使用了端口12345,12346和12347，它很好）。

1. In which range of port numbers should I search for? (I used ports 12345, 12346, and 12347 and it was fine).

如何判断某个端口是否未被其他软件占用？

How can I find out if a given port is not occupied by another software?

推荐答案

如果您不介意使用的端口，请指定端口0到 ServerSocket构造函数它会监听任何空闲端口。

If you don't mind the port used, specify a port of 0 to the ServerSocket constructor and it will listen on any free port.

ServerSocket s = new ServerSocket(0);
System.out.println("listening on port: " + s.getLocalPort());

如果你想使用一组特定的端口，那么最简单的方法就是迭代它们直到一个人工作。这样的事情：

If you want to use a specific set of ports, then the easiest way is probably to iterate through them until one works. Something like this:

public ServerSocket create(int[] ports) throws IOException {
    for (int port : ports) {
        try {
            return new ServerSocket(port);
        } catch (IOException ex) {
            continue; // try next port
        }
    }

    // if the program gets here, no port in the range was found
    throw new IOException("no free port found");
}

可以像这样使用：

try {
    ServerSocket s = create(new int[] { 3843, 4584, 4843 });
    System.out.println("listening on port: " + s.getLocalPort());
} catch (IOException ex) {
    System.err.println("no available ports");
}

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