如何在 Java 中确定 Internet 网络接口 [英] How to Determine Internet Network Interface in Java

问题描述

您如何确定使用 Java 连接到 Internet 的网络接口?例如，我运行

How do you determine which network interface is connected to the internet using Java? For example, I run

InetAddress.getLocalHost().getHostAddress();

并且在 Eclipse 中，它返回的正是我想要的，192.168.1.105.但是，如果我把它打包成一个jar文件并运行程序，代码返回169.254.234.50.查看这个，我发现这是我机器上一个 VMware Virtual Ethernet Adapter 接口的 IP 地址.

and within Eclipse this returns exactly what I intend, 192.168.1.105. However, if I package this into a jar file and run the program, the code returns 169.254.234.50. Looking into this, I found this is the IP address of a VMware Virtual Ethernet Adapter interface on my machine.

有没有办法确定连接到互联网的接口，同时保持我的代码的可移植性?

Is there any way to determine the interface connected to the internet, yet at the same time maintain portability for my code?

界面对比

接口 [net4]

display name  : Intel(R) Centrino(R) Ultimate-N 6300 AGN
MTU           : 1500
loopback      : false
point to point: false
up            : true
virtual       : false
multicast     : true
HW address    : 00 24 D7 2C 5F 70 
INET address (IPv4): 192.168.1.105
  host name           : MyComputer
  canonical host name : MyComputer
  loopback            : false
  site local          : true
  any local           : false
  link local          : false
  multicast           : false
  reachable           : true

接口 [eth5]

display name  : VMware Virtual Ethernet Adapter for VMnet1
MTU           : 1500
loopback      : false
point to point: false
up            : true
virtual       : false
multicast     : true
HW address    : 00 50 56 C0 00 01 
INET address (IPv4): 169.254.234.50
  host name           : MyComputer
  canonical host name : MyComputer
  loopback            : false
  site local          : false
  any local           : false
  link local          : true
  multicast           : false
  reachable           : true

还有第三个 VMware 界面，site local=true 和 link local=false，因此这些字段也没有任何帮助.

There's a third VMware interface with site local=true and link local=false, so those fields aren't any help either.

推荐答案

在我的笔记本电脑(运行 Windows 7，安装了 Virtual Box 和它的网络接口)上，以下代码打印出我的无线接口的名称以及我的本地地址.它在一天结束时使用蛮力方法，但只会尝试并实际连接到被认为是最佳候选地址的地址.

On my laptop (running Windows 7, with Virtual Box and it's network interface installed) the following code prints out the name of my wireless interface along with my local address. It uses a brute force approach at the end of the day, but will only try and actually connect to addresses that are considered to be the best candidates.

// iterate over the network interfaces known to java
Enumeration<NetworkInterface> interfaces = NetworkInterface.getNetworkInterfaces();
OUTER : for (NetworkInterface interface_ : Collections.list(interfaces)) {
  // we shouldn't care about loopback addresses
  if (interface_.isLoopback())
    continue;

  // if you don't expect the interface to be up you can skip this
  // though it would question the usability of the rest of the code
  if (!interface_.isUp())
    continue;

  // iterate over the addresses associated with the interface
  Enumeration<InetAddress> addresses = interface_.getInetAddresses();
  for (InetAddress address : Collections.list(addresses)) {
    // look only for ipv4 addresses
    if (address instanceof Inet6Address)
      continue;

    // use a timeout big enough for your needs
    if (!address.isReachable(3000))
      continue;

    // java 7's try-with-resources statement, so that
    // we close the socket immediately after use
    try (SocketChannel socket = SocketChannel.open()) {
      // again, use a big enough timeout
      socket.socket().setSoTimeout(3000);

      // bind the socket to your local interface
      socket.bind(new InetSocketAddress(address, 8080));

      // try to connect to *somewhere*
      socket.connect(new InetSocketAddress("google.com", 80));
    } catch (IOException ex) {
      ex.printStackTrace();
      continue;
    }

    System.out.format("ni: %s, ia: %s
", interface_, address);

    // stops at the first *working* solution
    break OUTER;
  }
}

_{(我根据 Mocker 用 isReachable(...) 更新了我的答案蒂姆的回答.)}

_{(I've updated my answer with isReachable(...) based on Mocker Tim's answer.)}

需要注意的一件事.socket.bind(...) 如果我试图连续运行我的代码太快，比如连接没有足够快地清理干净，那么我会咆哮说地址和端口已经在使用中.8080 应该是随机端口吧.

One thing to watch out for. socket.bind(...) would bark at me that the address and port is already in use if I tried to run my code too fast in succession like the connection isn't cleaned up fast enough. 8080 should be a random port maybe.

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