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

如何使用Java确定哪个网络接口连接到Internet？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();

在Eclipse中，这正是我想要的，192.168.1.105。但是，如果我将其打包到jar文件并运行该程序，则代码返回169.254.234.50。看看这个，我发现这是我机器上的VMware虚拟以太网适配器接口的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，但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?

接口比较

界面[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接口，其中site local = true且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

在我的笔记本电脑上（运行Windows 7，安装了Virtual Box及其网络接口），以下代码打印出我的无线网络名称面对我的本地地址。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者的地址。

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\n", interface_, address);

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

_{（我已更新我的答案 isReachable（...）基于 Mocker Tim的回答。）}

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

有一点需要注意。 socket.bind（...）如果我试图连续运行我的代码太快，就像连接isn那样，地址和端口已经被使用了t足够快地清理干净。 8080 应该是随机端口。

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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