java 获取本机ip和外网 ip

在Java中获取本机IP地址（无论是内网还是公网IP）通常有两种方式：

1. **通过网络套接字（Socket）获取**：

import java.net.InetAddress;
import java.net.UnknownHostException;

public class IPFinder {
    public static void main(String[] args) {
        try {
            // 获取本地主机名
            InetAddress localAddress = InetAddress.getLocalHost();
            String ipAddress = localAddress.getHostAddress();

            System.out.println("Local IP: " + ipAddress);

            // 如果需要获取公网IP，有时会通过防火墙设置代理访问，这里需要连接到外部服务器并尝试读取响应头的"X-Forwarded-For"
            // 但这不是标准做法，因为这依赖于网络环境配置，并非所有场景都能保证准确。下面示例仅供参考：
            URL url = new URL("https://api.ipify.org");
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            connection.setRequestMethod("GET");
            if (connection.getResponseCode() == 200) {
                String remoteIp = connection.getHeaderField("X-Forwarded-For");
                if (remoteIp != null && !remoteIp.isEmpty()) {
                    System.out.println("Public IP (via proxy): " + remoteIp);
                } else {
                    System.out.println("Public IP: " + connection.getRemoteSocketAddress());
                }
            } else {
                System.out.println("Failed to get public IP.");
            }

        } catch (UnknownHostException e) {
            System.err.println("Failed to determine local IP address.");
            e.printStackTrace();
        } catch (IOException e) {
            System.err.println("Error while fetching public IP.");
            e.printStackTrace();
        }
    }
}

注意：上述公网IP获取方法仅适用于某些环境，并不是所有网络环境下都能得到正确的结果。