How Do I Get My External IP Address Using Java?

How Can I Retrieve the External IP Address in Java?

Understanding the concept of local and external IP addresses is crucial for networking applications. When a computer is connected to a local area network (LAN), it has a local IP address used for internal communication within the network. However, when accessing the internet, the computer requires an external IP address, which is visible to devices outside the network.

IP Address Lookup

The IPAddress class provided in the question is designed to obtain the local IP address of the machine. To retrieve the external IP address, a different approach is needed. One common method involves using web services.

Web Service Integration

Web services such as AWS's checkip API provide a convenient way to determine the external IP address. Here's how to utilize this service in Java:

import java.net.URL;
import java.io.BufferedReader;
import java.io.InputStreamReader;

public class ExternalIPAddress {

    public static void main(String[] args) {
        try {
            URL whatismyip = new URL("http://checkip.amazonaws.com");
            BufferedReader in = new BufferedReader(new InputStreamReader(
                    whatismyip.openStream()));

            String ip = in.readLine(); // Read the external IP address
            System.out.println("Your external IP: " + ip);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

In this code, we make a request to the checkip web service and read the response to obtain the external IP address. This address can then be used in various networking applications where external communication is necessary.

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