Introduction

Java is a programming language commonly used for developing applications, especially web applications. One of the tasks that an application may need to perform is to obtain the IP address of the host it is running on. In this article, we will discuss how to obtain the IP address in Java.

Using Java APIs to Obtain Local IP Address

Java provides a set of APIs to access the network information. One of these APIs is the NetworkInterface class which can be used to obtain the local IP address of a system. To get the IP address, first, we need to get the list of available network interfaces using the getNetworkInterfaces() method of the NetworkInterface class. Then we can iterate over the list and get the IP address of each interface using the getInetAddresses() method. The following code snippet demonstrates how to obtain the local IP address in Java:

NetworkInterface networkInterface = NetworkInterface
    .getByName("eth0");

Enumeration inetAddresses =
    networkInterface.getInetAddresses();

while (inetAddresses.hasMoreElements()) {
    InetAddress inetAddress = inetAddresses.nextElement();
    if (!inetAddress.isLinkLocalAddress()
        && !inetAddress.isLoopbackAddress()
        && inetAddress instanceof Inet4Address) {
        System.out.println(inetAddress.getHostAddress());
    }
}

The code above gets the network interface named "eth0" and enumerates over its IP addresses. It then checks if the IP address is not a link-local or loopback address and that it is an IPv4 address, and finally, it prints out the host address of the IP address.

Using Third-party Libraries to Obtain Local IP Address

In addition to the built-in Java APIs, there are also third-party libraries that can be used to obtain the local IP address in a more straightforward way. One of these libraries is Apache Commons Net, which provides a set of classes to access network information. The following code snippet demonstrates how to use the Apache Commons Net library to obtain the local IP address:

String localIpAddress = InetAddress.getLocalHost()
    .getHostAddress();
System.out.println(localIpAddress);

The code above simply gets the local host address using the getLocalHost() method of the InetAddress class and prints it out to the console.

Conclusion

In this article, we have discussed how to obtain the local IP address in Java using both the built-in Java APIs and third-party libraries. Obtaining the IP address is a common task in network programming, and knowing how to obtain it in Java can be useful in various types of applications.