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Java Network API provides a way to find the IP address of local host from Java program using java.net. InetAddressclass. It is rare that you need the IP address of local host in Java program. Most of the time, I use Unix commands to find the IP address of local host. For all practical purposes where program does not require IP address but we need to solve any network problem, use DOS or Windows commands or use Linux commands. Recently one of my friend faced this question in core Java interview, they expect Java developers to have some experience in socket programming, but it is difficult to answer this fact based question until you know or you have done it, which prompted us to write this article.

In this Java tutorial, we will see how to find the IP address of the local host from within a Java program. By the way, it is always a good idea to remember the list of Unix network commands to troubleshoot any network issues related to Java applications in Unix environment.

The IP address of the local host from the Java program

As I said, the in the java.net package InetAddressis used to represent IP addresses in Java. An IP address is a 32-bit or 128-bit unsigned number used by the IP protocol, which is the backbone of many popular protocols such as TCP and UDP.

There are two types of IP addresses, IPv4 and IPv6. An IP address is associated with a host, and the host can be found through the host name resolution process.

Hostname resolution is performed by combining the local machine configuration and network naming services such as DNS (Domain Name System) and NIS (Network Information Service). InetAddressThere is a method to resolve hostname to IP address and vice versa. Here is the complete code example to find IP address from Java program.

import java.net.UnknownHostException;

/**
 * 用于查找本地主机 IP 地址的简单 Java 程序。 这个程序使用
 * InetAddress 从 java.net 包中查找 IP 地址。
 *
 */
public class IPTest {
 
 
    public static void main(String args[]) throws UnknownHostException {
   
        InetAddress addr = InetAddress.getLocalHost();
     
        // 获取本地主机的 IP 地址 - getHostAddress 以文本格式返回 IP 地址
        String ipAddress = addr.getHostAddress();
     
        System.out.println("IP address of localhost from Java Program: " + ipAddress);
     
        //Hostname
        String hostname = addr.getHostName();
        System.out.println("Name of hostname : " + hostname);
     
    }
 
}

The output of the above code is as follows