This is simple example to demonstrate the use of InetAddress.getLocalHost() API to retrieve the IP Address details of your local system or where ever the Java program is executed. If you write a server applications, this can be used for getting the server’s IP Address. Lets look at the example code to display the IP Address of your system.

IpAddressExample.java

[code lang=”java”]
package javabeat.net.core;

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

public class IpAddressExample {
public static void main(String[] args) {
InetAddress ipAddress = null;
try{
ipAddress=InetAddress.getLocalHost();
}catch (UnknownHostException exception){
exception.printStackTrace();
}
System.out.println("IP Address : "+ipAddress.getHostAddress());
}
}
[/code]

It is very often required to test the internet connection for performing some operations. If there is no internet connection established, then alternative logic will be executed. Java provides useful classes in java.net package for connecting to the internet. Here I written a very simple example to test if your system is connected to internet.

If you look at the below example, I have created URL object for connecting to www.google.com . It always returns the response code 200 if there is internet connection available. Of no internet connection, it would throw and exception.

InternetConnectionExample.ajav

[code lang=”java”]
package javabeat.net.core;

import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.UnknownHostException;

public class InternetConnectionExample {
public static void main(String[] args) throws UnknownHostException,
IOException {
try {
try {
URL url = new URL("http://www.google.com");
System.out.println(url.getHost());
HttpURLConnection con = (HttpURLConnection) url
.openConnection();
con.connect();
if (con.getResponseCode() == 200){
System.out.println("Connection established!!");
}
} catch (Exception exception) {
System.out.println("No Connection");
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
[/code]

It if often required to get the details of the network connection in your desktop. It will be useful if you could get the details of all the connected network details for the future operations. Java has set of classes in the java.net package which is useful for the Java network programming. In this example I have used NetworkInterface class to get the list of networks connected to the system. It doesn’t provide the network is internet or intranet, but you will be able to use the details to get an idea about the network connection.

Lets look at the example.

NetworkConnectionExample.java

[code lang=”java”]
package javabeat.net.core;

import java.io.IOException;
import java.net.InterfaceAddress;
import java.net.NetworkInterface;
import java.net.UnknownHostException;
import java.util.Enumeration;

public class NetworkConnectionExample {
public static void main(String[] args) throws UnknownHostException, IOException{
Enumeration<NetworkInterface> interfaces = NetworkInterface.getNetworkInterfaces();
while (interfaces.hasMoreElements()) {
NetworkInterface networkInterface = interfaces.nextElement();
System.out.println("Network Interface Name : [" + networkInterface.getDisplayName() + "]");
System.out.println("Is It connected? : [" + networkInterface.isUp() + "]");
for (InterfaceAddress i : networkInterface.getInterfaceAddresses()){
System.out.println("Host Name : "+i.getAddress().getCanonicalHostName());
System.out.println("Host Address : "+i.getAddress().getHostAddress());
}
System.out.println("———————-");
}
}
}
[/code]

Output…

[code]
Network Interface Name : [eth1]
Is It connected? : [true]
Host Name : fe80:0:0:0:2e0:4cff:fe00:2071%3
Host Address : fe80:0:0:0:2e0:4cff:fe00:2071%3
Host Name : krishna-desktop.local
Host Address : 192.168.0.101
———————-
Network Interface Name : [lo]
Is It connected? : [true]
Host Name : ip6-localhost
Host Address : 0:0:0:0:0:0:0:1%1
Host Name : localhost
Host Address : 127.0.0.1
———————-
[/code]