How to get file extension in Java

By Atul Rai | Last Updated: July 15, 2018 Previous       Next

This tutorial will help you to get the file extension name through the Java programme. Usually file extension name is a string of characters attached to a filename, usually preceded by a full stop and indicating the format of the file.

For example: Sample.txt, FactorialExample.java, Certificate.pdf, etc.

We can get it from a simple core Java programme or by using third party API.

Using Core Java Programme

In this example, we have simply used the String class method lastIndexOf().

package org.websparrow;

public class FileExtension {

	public static void main(String[] args) {

		String fileName = "Hello.java";
		String extension = "";
		String extensionNew = "";
		int index = fileName.lastIndexOf(".");

		if (index > 0) {

			extension = fileName.substring(index + 1); // return ---> "java"
			extensionNew = fileName.substring(index); // return ---> ".java"
		}

		System.out.println("File extension is: " + extension);
		System.out.println("File extension new  is: " + extensionNew);
	}
}

Using Apache Commons IO

Apache Common IO is very popular API for file manipulations. To get the file extension we simply call the getExtension() method of class FilenameUtils.

package org.websparrow;

import org.apache.commons.io.FilenameUtils;

public class FileExtensionNew {
	
	public static void main(String[] args) {

		String extension = "";
		String extension2 = "";
		
		try {
			
			extension = FilenameUtils.getExtension("Hello.java");              // return ---> "java"
			extension2 = FilenameUtils.getExtension("home/java/Test.jar");    // return ---> "jar"
			
		} catch (Exception e) {
			e.printStackTrace();
		}

		System.out.println("File extension is: " + extension);
		System.out.println("File extension  is: " + extension2);
	}
}