Write a java program to find File Extension.

Write a program to read a file name as a string and find out the file extension and return it as output. For example, the file sun.gif has the extension gif.

Input and Output Format

• Input consists of a string that corresponds to a file name.
• The output consists of a string(extension of the input string (filename)).

Refer sample output for formatting specifications

Sample Input 1:

sun.gif

Sample Output 1:

Gif

Program to Find File Extension in Java

Following are the steps to find the extension of the file:

• Input file name from the user as a string.
• Pass the name to extensionString() method.
• Inside the method, create an object of string tokenizer for the specified string and separate the token with ‘.’ (dot) as a delimiter.
• Now, get the token before the ‘.’ (dot) by calling nextToken().
• At last, return it to the user.

import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    String s1 = sc.nextLine();
    System.out.println(extensionString(s1));
  }

  public static String extensionString(String s1) {
    StringTokenizer t = new StringTokenizer(s1, ".");
    t.nextToken();
    String s2 = t.nextToken();
    return s2;
  }

}

Output

Get File Extension using Library

Here, we will use the external library to get the extension of the file. We have a Utility class inside Apache Common IO. Use the following steps to use it:

• You need to create a Maven project using any IDE (We are using Eclipse IDE)
• Next, add the following dependency into the pom.xml file

<!-- https://mvnrepository.com/artifact/commons-io/commons-io -->
<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.11.0</version>
</dependency>

• At last, use the utility class to fetch the extension name of the file and call the getExtension() method.

Program to get extension file in Java using Apache Common IO

package com.demo;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

import org.apache.commons.io.FilenameUtils;

public class Main {

 public static void main(String args[]) throws IOException {
  BufferedReader bf = new BufferedReader(new InputStreamReader(System.in));
  String s1 = bf.readLine();
  System.out.print(FilenameUtils.getExtension(s1));
 }
}

Output

Extract File Extension using Guava Library

Here, we will use another external library to get the extension of the file. We have a Utility class inside Guava Library. Use the following steps to use it:

• You need to create a Maven project using any IDE (We are using Eclipse IDE)
• Next, add the following dependency into the pom.xml file

<!-- https://mvnrepository.com/artifact/com.google.guava/guava -->
<dependency>
    <groupId>com.google.guava</groupId>
    <artifactId>guava</artifactId>
    <version>31.0.1-jre</version>
</dependency>

• At last, use the utility class to fetch the extension name of the file and call the getFileExtension() method.

Program to get the File Extension in Java

package com.IPAddress;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import com.google.common.io.Files;

public class FileExtension {

 public static void main(String args[]) throws IOException {
  BufferedReader bf = new BufferedReader(new InputStreamReader(System.in));
  String s1 = bf.readLine();
  System.out.print(Files.getFileExtension(s1));
 }
}

Output

Thus, in this way, we learned how to find the extension of files in Java.