How to validate image file extension with regular expression

By mkyong | Updated: August 30, 2012

Viewed: 3,051 (+8 pv/w)

Tags: image regex

Image File Extension Regular Expression Pattern

([^\s]+(\.(?i)(jpg|png|gif|bmp))$)

Description

(			#Start of the group #1
 [^\s]+			#  must contains one or more anything (except white space)
       (		#    start of the group #2
         \.		#	follow by a dot "."
         (?i)		#	ignore the case sensive checking for the following characters
             (		#	  start of the group #3
              jpg	#	    contains characters "jpg"
              |		#	    ..or
              png	#	    contains characters "png"
              |		#	    ..or
              gif	#	    contains characters "gif"
              |		#	    ..or
              bmp	#	    contains characters "bmp"
             )		#	  end of the group #3
       )		#     end of the group #2	
  $			#  end of the string
)			#end of the group #1

Whole combination is means, must have 1 or more strings (but not white space), follow by dot “.” and string end in “jpg” or “png” or “gif” or “bmp” , and the file extensive is case-insensitive.

This regular expression pattern is widely use in for different file extensive checking. You can just change the end combination (jpg|png|gif|bmp) to come out different file extension checking that suit your need.

Java Regular Expression Example

package com.mkyong.regex;

import java.util.regex.Matcher;
import java.util.regex.Pattern;
 
public class ImageValidator{
	
   private Pattern pattern;
   private Matcher matcher;
 
   private static final String IMAGE_PATTERN = 
                "([^\\s]+(\\.(?i)(jpg|png|gif|bmp))$)";
	        
   public ImageValidator(){
	  pattern = Pattern.compile(IMAGE_PATTERN);
   }
	  
   /**
   * Validate image with regular expression
   * @param image image for validation
   * @return true valid image, false invalid image
   */
   public boolean validate(final String image){
		  
	  matcher = pattern.matcher(image);
	  return matcher.matches();
	    	    
   }
}

Image file that match:

1. “a.jpg”, “a.gif”,”a.png”, “a.bmp”,
2. “..jpg”, “..gif”,”..png”, “..bmp”,
3. “a.JPG”, “a.GIF”,”a.PNG”, “a.BMP”,
4. “a.JpG”, “a.GiF”,”a.PnG”, “a.BmP”,
5. “jpg.jpg”, “gif.gif”,”png.png”, “bmp.bmp”

Image that doesn’t match:

1. “.jpg”, “.gif”,”.png”,”.bmp” – image file name is required
2. ” .jpg”, ” .gif”,” .png”,” .bmp” – White space is not allow in first character
3. “a.txt”, “a.exe”,”a.”,”a.mp3″ – Only image file extension is allow
3. “jpg”, “gif”,”png”,”bmp” – image file extension is required

Unit Test – ImageValidator

package com.mkyong.regex;

import org.testng.Assert;
import org.testng.annotations.*;
 
/**
 * Image validator Testing
 * @author mkyong
 *
 */
public class ImageValidatorTest {
 
	private ImageValidator imageValidator;
    
	@BeforeClass
        public void initData(){
		imageValidator = new ImageValidator();
        }
    
	@DataProvider
	public Object[][] ValidImageProvider() {
	   return new Object[][]{
    	     {new String[] {
		   "a.jpg", "a.gif","a.png", "a.bmp",
		   "..jpg", "..gif","..png", "..bmp",
		   "a.JPG", "a.GIF","a.PNG", "a.BMP",
		   "a.JpG", "a.GiF","a.PnG", "a.BmP",
		   "jpg.jpg", "gif.gif","png.png", "bmp.bmp"
  	       }
              }
	   };
	}
	
	@DataProvider
	public Object[][] InvalidImageProvider() {
	  return new Object[][]{
	    {new String[] {
		   ".jpg", ".gif",".png",".bmp",
		   " .jpg", " .gif"," .png"," .bmp",
                   "a.txt", "a.exe","a.","a.mp3",
		   "jpg", "gif","png","bmp"
	       }
             }
	   };
	}
	
	@Test(dataProvider = "ValidImageProvider")
	 public void ValidImageTest(String[] Image) {
		
	   for(String temp : Image){
		   boolean valid = imageValidator.validate(temp);
		   System.out.println("Image is valid : " + temp + " , " + valid);
		   Assert.assertEquals(true, valid);
	   }
	   
	}
	
	@Test(dataProvider = "InvalidImageProvider", 
                 dependsOnMethods="ValidImageTest")
	public void InValidImageTest(String[] Image) {
		
	   for(String temp : Image){
		   boolean valid = imageValidator.validate(temp);
		   System.out.println("Image is valid : " + temp + " , " + valid);
		   Assert.assertEquals(false, valid);
	   }
	}	
}

Unit Test – Result

Image is valid : a.jpg , true
Image is valid : a.gif , true
Image is valid : a.png , true
Image is valid : a.bmp , true
Image is valid : ..jpg , true
Image is valid : ..gif , true
Image is valid : ..png , true
Image is valid : ..bmp , true
Image is valid : a.JPG , true
Image is valid : a.GIF , true
Image is valid : a.PNG , true
Image is valid : a.BMP , true
Image is valid : a.JpG , true
Image is valid : a.GiF , true
Image is valid : a.PnG , true
Image is valid : a.BmP , true
Image is valid : jpg.jpg , true
Image is valid : gif.gif , true
Image is valid : png.png , true
Image is valid : bmp.bmp , true
Image is valid : .jpg , false
Image is valid : .gif , false
Image is valid : .png , false
Image is valid : .bmp , false
Image is valid :  .jpg , false
Image is valid :  .gif , false
Image is valid :  .png , false
Image is valid :  .bmp , false
Image is valid : a.txt , false
Image is valid : a.exe , false
Image is valid : a. , false
Image is valid : a.mp3 , false
Image is valid : jpg , false
Image is valid : gif , false
Image is valid : png , false
Image is valid : bmp , false
PASSED: ValidImageTest([Ljava.lang.String;@1d4c61c)
PASSED: InValidImageTest([Ljava.lang.String;@116471f)

===============================================
    com.mkyong.regex.ImageValidatorTest
    Tests run: 2, Failures: 0, Skips: 0
===============================================


===============================================
mkyong
Total tests run: 2, Failures: 0, Skips: 0
===============================================

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