Using Regular Expressions to validate a filename in a FileUpload control

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.

(			#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

Example in Java:

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();

	  }
}

[color=blue]Image file that match:[/color]
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”

[color=blue]Image that doesn’t match:[/color]
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 kaiyang
 *
 */
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:
[code="java"]
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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