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Program: How to validate file extensions using regular expression in java?


Description:

The below given example shows how to validate a file extensions using regular expression. The regular expression allows txt, doc, csv, and pdf file extensions only.


Code:
package com.java2novice.regex;

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class MyFileExtenValidation {

private static Pattern fileExtnPtrn = Pattern.compile("([^\\s]+(\\.(?i)(txt|doc|csv|pdf))$)");
	
	public static boolean validateFileExtn(String userName){
		
		Matcher mtch = fileExtnPtrn.matcher(userName);
		if(mtch.matches()){
			return true;
		}
		return false;
	}
	
	public static void main(String a[]){
		System.out.println("Is 'java2novice.pdf' allowed file? "
						+validateFileExtn("java2novice.pdf"));
		System.out.println("Is 'cric.doc' allowed file? "
						+validateFileExtn("cric.doc"));
		System.out.println("Is 'java.gif' allowed file? "
						+validateFileExtn("java.gif"));
		System.out.println("Is 'novice.mp3' allowed file? "
						+validateFileExtn("novice.mp3"));
		System.out.println("Is 'java_2.jpeg' allowed file? "
						+validateFileExtn("java_2.jpeg"));
	}
}

Output:
Is 'java2novice.pdf' allowed file? true
Is 'cric.doc' allowed file? true
Is 'java.gif' allowed file? false
Is 'novice.mp3' allowed file? false
Is 'java_2.jpeg' allowed file? false
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Knowledge Centre
Different types of Access Modifiers
public: Any thing declared as public can be accessed from anywhere.

private: Any thing declared as private can't be seen outside of its class.

protected: Any thing declared as protected can be accessed by classes in the same package and subclasses in the other packages.

default modifier: Can be accessed only to classes in the same package.
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About Author

I'm Nataraja Gootooru, programmer by profession and passionate about technologies. All examples given here are as simple as possible to help beginners. The source code is compiled and tested in my dev environment.

If you come across any mistakes or bugs, please email me to [email protected].

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Reference: Java™ Platform Standard Ed. 7 - API Specification | Java™ Platform Standard Ed. 8 - API Specification | Java is registered trademark of Oracle.
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