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java regex pattern validate ip address


Regular expressions

Regular expressions represents a sequence of symbols and characters expressing a string or pattern to be searched for within a longer piece of text. The abbreviation for regular expression is regex. In programming regular expressions are mainly used to define constraint on strings like password, email validation.

^([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\.([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\.
([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\.([01]?\\d\\d?|2[0-4]\\d|25[0-5])$

This regular expression refers to a pattern with digit from 0 to 255 and follow by a dot “.”, repeat 4 time and ending with no dot “.”

Example

package com.tutorialspointexamples;
 
import java.util.ArrayList;
import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
 
public class RegexTest {
	private static final String PATTERN = 
			"^([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\." +
			"([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\." +
			"([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\." +
			"([01]?\\d\\d?|2[0-4]\\d|25[0-5])$";
	public static void main(String args[]){ 
		List<String> values = new ArrayList<String>();	
		values.add("255.255.255.255"); 
		values.add("127.0.0.1"); 
		values.add("10.10");
		values.add("10.10.10.256");
 
		Pattern pattern = Pattern.compile(PATTERN);
		for (String value : values){
		  Matcher matcher = pattern.matcher(value);
		  if(matcher.matches()){
			  System.out.println("IP "+ value +" is valid");
		  }else{
			  System.out.println("IP "+ value +" is invalid");
		  }		  
		}
	}
}

Output

IP 255.255.255.255 is valid
IP 127.0.0.1 is valid
IP 10.10 is invalid
IP 10.10.10.256 is invalid
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