Java Regex match IP address

Posted 2020-08-04 每天更强一点...

Reference:

[1] https://www.mkyong.com/regular-expressions/how-to-validate-ip-address-with-regular-expression/

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

public class IPAddressValidator{

    private Pattern pattern;
    private Matcher matcher;

    private static final String IPADDRESS_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 IPAddressValidator(){
	  pattern = Pattern.compile(IPADDRESS_PATTERN);
    }

   /**
    * Validate ip address with regular expression
    * @param ip ip address for validation
    * @return true valid ip address, false invalid ip address
    */
    public boolean validate(final String ip){
	  matcher = pattern.matcher(ip);
	  return matcher.matches();
    }
}

Description

^		#start of the line
 (		#  start of group #1
   [01]?\\d\\d? #    Can be one or two digits. If three digits appear, it must start either 0 or 1
		#    e.g ([0-9], [0-9][0-9],[0-1][0-9][0-9])
    |		#    ...or
   2[0-4]\\d	#    start with 2, follow by 0-4 and end with any digit (2[0-4][0-9])
    |           #    ...or
   25[0-5]      #    start with 2, follow by 5 and ends with 0-5 (25[0-5])
 )		#  end of group #2
  \.            #  follow by a dot "."
....            # repeat with 3 times (3x)
$		#end of the line

Whole combination means, digit from 0 to 255 and follow by a dot “.”, repeat 4 time and ending with no dot “.” Valid IP address format is “0-255.0-255.0-255.0-255”