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Tuesday, August 9, 2016

Validate IP address using Java regex


Step 1. Write a java class with name ValidateIPAddress
Step 2. Write a regex pattern. Learn more about reg expression https://docs.oracle.com/javase/tutorial/essential/regex/
public class ValidateIPAddress {
 
 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)
    {
     //Pass input value has hard coded value or as a input parameter
            String IP = "000.12.12.034";
            System.out.println(IP.matches(PATTERN));
        

    }
}
Step 3. Description about regex

1. ^                   #line start
2. (                #  start of group 
3. [01]?\\d\\d?        # It can be one or two digits. If three digits appear, it must start either 0 or 1
4. |             # or
5. 2[0-4]\\d        # start with 2, follow by 0-4 and end with any digit (2[0-4][0-9])
6. |                   # or
7. 25[0-5]             # start with 2, follow by 5 and ends with 0-5 (25[0-5])
8. )             #  end of group #2
9. \.                  #  follow by a dot "."
10. ....               # repeat with 3 times (3x)
11. $             #end of the line
 
Step 4. Input 1. Hello.IP 2. 000.12.12.034
Step 5. Output 1. false 2.true

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