[JAVA] Regular expression for password

How to validate passwords using regular expressions! It took me a whole day to understand that For reference of similar people. .. ..

Required specifications

• Enter the password in 8 to 48 characters using all of the following. ・ Lowercase half-width alphabet ・ Uppercase half-width alphabet ・ Half-width numbers ・ Symbol (Available symbol! "# $% &'() * +,-./ :; <=>? @ [] ^ _` {|} ~)

^(?=.*[a-z])(?=.*[A-Z])(?=.*[0-9])(?=.*[!-/:-@[-`{-~])[!-~]{8,48}$

Java sample code

RegexPassword.java

package sample;

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

public class RegexPassword {
	public static void main(String[] args) {
		Pattern p = Pattern.compile("^$|^(?=.*[a-z])(?=.*[A-Z])(?=.*[0-9])(?=.*[!-/:-@\\[-`{-~])[!-~]*");
		Matcher m = p.matcher("aA1!\"#$%&'()*+,-./:;<=>?@[\\]^_`{|}~");
		Boolean result = m.matches();

		System.out.println("result:" + result);
	}
}

reference

If you know the basic premise of regular expressions If you know the basic premise of regular expressions 2

Easy to read ahead and look back

ASCII character code table is easy to see

For those who do not understand the need for . * Of (? =. * [A-z])

To use regular expressions in Java

Miscellaneous notes

Premise

Language: Java8

Main subject

About regular expressions for passwords First to understand positive look-ahead I wrote and executed the following code to check the operation I was worried about false when it should return true.

package sample;

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

public class RegexWord {
	public static void main(String[] args) {
		Pattern p = Pattern.compile("^(?=.*[a-z])");
		Matcher m = p.matcher("abc");
		Boolean result = m.matches();

		System.out.println("result:" + result);
	}
}

In conclusion, I had to rewrite the line Pattern p = ~ as follows: Pattern p = Pattern.compile("^(?=.*[a-z]).*");