How Can a Java Regexp Effectively Validate Passwords Against a Specific Policy?

Password Validation in Java with Improved Regexp

In a Java application, password validation requirements can be enforced using regular expressions (regex). One such expression is designed to ensure compliance with the following policy:

• At least 8 characters
• Contains at least one digit
• Contains both a lower and upper alpha character
• Contains a special character (@#%$^& =)
• Excludes whitespace characters (space, tab, etc.)

The initial regexp created was:

^.*(?=.{8,})(?=..*[0-9])(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$

However, it lacked the ability to check for whitespace characters. To address this, the modified regexp is:

^(?=.*[0-9])(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=])(?=\S+$).{8,}$

Explanation:

• ^: Start of string
• (?=.*[0-9]): At least one digit
• (?=.*[a-z]): At least one lowercase letter
• (?=.*[A-Z]): At least one uppercase letter
• (?=.*[@#$%^& =]): At least one special character (@#%$^& =)
• (?=S $): No whitespace characters
• .: Any character
• {8,}: Minimum length of 8 characters
• $: End of string

This improved regexp ensures adherence to all the specified password policy requirements, enhancing password security in the Java application.

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