ID, Password regexp pattern

regexp.java

// Id starts with alphabet and alphanumeric characters. Minimum length 4, Maximum length 20.
@Pattern(regexp = "^[a-zA-Z]{1}[a-zA-Z0-9_]{4,20}$")

// Password requires at least number, capital character, non-capital character and special character. Minimum length 8, Maximum length 20.
// ^                 # start-of-string
// (?=.*[0-9])       # a digit must occur at least once
// (?=.*[a-z])       # a lower case letter must occur at least once
// (?=.*[A-Z])       # an upper case letter must occur at least once
// (?=.*[@#$%^&+=])  # a special character must occur at least once
// (?=\S+$)          # no whitespace allowed in the entire string
// .{8,20}           # anything, at least eight places at most 20 though
//$                  # end-of-string
@Pattern(regexp = "((?=.*\\d)(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%]).{8,20})"