ninjayoto / readable-regex

Java library for creating readable regular expressions

Readable Regex

This library provides a way to make complex regular expressions in Java code more readable.

The best way to explain what it does to show some examples:

 // Matches a single digit
    RegExBuilder.build(anyDigit()); // "[0-9]"

 // Matches exactly 2 digits
    RegExBuilder.build(exactly(2).of(anyDigit())); // "[0-9]{2}"

 // Matches between 2 and 4 letters
    RegExBuilder.build(between(2,4).of(anyLetter())); // "[a-zA-Z]{2,4}"

Characters that have special meaning within a regular expression are escaped automatically:

 // Matches one or more occurrences of the text 'Ho?'
    RegExBuilder.build(oneOrMore().of("Ho?")); // "(Ho\?)+"
    
 // Matches anything except an opening or closing square bracket, or a backslash
    RegExBuilder.build(
        anyCharacterExcept(
            characters('[', ']','\\')
        )
    ); // "[^[\\]\\\\]"

Readability is greatly improved for more complex expressions:

 // More or less validates the format of an email address
 // [_\\-A-Za-z0-9]+(\\.[_\\-A-Za-z0-9]+)*@[A-Za-z0-9]+(\\.[A-Za-z0-9]+)*\\.[a-zA-Z]{2,}
    RegExBuilder.build(
        oneOrMore().of(
            anyOneOf(
                characters('_','-'), range('A','Z'), range('a','z'), range('0','9')
            )
        ),
        zeroOrMore().of(
            text("."),
            oneOrMore().of(
                anyOneOf(
                    characters('_','-'), range('A','Z'), range('a','z'), range('0','9')
                )
            )
        ),
        text("@"),
        oneOrMore().of(
            anyOneOf(
                range('A','Z'), range('a','z'), range('0','9')
            )
        ),
        zeroOrMore().of(
            text("."),
            oneOrMore().of(
                anyOneOf(
                    range('A','Z'), range('a','z'), range('0','9')
                )
            )
        ),
        text("."),
        atLeast(2).of(
            anyLetter()
        )
    );

All classes in the library are immutable, and therefore instances are re-usable and thread-safe.