nz.co.gregs:regexi

Regexi

A regular expression library for Java with Named Capture support

Why?

Regular expressions are very powerful but don't scale well.

What does that mean?

The power of the regex language trips up developers very quickly. For instance everyone can search for a number using regex and usually they'll be wrong. The simple and obvious pattern, /[0-9]*/, will incorrectly match ABC0345 but miss 0.89.

A better solution is /(([-+]?\\b([1-9]+\\d\*|0+(?!\\d)))((\\.){1}(\\d+))?){1}/ but 99% developers will recognise that as complete gibberish. What is it doing and why? No one knows, I certainly didn't when I realised I needed to extend an already large expression.

Regexi solves this by implementing all the parts of the regular expression language as part of a chaining class. So instead we would write:

  Regex.startingAnywhere()
  .anyCharacterIn("-+").onceOrNotAtAll()
  .wordBoundary()
  .beginOrGroup()
  .anyCharacterBetween('1', '9').atLeastOnce()
  .digit().zeroOrMore()
  .or().literal('0').oneOrMore().notFollowedBy(Regex.startingAnywhere().digit())
  .endOrGroup()
  .once()
  .toRegex();
  

Or even better

  Regex.startingAnywhere().number().once().toRegex();

Using that in actual Java:

Regex pattern = Regex
    .startingAnywhere()
    .number().once()
    .toRegex();
	
	
final String input = "it should find 0.89 correctly";
if(pattern.matchesWithinString(input)){
    System.out.println("Found it successfully");
    System.out.println("The number we found: "+ pattern.getAllMatches(input).get(0).getEntireMatch());
}

if(!pattern.matchesWithinString("and don't find ABC0345 because it's not a number")){
	    System.out.println("Didn't find it successfully");
}
		
  

Seems nice but I've spotted 5 errors in your regex already.

That's cool, please raise an issue :)

Nothing is ever perfect, so I've kept access to all the parts of the regex language available. You can use PartialRegex to create your own standard patterns and combine them as required.

final PartialRegex oneNumber = Regex.startingAnywhere().number().once();

Anything else I should know about?

Regexi also provides access to the more complicated features of Java's pattern matching easily. In particular

• Named captures are hardly mentioned even in Java's documentation but are easily used and retreived with regexi:

  var regex = Regex.startingFromTheBeginning()
        .beginNamedCapture("interval").literalCaseInsensitive("interval").once().endNamedCapture()
        .space().once()
        .beginNamedCapture("value").numberIncludingScientificNotation().once().endNamedCapture()
        .space().once()
        .beginNamedCapture("unit").word().endNamedCapture()
        .endOfInput()
        .toRegex();
  var captured = regex.getAllMatches(input).get(0).getAllNamedCaptures();
  String value = captured.get("value");
  

• RegexValueFinder streamlines named captures even further to return one value quickly

  RegexValueFinder regex
             = Regex.startingFromTheBeginning()
         .beginNamedCapture("interval").literalCaseInsensitive("interval").once().endNamedCapture()
         .space().once()
         .beginNamedCapture("value").numberIncludingScientificNotation().once().endNamedCapture()
         .space().once()
         .beginNamedCapture("unit").word().endNamedCapture()
         .endOfInput()
         .returnValueFor("value");
        
  String value = regex.getValueFor(input).orElse("");
  

• RegexSplitter chops your input into chunks

  List<String> words = Regex.empty().literal(" ").toSplitter().splitToList(input);
  

• RegexReplacement turns your regular expression into a find/replace using regex:

  String escapeBackslashes = Regex.empty().backslash().replaceWith().backslash().backslash().replaceAll(s);
  

• There are methods for tricky characters like backslash to help you avoid using a regex instruction when you meant a letter

• Similarly the literal(string) method automatically escapes regex instructions to avoid problems

Pronounciation

However works for you is fine, it varies from minute to minute for me.

I do recommend "Rej X I" though.