Library to generate text from a regular expression in Java

Question

Yup, you read that right. I need a library that is capable of generating random text from a regular expression. So the text should be random, but be matched by the regular expression. It seems it doesn't exist, but I could be wrong.

Just a an example: that library would be capable of taking '[ab]*c' as input, and generate samples such as:

abc
abbbc
bac

etc.

Update: I created something myself: Xeger. Check out http://code.google.com/p/xeger/.

Answer 1

Same question here: http://stackoverflow.com/questions/274011/random-text-generator-based-on-regex

I haven't tried it. Good question!

Answer 2

I am not aware of such a library. If you're interested in writing one yourself, then these are probably the steps you'll need to take:

1. Write a parser for regular expressions (you may want to start out with a restricted class of regexes).

2. Use the result to construct an NFA.

3. (Optional) Convert the NFA to a DFA.

4. Randomly traverse the resulting automaton from the start state to any accepting state, while storing the characters outputted by every transition.

The result is a word which is accepted by the original regex. For more, see e.g. Converting a Regular Expression into a Deterministic Finite Automaton.

Answer 3

Here's a few implementations of such a beast, but none of them in Java (and all but the closed-source Microsoft one very limited in their regexp feature support).

Answer 4

I just created a library for doing this a minute ago. It's hosted here: http://code.google.com/p/xeger/. Carefully read the instructions before using it. (Especially the one referring to downloading another required library.) ;-)

This is the way you use it:

String regex = "[ab]{4,6}c";
Xeger generator = new Xeger(regex);
String result = generator.generate();
assert result.matches(regex);

Answer 5

Here is a Python implementation of a module like that: http://www.mail-archive.com/[email protected]/msg125198.html It should be portable to Java.