Strex

Generate a sorted string list from a regular expression.

Strex is a java library for generating an alphabetically sorted lazy list of all the strings that match a given fixed-length regular expression.

Add to projects

Gradle projects:

dependencies {
    implementation "hu.webarticum.strex:strex:${strexVersion}"
}

Maven projects:

<dependency>
  <groupId>hu.webarticum.strex</groupId>
  <artifactId>strex</artifactId>
  <version>${strexVersion}</version>
</dependency>

Example

Here is a little demonstration of the key features:

Strex identifiers = Strex.compile("PID:\\d{3}\\-[a-f]{5}\\-[xrbc]{3}");
System.out.println(identifiers.size());                       // 497664000 ( = 10^3 × 1 × 6^5 × 1 × 4^3 )
System.out.println(identifiers.get(0));                       // PID:000-aaaaa-bbb
System.out.println(identifiers.get(497663999));               // PID:999-fffff-xxx
System.out.println(identifiers.indexOf("PID:354-fedab-xbb")); // 176650096

Features

Currently, a limited subset of regular expression features is supported:

• simple literals (e. g. a)
• escaped literals (e. g. \t, \.)
• normal character classes (e. g. [a-f\d])
• negated character classes (e. g. [^\da-fA-F])
• predefined character classes (\s, \S, \w, \W, \d, \D)
• dot (.), generates a printable ASCII character
• fixed quantifier (e. g. {3})
• optional ^ and $ anchors
• non-ascii characters (e. g. ű{3}[a-záé])

In the future, it's planned to extend this functionality to support dynamic-length patterns, but this requires a completely new, much more complex engine. This is a low-priority task.

What is this good for?

There are many regex-based random string generators. Strex's main goal is different. It provides the full list of matching strings alphabetically sorted (even if the trivial tree traversal would not give an alphabetical result). This list can be very large, so simply sorting is not an option.

HoloDB uses Strex for generating random strings by a regex. To achieve this, it selects random indices (in an invertible way) and provides the associated strings for these. Because we can execute an efficient search in this virtual list, such table columns can be indexed.