google/re2j

Health v2 · maintenance only

Flags: no_license

Adoption not part of the score

1255 stars · 162 forks observed · 2026-08-28

What it is AI-extracted, prompt v1, taxonomy v1, 2026-08-30, confidence not recorded

RE2/J is a pure Java port of Google's RE2 regular expression engine that guarantees linear-time matching using a nondeterministic finite automaton. It protects applications from catastrophic backtracking (ReDoS) when evaluating regex patterns, especially those from untrusted sources.

Use cases

• prevent regex denial of service from user-supplied patterns
• match regular expressions in linear time on large inputs
• replace java.util.regex for patterns with heavy alternation
• safely evaluate untrusted regex patterns in a web application
• avoid exponential backtracking in Java regex matching

When to choose

• your patterns have deep alternation and java.util.regex may backtrack exponentially
• you accept regex patterns from untrusted users and need ReDoS protection
• you need predictable worst-case matching time on large inputs

When to avoid

• you rely on backreferences or PCRE-specific features
• you need a drop-in java.util.regex replacement with full API parity
• you use flags like CANON_EQ, COMMENTS, or UNICODE_CASE

Facets

library · maturity active

parser security parsers security developer-tools jvm regex re2 linear-time regex-dos pure-java

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