DateRecognizerFilterFactory gives every filter it creates the same java.text.DateFormat, so an analyzer built from it throws NumberFormatException or ArrayIndexOutOfBoundsException when several threads analyse text at the same time

Finding LFV-483Area: analysis / analysis-common miscellaneous filters (DateRecognizerFilterFactory, DateRecognizerFilter)Priority: mediumImpact: crashNovelty: new

Finding page for LFV-483

AI-assisted finding, confirmed by automated checks, not yet triaged by a human Lucene committer. This site files nothing upstream.

What it shows

You build an analyzer with CustomAnalyzer from a whitespace tokenizer and the dateRecognizer filter (datePattern=yyyy-MM-dd, locale=en-US) and analyse text such as '2024-01-15 foo 1999-12-31' from four threads at once, as IndexWriter does with its indexing threads. You expect every thread to get the same date tokens as a single-threaded run, because Analyzer gives each thread its own set of token stream components. Instead some analyses throw NumberFormatException ('multiple points', 'For input string: ""') or ArrayIndexOutOfBoundsException, because DateRecognizerFilterFactory creates one java.text.DateFormat, which is not thread-safe, and create() passes that same instance to the filter of every thread.

The test shows that an analyzer built with DateRecognizerFilterFactory (via CustomAnalyzer) throws when two threads use it at once: every filter the factory creates gets the same java.text.DateFormat, which is not thread-safe.

Expected vs actual

Expected no exception (Analyzer gives each thread its own filter); actual NumberFormatException out of SimpleDateFormat.parse in DateRecognizerFilter.accept (-ea and -da; needs two CPUs running the threads in parallel).

Files

• src/org/apache/lucene/analysis/miscellaneous/TestDateRecognizerFactoryThreads.java (JUnit test)

Run it

• Tested on Lucene main e1faeba08bde (2026-11-02): still reproduces.
• Tested on Lucene main 645d4fe14a20 (2026-10-28): reproduced.
• Recorded outcome of run 1 on Lucene main 645d4fe14a20: 1 test(s) run, 1 failed.
• How to read the outcome: a failing test is the finding reproducing (the failure message states expected against actual).
• Seeds: a rerun with the same seed replays the same random choices. Assertions off (-da -dsa -Dtests.asserts=false) is the production-like setting.

# Lucene checkout at the tested commit, built with: ./gradlew --no-daemon assemble   (JDK 25)
LUCENE=/path/to/lucene; V=12.0.0-SNAPSHOT
CP=$LUCENE/lucene/core/build/libs/lucene-core-$V.jar
CP=$CP:$LUCENE/lucene/codecs/build/libs/lucene-codecs-$V.jar
CP=$CP:$LUCENE/lucene/test-framework/build/libs/lucene-test-framework-$V.jar
CP=$CP:$LUCENE/lucene/analysis/common/build/libs/lucene-analysis-common-$V.jar
CP=$CP:randomizedtesting-runner-2.9.2.jar:junit-4.13.2.jar:hamcrest-3.0.jar   # test-framework dependencies (Maven Central)
CP=$CP:junit-platform-console-standalone-6.1.3.jar   # JUnit Platform console launcher (Maven Central)

javac -d classes -cp "$CP" $(find src -name '*.java')

# run 1: assertions on, seed DEADBEEF
java -ea -esa --add-modules jdk.incubator.vector --enable-native-access=ALL-UNNAMED -Dtests.seed=DEADBEEF \
     -cp "classes:$CP" org.junit.platform.console.ConsoleLauncher \
     execute --select-class org.apache.lucene.analysis.miscellaneous.TestDateRecognizerFactoryThreads

Gradle alternative: copy the test into the matching module's src/test/ tree of the checkout and run ./gradlew -p lucene/<module> test --tests <class> -Ptests.seed=<seed> (add -Ptests.asserts=false for a run without assertions).

Feedback

Open an issue in lucene-ai-bug-hunt. Please do not open issues or pull requests in apache/lucene about this finding unless a Lucene committer agrees it should be filed.

Snapshot of 2026-11-03. AI-assisted; not yet triaged by a human Lucene committer. Feedback: open an issue in lucene-ai-bug-hunt.