Maintenance: SimpleQueryRewriter - Improve null safety and add comprehensive tests

[claude]

Summary

Inspected and improved SimpleQueryRewriter - a fallback implementation for query rewriting when AI services are unavailable.

Issues Found

1. Inconsistent null handling:

   • rewrite() returned "" for null input
   • expandForKeywords() returned the original null value
   • This inconsistency could cause NPE in calling code

2. Missing blank string checks:

   • Only checked for null but not whitespace-only strings
   • Could return normalized whitespace as result

3. Poor documentation:

   • Informal Korean comments instead of proper Javadoc
   • No documentation of null handling behavior
   • Missing method-level documentation

4. Code clarity:

   • Variable naming could be clearer (s -> normalized)

5. No test coverage:

   • No unit tests to verify behavior
   • Edge cases not documented or tested

Changes Made

SimpleQueryRewriter.java:

• Added consistent isBlank() checks to both methods
• Both methods now return empty string for null/blank input
• Replaced Korean comments with proper English Javadoc
• Improved variable naming for clarity
• Added comprehensive method documentation

SimpleQueryRewriterTest.java (new):

• Created comprehensive unit tests (16 test cases)
• Tests null, empty, and blank string handling
• Tests normalization: lowercase, space collapsing, trimming
• Tests Korean text and special character handling
• Tests both rewrite() and expandForKeywords() methods
• Follows codebase testing conventions (@UnitTest, DisplayName)

Why These Changes Improve the Code

1. Safety: Consistent null/blank handling prevents NPEs and unexpected behavior
2. Maintainability: Proper Javadoc helps future developers understand behavior
3. Quality: Comprehensive tests document expected behavior and prevent regressions
4. Consistency: Matches patterns used in other "noop" implementations (NoopReranker, etc.)
5. Clarity: Better variable names and documentation make code more readable

All tests pass ✅

🤖 Generated with Claude Code

[claude]

PR Review: SimpleQueryRewriter - Improvements and Feedback

Overall Assessment

Rating: ✅ Approve with Minor Suggestions

This is a solid maintenance PR that addresses real issues in the SimpleQueryRewriter class. The changes improve null safety, documentation, and add comprehensive test coverage. The implementation is clean and follows existing codebase patterns.

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Code Quality & Best Practices

✅ Strengths

1. Consistent Null/Blank Handling: The PR correctly identifies and fixes the inconsistency where rewrite() returned "" for null but expandForKeywords() returned the original null value. Both methods now consistently handle null/blank inputs.

2. Improved Documentation: Replacing informal Korean comments with proper English Javadoc is excellent and follows Java best practices. The documentation clearly explains behavior, parameters, and return values.

3. Better Variable Naming: s → normalized is a clear improvement in code readability.

4. Comprehensive Test Coverage: 16 test cases covering edge cases, normalization behavior, and both methods is thorough and follows the codebase's testing conventions (@UnitTest, DisplayName).

💡 Suggestions

src/main/java/spring/memewikibe/infrastructure/ai/SimpleQueryRewriter.java:23-26

The implementation uses isBlank() check followed by trim() operations. This is redundant since isBlank() already verifies the string is empty after trimming. Consider:

if (query == null || query.isBlank()) {
    return "";
}
// query.isBlank() is false here, so trim() will always produce non-empty result
String normalized = query.toLowerCase(Locale.ROOT).replaceAll("\\s+", " ").trim();
return normalized;

Or more concisely:

if (query == null || query.isBlank()) {
    return "";
}
return query.trim().toLowerCase(Locale.ROOT).replaceAll("\\s+", " ").trim();

The second trim() after replaceAll() is still useful to handle edge cases where the regex might leave trailing spaces.

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Potential Bugs & Issues

⚠️ Behavioral Inconsistency with NaverQueryRewriter

src/main/java/spring/memewikibe/infrastructure/ai/SimpleQueryRewriter.java:40-44

There's a critical behavioral difference between SimpleQueryRewriter and NaverQueryRewriter:

• SimpleQueryRewriter.expandForKeywords(null) → returns ""
• NaverQueryRewriter.expandForKeywords(null) → returns null (see line 56 in NaverQueryRewriter.java)

This violates the Liskov Substitution Principle. Since these implement the same interface and can be swapped (NaverQueryRewriter is @Primary), they should have identical null-handling behavior.

Recommendation: Update NaverQueryRewriter.java:55-57 to return "" for null/blank inputs to match SimpleQueryRewriter's behavior:

if (query == null || query.isBlank() || naverApiKey == null || naverApiKey.isBlank()) {
    return "";  // Changed from 'return query;'
}

This ensures consistent behavior across implementations and prevents NPE in calling code.

✅ Good: No NPE Risk in Current Usage

I verified the usage in MemeVectorIndexService.java:111-112 and RecommendationService.java:83-84. Both locations use Optional<QueryRewriter>, so:

1. The methods are only called when a rewriter is present
2. The results (vectorQuery, keywordQuery) are used in subsequent operations

The current code is safe, but the behavioral consistency issue should still be addressed for future-proofing.

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Performance Considerations

✅ No Performance Concerns

The implementation is efficient:

1. Regex Compilation: \\s+ is a simple pattern that JVM optimizes well for String.replaceAll()
2. String Operations: Chained string operations are appropriate for this use case (queries are typically short)
3. No Heavy Operations: No I/O, no network calls, no complex algorithms

For typical query lengths (< 100 characters), performance is excellent.

💡 Minor Optimization (Optional)

If performance profiling later shows this as a hotspot (unlikely), consider using a pre-compiled Pattern:

private static final Pattern WHITESPACE_PATTERN = Pattern.compile("\\s+");

// Then use:
normalized = WHITESPACE_PATTERN.matcher(normalized).replaceAll(" ");

However, this is not necessary for the current use case. The PR is fine as-is.

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Security Concerns

✅ No Security Issues

1. No Injection Vulnerabilities: The method only performs string normalization, no code execution or command construction
2. No DoS Risk: String.replaceAll() with \\s+ pattern is safe and won't cause catastrophic backtracking
3. Input Validation: Proper null/blank checks prevent unexpected behavior
4. No Sensitive Data: Query strings are user-provided search terms, not credentials or secrets

The implementation is secure for its intended purpose.

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Test Coverage

✅ Excellent Test Coverage

src/test/java/spring/memewikibe/infrastructure/ai/SimpleQueryRewriterTest.java

The test suite is comprehensive and well-structured:

1. Edge Cases: null, empty, blank strings ✅
2. Core Functionality: normalization, trimming, space collapsing ✅
3. Character Handling: Korean text, special characters ✅
4. Both Methods: Tests for rewrite() and expandForKeywords() ✅
5. Test Structure: Follows AAA pattern (Arrange-Act-Assert) ✅
6. Naming: Clear, descriptive test names with @DisplayName ✅

💡 Suggested Additional Tests

Consider adding these edge case tests for completeness:

1. Mixed whitespace types: tabs, newlines, etc.

@Test
@DisplayName("rewrite: 탭과 줄바꿈을 공백으로 변환한다")
void rewrite_normalizesMixedWhitespace() {
    String result = queryRewriter.rewrite(null, "Hello\tWorld\nTest");
    assertThat(result).isEqualTo("hello world test");
}

2. Unicode normalization: Some Korean characters can be represented in multiple forms (NFC vs NFD). While not critical, it's worth considering if users might paste text from different sources.

3. Very long strings: Test with a 1000+ character query to verify no unexpected behavior.

However, these are nice-to-haves, not blockers. The current test coverage is already excellent.

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Summary & Recommendations

Must Fix (Before Merge)

None - the PR is safe to merge as-is.

Should Fix (Recommended)

1. Behavioral Consistency: Update NaverQueryRewriter.expandForKeywords() to return "" instead of null for null/blank inputs to match SimpleQueryRewriter's behavior.

Nice to Have

1. Remove redundant operations in the normalization logic (minor code cleanup)
2. Add tests for mixed whitespace types (tabs, newlines)
3. Consider adding JavaDoc example usage in the interface definition

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Conclusion

This is a high-quality maintenance PR that improves code safety, documentation, and test coverage. The identified issues are real, the solutions are appropriate, and the test coverage is excellent. The only concern is the behavioral inconsistency with NaverQueryRewriter, which should be addressed to ensure proper LSP compliance.

Recommendation: ✅ Approve (with follow-up fix for NaverQueryRewriter)

Great work on this cleanup! 🎉

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Review generated by Claude Code