Artemis: feat: Refactor LlmProxyController for improved readability and consistency

[mike-turintech]

This pull request introduces several minor refactors to the LlmProxyController aimed at improving code readability, consistency, and maintainability.

Key changes include:

• Introduce Constants: Extracted various hardcoded strings and MediaType objects into private static final constants.
• Consistent Timestamps: Ensured consistent timestamps by calling Instant.now() once per response/error building block.
• Explicit Character Encoding: Explicitly specified StandardCharsets.UTF_8 for string-to-byte conversions.
• Switch Syntax: Updated the syntax of a switch statement.
• Minor Variable Renaming: Renamed a variable for slightly better clarity.

These changes primarily improve code hygiene and maintainability without altering the core logic or API behavior.

Detailed Score Information

Score Details

This section contains detailed information about the performance scores for top 5 scored suggestions.

Top Performing Changes

1. src/main/java/com/llmproxy/controller/LlmProxyController.java:1-260 - Mean Improvement: 0.48, Mean Original Score: 4.26

• 🔴 Compatibility (Change: -0.03): The changes do not introduce any backward compatibility issues. All existing APIs and method signatures remain unchanged. Constants are refactored for better clarity, and only minor internal refactorings (like caching MediaType or adjusting error construction) are made. All input/output, endpoints, and contracts are preserved.

• 🔴 Equivalence (Change: -0.03): The logic and behavior are equivalent. Only minor refactors (reusing Instant.now() for consistency, introducing constants for error types, and using cached MediaType) are introduced. No functional changes are made; the structure, branching, and responses remain the same. The functionality is wholly preserved.

• 🟢 Performance (Change: +1.17): Several minor performance optimizations were introduced: constants like error strings and MediaTypes are hoisted and cached instead of being re-created each time in the method; byte[] encoding now specifies UTF-8 explicitly, which can also avoid platform charset inconsistencies and is slightly more efficient. The timestamp is now only generated once per error case or success, avoiding redundant Instant.now() calls. While none are groundbreaking, together these improvements can create a measurable, if modest, positive impact on server efficiency, especially under load.

• 🟢 Quality (Score: 4.97; Change: +0.60): The refactor improves code quality considerably: repeated string literals and magic values are replaced by well-named constants, improving maintainability and readability. The code is more DRY, with less repetition and clearer intent (such as extracting repeated error string and MediaType objects). The consistent use of Instant.now() at the top of each relevant code block and using named variables improves traceability and correctness (ensuring the same timestamp is reported across all parts of a response). Switch statements for status codes are expanded for clarity. Variable names are made more descriptive—e.g., changing 'response' to 'responseText' and 'responseBytes'—which makes the code easier to follow and maintain. Overall, the updated code is significantly more maintainable and robust.

• 🟢 Value (Change: +1.17): The changes bring significant improvements to the codebase through several optimizations and best practices: 1) Constants are extracted for error messages and media types to avoid string duplication and improve maintainability, 2) Instant objects are reused instead of repeatedly calling Instant.now(), reducing object creation, 3) StandardCharsets.UTF_8 is explicitly used for string-to-byte conversions instead of relying on platform-default encoding, 4) The switch expression is converted to a traditional switch statement for broader compatibility, 5) Variable names are improved for clarity (response → responseText), and 6) Response bytes are computed once and stored rather than repeatedly generating them. These changes reduce memory allocations, improve code readability, and make the code more maintainable while maintaining the same functionality.