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feat: implement size-limited LRU cache for JSON Schema validation by joaquinescalante23 · Pull Request #845 · modelcontextprotocol/java-sdk · GitHub

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feat: implement size-limited LRU cache for JSON Schema validation - #845

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joaquinescalante23 wants to merge 1 commit into
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joaquinescalante23:fix/json-schema-cache-resilience
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feat: implement size-limited LRU cache for JSON Schema validation#845
joaquinescalante23 wants to merge 1 commit into
modelcontextprotocol:mainfrom
joaquinescalante23:fix/json-schema-cache-resilience

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joaquinescalante23 commented Mar 4, 2026

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I noticed that the current DefaultJsonSchemaValidator implementations (Jackson 2 and 3) were using an unbounded ConcurrentHashMap for schema caching, which could lead to memory leaks in long-running processes if exposed to a large number of dynamic schemas.

This PR addresses the TODO in both modules by:

  • Replacing the unbounded map with a thread-safe LRU Cache (defaulting to 1024 entries) using LinkedHashMap.
  • Making the cache size configurable via constructors for greater flexibility.
  • Improving the generateCacheKey logic to use a stable JSON representation of the schema instead of the default hashCode(), preventing potential collisions and ensuring cache hits are reliable regardless of map order.

These changes significantly improve the resilience and resource management of the SDK when validating complex MCP tool outputs.

joaquinescalante23 commented Mar 4, 2026

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I've been following the architectural changes proposed in PR #749 by @tzolov. While that PR focuses on the extensibility of the validator through suppliers, this PR addresses a critical resource management issue in the current default implementation.

Specifically, the existing DefaultJsonSchemaValidator (Jackson 2 and 3) lacks a cache eviction policy, which poses a memory exhaustion risk in long-running applications or when dealing with dynamic tool schemas. My proposal introduces a size-configurable LRU Cache that would make the new supplier-based architecture much more robust by default.

I'm happy to rebase or adjust this PR to align with the new supplier patterns once #749 is merged. Let me know if you'd like me to integrate these resilience improvements into the new supplier structure!

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