Feature: Cache ClassLoader for pluginDir

[infeo]

This PR changes the loading of plugins.

Currently, calling IntegrationsLoader::loadX method creates a new class loader. The class loader completely traverses the pluginDirectory. If there are many plugins or deeply nested ones, loading specific services takes a long time. Every time a certain service is loaded.

This PR adds a thread-safe, lazily initialized cache for the class loader, which is initialized once and never invalidated. It reduces the look up time of consecutive service implementations and ensures that only one file handle to each plugin file is created.

Important implication is, that once any service is loaded, changes to the plugin directory or the plugin directory property have no effect.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 09ce1ffa-a363-4f90-813e-864cf895325d

📥 Commits

Reviewing files that changed from the base of the PR and between e833e27 and 71bcf11.

📒 Files selected for processing (2)

• src/main/java/org/cryptomator/integrations/common/ClassLoaderFactory.java
• src/main/java/org/cryptomator/integrations/common/IntegrationsLoader.java

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Walkthrough

The changes introduce a cached, lazily-initialized plugin ClassLoader in IntegrationsLoader through a new inner class PluginClassLoaderHolder and corresponding accessor method. This replaces repeated direct calls to ClassLoaderFactory.forPluginDir() with a single shared instance. Additionally, Javadoc for ClassLoaderFactory.forPluginDir() was updated to clarify that the returned URLClassLoader loads classes from the "given directory" rather than "given classes."

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• Disable plugin loading on illegal/ not set plugin dir #86 — Modifies the same ClassLoaderFactory.forPluginDir() classloader acquisition path that this PR replaces with a cached instance.

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: caching a ClassLoader for the plugin directory, which is the core objective of the pull request.
Description check	✅ Passed	The description is directly related to the changeset, explaining the motivation, implementation approach, and implications of caching the ClassLoader for plugin loading.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feature/cache-classloader

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