JarOpt — Automated JAR Optimization for Production Builds

JarOpt Tips & Tricks: Reducing Footprint and Improving Performance

What JarOpt does

JarOpt analyzes and optimizes Java JAR files to reduce size and improve runtime performance by removing unused classes/resources, compressing contents, and applying bytecode-level optimizations.

Key techniques and how to use them

1. Tree-shaking unused classes

   • What: Detect and remove classes/methods not referenced at runtime.
   • How: Run JarOpt with static analysis enabled; verify with an instrumented test suite to catch reflection usage.
   • Tip: Use keep rules for reflection-heavy libraries (e.g., serialization frameworks).

2. Strip unused resources

   • What: Remove images, text files, and metadata not required in production.
   • How: Configure resource filters by path/glob patterns; run a dry-run to list removals.
   • Tip: Externalize large assets to a CDN when feasible.

3. Aggressive compression

   • What: Apply optimal ZIP compression levels and pre-compress large text assets.
   • How: Enable maximum deflate or use Brotli for resources served separately.
   • Tip: Measure decompression CPU cost vs. bandwidth savings for your target environment.

4. Bytecode optimization

   • What: Inline small methods, remove dead code, and optimize constant folding.
   • How: Enable JarOpt’s bytecode passes; test thoroughly for edge-case behavior changes.
   • Tip: Keep a baseline performance test to ensure optimizations help real workloads.

5. Class-data sharing and modularization

   • What: Use CDS/AppCDS and split into smaller modules to improve startup.
   • How: Generate shared archives with JarOpt-compatible flows; modularize large monoliths.
   • Tip: Warm-up caches in CI to produce stable CDS snapshots.

6. Dependency pruning and relocation

   • What: Remove or replace heavy transitive dependencies; relocate packages to avoid conflicts.
   • How: Analyze dependency graph, exclude unused artifacts, and use shading/relocation tools.
   • Tip: Prefer lighter alternatives (e.g., java.util vs. Guava) where practical.

7. Minimize classloader overhead

   • What: Reduce number of JARs on classpath and flatten classloader hierarchies.
   • How: Merge related JARs and use a single classloader for tightly-coupled modules.
   • Tip: Beware of increased JAR size vs. classloader savings trade-off.

8. Optimize startup-critical code paths

   • What: Defer nonessential initialization and lazily load components.
   • How: Convert eager singletons to providers; use lazy holders or Supplier-based factories.
   • Tip: Profile startup to identify hotspots before changing initialization order.

Testing and verification

• Automated tests: Run unit/integration tests after each optimization pass.
• Benchmarking: Use realistic workloads and measure startup time, memory, and throughput.
• Sanity checks: Validate reflection, serialization, and native interop behavior.

Recommended workflow

1. Baseline: measure current size and performance.
2. Apply safe passes: resource stripping, compression.
3. Run tests and benchmarks.
4. Apply aggressive passes: tree-shaking, bytecode optimizations.
5. Verify in staging and generate CDS if beneficial.
6. Release with rollback plan.

Quick checklist before release

• Keep rules for reflection/serialization checked.
• Run full test suite and smoke tests.
• Verify licensing when removing or modifying third-party code.
• Produce rollback build and document optimization steps.

If you want, I can generate a JarOpt config file with conservative keep rules and a test plan tailored to a typical Spring Boot app.