Instrument to Remove: Using Java agents for fun and profit
summary
A small Java agent prototype instruments classes by inserting a static initializer via javassist bytecode insertion to record class usage, then appends a runtime jar into the bootstrap loader with appendToBootstrap runtime jar so instrumented code can call back into the agent. Running on Spring PetClinic (56 MB jar, ~30,000 classes) it observes ~12,000 loaded and ~9,000 actually initialized (PetClinic: 56MB → 9,000 used classes), writes usage lists for manual removal or pre-instrumented jar rewriting, and exposes an agent control port for inspection.
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chapters (14)
- 0:00Java agents and de-bloating
- 4:16Limitations of existing tools
- 8:11Nerd sniping and new tool
- 10:15Unused classes for de-bloating
- 16:17Java agent basics
- 20:38Java agent implementation
- 24:49Class loader challenges
- 26:57Agent startup timing
- 28:20Bytecode libraries and techniques
- 30:05Demo and results
- 32:10Debugging Mockito
- 33:54Agent design patterns
- 36:21Summary and resources
- 37:26Q&A on agents
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