Supercharge your JVM performance with Project Leyden, by Ana Maria Mihalceanu

Project Leyden is a JVM initiative aimed at reducing Java startup and warm-up times through ahead-of-time (AOT) caching based on training runs. JDK 24 introduced a three-phase workflow (record, assemble, deploy), while JDK 25 simplified this to a two-phase workflow and added method execution profile caching. Benchmarks show up to 62% startup improvement on plain JDK 24, with additional gains from AOT caching. For Spring Boot applications, using jar-mode extraction and the `exitOnRefresh` flag further improves results. Practical requirements include matching JDK version and hardware architecture between cache creation and production, preserving jar timestamps, and keeping classpath consistent. Operational patterns for Docker and Kubernetes are discussed, including separating cache generation into a privileged builder container and reusing the cache in a lean runtime container. JDK 26 will extend AOT support to ZGC and improve AOT code compilation. Static analysis approaches remain on the roadmap but training runs are the current focus.