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JaveOne 2025
18/03/2025

JaveOne 2025

OpenJDK Project Leyden is an effort to make Java apps start faster, reach peak performance sooner, and use less memory—b...
23/09/2024

OpenJDK Project Leyden is an effort to make Java apps start faster, reach peak performance sooner, and use less memory—by moving part of the JVM’s work from run time to ahead-of-time (AOT) “training” and caching. It’s sponsored by the HotSpot and Core Libraries groups.

What’s already in the JDK
JDK 24 – JEP 483: AOT class loading & linking. A “training run” records what classes are needed, then creates an AOT cache so production runs can skip parsing/loading/linking at startup.
JDK 25 – JEP 514: Easier CLI ergonomics (e.g., AOTCacheOutput to record+create a cache in one step).
JDK 25 – JEP 515: AOT method profiling, so production runs warm up faster using recorded profiles.
In progress – JEP 516: AOT object caching that works with any GC (GC-agnostic format).

How it works (at a glance)
Train/record on a representative run → 2) Create an AOT cache → 3) Run with the cache to avoid much of startup work (and use recorded profiles). This complements CDS and runs on the standard HotSpot JVM—no closed-world constraints.
Try it quickly
JDK 24 (JEP 483):

# training + create
java -XX:AOTMode=record -XX:AOTConfiguration=app.aotconf -cp app.jar com.example.App
java -XX:AOTMode=create -XX:AOTConfiguration=app.aotconf -XX:AOTCache=app.aot -cp app.jar

# production run
java -XX:AOTCache=app.aot -cp app.jar com.example.App

JDK 25 (JEP 514):

java -XX:AOTCacheOutput=app.aot -cp app.jar com.example.App # record + create in one
java -XX:AOTCache=app.aot -cp app.jar com.example.App # use cache

06/12/2023

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