JEP 483: Ahead-of-Time Class Loading and Linking

JEP 483 introduces an Ahead-of-Time (AOT) class loading and linking feature aimed at improving the startup time of Java applications. By monitoring an application during a single run, the HotSpot Java Virtual Machine (JVM) can cache the loaded and linked forms of classes for future executions. This approach leverages the repetitive nature of application startups, where similar classes are loaded and linked each time. The AOT cache allows for a significant reduction in startup time without requiring changes to application code or command-line execution methods. The process involves two main steps: first, a training run to record the application's configuration, and second, the creation of the cache based on this configuration. The AOT cache can lead to performance improvements of up to 42%, as demonstrated with applications like Spring PetClinic. However, it is important that the training run closely resembles production runs to maximize the cache's effectiveness. The feature is built on the existing class-data sharing (CDS) mechanism, enhancing it by not only caching class metadata but also the actual loading and linking processes. This development aims to provide a foundation for further optimizations in both startup and warmup times for Java applications.

- JEP 483 aims to improve Java application startup times through AOT class loading and linking.

- The AOT cache stores loaded and linked class forms for faster access in subsequent runs.

- Performance improvements of up to 42% have been observed with applications using the AOT cache.

- The feature does not require changes to application code or command-line execution.

- Consistency between training and production runs is crucial for the effectiveness of the AOT cache.