257. Introducing Application Class Data Sharing (AppCDS, or Java’s Startup Booster)

Launching a Java application is a multi-step process. Before executing the bytecode of a class, the JVM has to perform at least the following steps for a given class name:

1. Look up the class on disk (JVM has to scan the disk and find the given class name).
2. Load the class (JVM opens the file and loads its content).
3. Check the bytecode (JVM verifies the integrity of the content).
4. Pull the bytecode internally (JVM transfers the code into an internal data structure).

Obviously, these steps are not cost-free. Loading hundreds/thousands of classes will have a significant overhead on launching time and memory footprint. Typically, an application’s JAR remains unchanged for a long time, but JVM performs the previous steps and obtains the same result every time we launch the application.

Improving/accelerating the startup performance and even reducing the...