Application class data sharing (CDS) in Java 10

24 Oct 2023

Java 10 introduced a new feature called Application Class Data Sharing (CDS), which aims to improve the startup time of Java applications. CDS allows classes and resources to be shared between different Java processes, reducing the amount of time it takes to load classes and initialize the JVM. In this blog post, we will explore how to use CDS in Java 10.

Application Class Data Sharing (CDS) is a mechanism that enables the sharing of classes, resources, and metadata between different Java virtual machine (JVM) instances. This sharing allows JVMs to start up faster and use less memory.

Traditionally, each JVM process loads classes individually, resulting in duplicate class loading and initialization overhead. With CDS, a predefined set of classes and resources can be shared and mapped into the JVM’s memory directly, avoiding the need to load them again.

How to use CDS in Java 10?

To use CDS in Java 10, you need to follow these steps:

1. Create a class list file

First, you need to create a text file that lists the classes and resources you want to share. Each class or resource should be on a new line. You can use the java.util.ServiceLoader class to generate this file automatically:

java -XX:+UseAppCDS -XX:DumpLoadedClassList=myclasslist.txt <your-application-jar-file>

Make sure to replace <your-application-jar-file> with the path to your application’s JAR file. The -XX:+UseAppCDS option enables CDS, and the -XX:DumpLoadedClassList option specifies the file name to generate.

2. Create a shared archive file

Next, you need to create a shared archive file based on the class list file you created in the previous step. To create the shared archive file, use the following command:

java -XX:+UseAppCDS -XX:SharedArchiveFile=myapp.jsa -XX:SharedClassListFile=myclasslist.txt

The -XX:SharedArchiveFile option specifies the file name for the shared archive file, and the -XX:SharedClassListFile option specifies the class list file generated in the previous step.

3. Use the shared archive file

Finally, when starting your Java application, include the -XX:+UseAppCDS -XX:SharedArchiveFile=myapp.jsa options to use the shared archive file:

java -XX:+UseAppCDS -XX:SharedArchiveFile=myapp.jsa -jar <your-application-jar-file>

Replace <your-application-jar-file> with the path to your application’s JAR file.

Benefits of CDS

Using CDS in Java 10 can bring several benefits, including:

Improved startup time: By sharing and reusing preloaded classes and resources, the JVM startup time can be significantly reduced.
Reduced memory footprint: Sharing classes and resources between JVM instances can lead to a smaller memory footprint, as less memory is needed to store duplicated class data.
Enhanced performance: With faster startup times and reduced memory usage, overall application performance can be improved.

Conclusion

Application Class Data Sharing (CDS) is a powerful feature introduced in Java 10 that can greatly improve the startup time and memory footprint of Java applications. By leveraging CDS, you can significantly enhance the performance of your Java applications. Give it a try and experience the benefits it offers.

References:

Java Platform, Standard Edition (Java SE) API Specification: https://docs.oracle.com/javase/10/docs/api/

#java #java10

What is Application Class Data Sharing?