Java 10 - Class-Data sharing

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JEP 310 − Application Class-Data Sharing

When JVM starts it loads the classes in memory as a preliminary step. In case there are multiple jars having multiple classes, an evident lags appears for the first request. In serverless architecture, such a lag can delay the boot time which is a critical operation in such an architecture. Application class-data sharing concept helps in reducing the start up time of an application. Java has an existing CDS (Class-Data Sharing) feature. With Application class-data sharing, Java 10 allows to put application classes in a shared archive. This reduces the application startup and footprint by sharing a common class meta data across multiple java processes.

Process

Application Class data sharing is a 3 step process.

  • Create a list of Classes to archive − Create a list welcome.lst of a class Greeting.java lying in welcome.jar using Java Launcher.

$java -Xshare:off -XX:+UseAppCDS -XX:DumpLoadedClassList=welcome.lst -cp welcome.jar Greeting
  • Create AppCDS archive − Archive a list of classes to be used for Application class data sharing.

$java -Xshare:dump -XX:+UseAppCDS -XX:SharedClassListFile=welcome.lst -XX:SharedArchiveFile=welcome.jsa -cp welcome.jar
  • Use AppCDS archive − Use AppCDS archive while using java launcher.

$java -Xshare:on -XX:+UseAppCDS -XX:SharedArchiveFile=welcome.jsa -cp welcome.jar Greeting
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