JSA is abbreviated for `Java Shared Archive`. Conceptually it is called as Class Data Sharing.
Overview from Oracle Site
Class data sharing (CDS) is a new feature in J2SE 5.0 intended to reduce the startup time for Java programming language applications, in particular smaller applications, as well as reduce footprint. When the JRE is installed on 32-bit platforms using the Sun provided installer, the installer loads a set of classes from the system jar file into a private internal representation, and dumps that representation to a file, called a "shared archive". Class data sharing is not supported in Microsoft Windows 95/98/ME. If the Sun JRE installer is not being used, this can be done manually, as explained below. During subsequent JVM invocations, the shared archive is memory-mapped in, saving the cost of loading those classes and allowing much of the JVM's metadata for these classes to be shared among multiple JVM processes.
