Implementation
The developer prepares a special XML file with JNLP extension. This file describes the application requirements, code location, parameters and additional permissions (if any). The browser downloads this file as any other and (following its MIME type, application/x-java-jnlp-file) opens it with Web Start tool. Web Start tool downloads all necessary resources and launches the application.
Java Web Start provides a series of classes in the javax.jnlp package which provide various services to the application. Sun designed most of these services with the aim of allowing carefully controlled access to resources (such as files and the system clipboard) while restricting the application to authorized operations.
Sun introduced version 1.0 of Web Start in March 2001, while 64-bit Windows support added only in Java 6 (later than 64-bit Java was first available). Since J2SE 1.4 Web Start comes as a default part of Java Runtime Environment (JRE) called javaws, and computer administrators no longer have to install it separately.
Read more about this topic: Java Web Start