Java Web Start

In computing, Java Web Start (also known as JavaWS, javaws or JAWS) is a framework developed by Sun Microsystems (now Oracle) that allows users to start application software for the Java Platform directly from the Internet using a web browser. Some key benefits of this technology include seamless version updating for globally distributed applications and greater control of memory allocation to the Java virtual machine.

Unlike Java applets, Web Start applications do not run inside the browser. By default they run in the same sandbox as applets, with several minor extensions like allowing to load and save the file that is explicitly selected by the user through the file selection dialog. Only signed applications can be configured to have additional permissions.

Web Start has an advantage over applets in that it overcomes many compatibility problems with browsers' Java plugins and different JVM versions. Web Start programs are no longer an integrated part of the web page, they are independent applications that run in a separate frame.

Web Start can also launch unmodified applets that are packaged inside .jar files, by writing the appropriate JNLP file. This file can also pass the applet parameters. Such applets also run in a separate frame. Applet launcher may not support some specific cases like loading class as resource.

Like applets, Java Web Start is cross-platform.

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.

...
Wikipedia