The file extention .jnlp file is used as a package that neatly bundles all the necessary information required to download and/or execute a remote application. See picture below :
File Extension .jnlp use for java web programming, for Java Web Start itself is only about 1 MB. However, it requires the Java Runtime Environment (JRE), so if a you (or a user) don't have a JRE, the download size increases accordingly, to just under 6 MB on Microsoft Windows platforms.
Java Network Launch Protocol (JNLP) are a standard part of the Java 2 platform (as of version 1.4), it's far easier to deploy cross-platform, client-side systems.
http://www.fileextensionjnlp.net/
