JNLP is a type of file used with Java Web Start. This is a setup that permits users to download Java applications from the Internet and run them with a single click, rather than contending with a more complicated installation process. Unlike most files, you'll normally open a JNLP file through a Web link rather than from your computer's file management system.
Java Web Start
In order to use JNLP files, you'll need to have Java Web Start on your computer. You can get it as part of the overall Java package, downloadable from the Java website (see Resources). Once you have Java Web Start on your computer, it will automatically download and install any JNLP file you obtain from the Internet. After installation, the next time you select a JNLP file, Java Web Start will check for the latest version and it will update the file and run it.
Normally, selecting a JNLP file should automatically open it using Java Web Start. If this doesn't happen, the file association may be missing or corrupted. You can change this through the Windows Settings menus. In Windows 8, you need to search for "Default Programs" and select it from the results under "Apps". Next, select "Associate a file type or protocol with a program" and select ".JNLP" from the list and then select "Change program." You will see "Java Web Start Launcher" among the list of programs, so select it. If you don't see it listed, select "More Options" and then "Look for another app on this PC." Then select the file "javaws.exe," which you'll normally find by following the folders "C: | Program Files (x86) | Java | JRE7 | bin." If this doesn't work, you may need to try the folder "Program Files" (without x86) or "JRE" with a later number.