JNLP, which stands for Java Network Launching Protocol, is not a network protocol, although its name seems to suggest otherwise. In fact, it is the file extension that is generally used to create Java applications designed for the Java Web Start framework. Any information accessed remotely via Java Web Start is acquired only using the standard web protocol, HTTP.

Understanding JNLP Files Better

As mentioned before, in order to run them, users need to download Java applications to their computer, and it is this downloadable file of the Java application that carries the .jnlp extension. JNLP files are of the XML file format. Although the Java Network Launching Protocol is the name of the extension and not an actual protocol, it sort of symbolically represents a protocol used to access remotely located files. Essential files that are required to run the Java application are stored on the remote Java server. The JNLP client, namely the Java Web Start framework, retrieves these remotely located files, and then takes on its primary role of launching the Java application. Of course, the application cannot run unless the Java Runtime Environment (JRE) exists on the user's computer. The purpose of this client-server architecture implemented by Java is not merely to launch applications, but to have complete control over their management. For example, the server can make different features available to different clients, based on certain discerning factors like location.

How To Open a JNLP File

JNLP files are automatically launched by Java Web Start, if an attempt to open them on a computer, on which any version of Java has been installed, is made. The process is so quick that the Java application will immediately run as soon as the link to it is clicked from a compliant, and well-equipped browser (such as Google Chrome or Mozilla Firefox). However, sometimes Java Web Start may not be specified as the default application to open JNLP files, and because of this you may not be able to open the file that you want. Here are the steps to follow to open a JNLP file that refuses to run automatically. 1. Locate the file you wish to open that has the .jnlp extension, on your computer. 2. Right-click on the icon of the file, and select Properties from the menu that drops down. 3. In the Properties window of the .jnlp file, select the General tab. 4. Check whether the name of the application listed next to the 'Opens with:' attribute is Java (TM) Web Start Launcher. If it is stated as javaws.exe too, it is referring to the same program. 5. The application program listed here is the default one that your computer uses to open JNLP files. If it is not Java (TM) Web Start Launcher, you need to change this setting. Click on the button labeled 'Change', located right next to the listing. 6. In the window that opens, peruse through the list of programs that Windows suggests you can open such files with, and locate javaws. 7. If you cannot locate it in the list, click the button labeled 'Browse' that is located below the list of applications. 8. In the browsing window that allows you to pick the application you want, open the following path: Java Web Start is a part of the Java Runtime Environment package, and gets downloaded along with it onto your computer. However, if you have downloaded it separately from Oracle's Java website, you may also find the javaws.exe application program at this path: 9. In this folder, double-click on the application named javaws. 10. Back in the Properties window, click on the button labeled 'Apply' located at the bottom of the window. The default application with which JNLP files will be launched on your computer has now been explicitly set as Java Web Start. If you are unable to open Java applications on your computer, ensure that the Java Runtime Environment has been installed on your computer properly. You can download it for free from java.com. If necessary, download Java Web Start Launcher separately from Oracle's website. Another reason for the problem of being unable to open JNLP files may be that, the feature of launching them itself may be blocked. Here is how you can unblock it: 1. Open the Start menu. 2. In the Start menu, locate and click on Control Panel. 3. Inside your computer's Control Panel, click on Programs. It is located right at the bottom of the window. 4. Locate and click on Java. This will open up the Java Control Panel window. It is an application that exclusively allows you to manage and modify settings related to Java. 5. Click on the tab labeled 'Advanced'. 6. From the list of settings, find 'JNLP File/MIME Association'. From the options, select either 'Prompt user' or 'Always allow'. If the setting is 'Never allow', your computer will never be able to run a JNLP file.