How to open a JNLP file. A few days ago, the boss asked him to analyze some files with the help of a specific program previously loaded in a pen drive. However, once you connected the device to the PC, you noticed that the application in question is in format JNLP, an extension that you have never seen before and, consequently, simply cannot manage.

In order to avoid a good conference and finish the work that was assigned to him as soon as possible, he immediately opened Google looking for information about how to open a JNLP file, ending right in this my guide. Well, I want to tell you right away that you are in the right place, at a time that couldn't have been better! However, before continuing, let me give you more information on the subject. The JNLP extension identifies a particular type of file designed to launch software written in Java, whose code resides in Internet.

This type of application does nothing more than download the code of the program in question to the PC, starting immediately after the first valid instruction for its execution. In other words, a JNLP file is nothing more than the "starter" of a So Java Program. To start it correctly, you must first install a Java environment on your work PC. In the next few lines, I will take care of explaining how to do it in both Windows and macOS. I guarantee that by carefully following the instructions that I am going to provide you.

How to open JNLP files in Windows

As I already mentioned in the introductory lines of this tutorial, the files JNLP they are "launchers" of web applications written using language Java. Within them, they contain information related to the Internet address where the executable file of the real program is located, as well as the initial class to invoke (that is, the first useful "instruction" to start the execution flow of the Java application in question)

In other words, a JNLP file is nothing more than the initiator of a program written in Java, residing somewhere on the Internet. Consequently, to properly open this type of file (and the program with which it is associated) it is essential to have a Java environment previously installed on the PC.

Java installation

If you have Windows, and you want  open files JNLP but you have not done the Java installation yet, you can run the coverage as follows: first, connected to the Java website, press the button Accept and continue to comply with the legislation on cookies. Then click the button Java free download, to access the software installation page.

At this point, click on the button Accept and start the free download to immediately download the installation file (eg. JavaSEuXXXX.exe ) in the PC. And after the download is complete, launch the mentioned program and press the button yes to immediately start the Java environment setup procedure.

Then, press the button install to confirm the willingness to proceed and if an announcement regarding the Oracle Java SE roadmap appears, press the button you accept to confirm that you have read it. From now on, the installation of the Java environment should be done automatically. You can check the progress through a green bar attached to the window displayed on the screen. Finally press the Open button located in the warning window related to the completion of the installation.

It is said that the game, now at this stage, is practically done: place the PC on the PC JNLP file you want to start and double click on it, exactly as you would to start any other program: after a few seconds, if everything went well, you should see a security notice related to file execution.

If the file doesn't open, you can right-click its icon and select the item. Open with…> Other / Other applications from the proposed menu: when you get to the selection panel, select the application Java (TM) web launcher from the list of available programs.

After making sure that the author of the post is trustworthy, click the RUN button to confirm the desire to open the program in question and wait for the corresponding Java application to open. That is all!

note : Pay attention to JNLP files, as Java applications on the Internet may contain unwanted surprises like viruses, malware, etc. Therefore, to avoid accidental damage to your data or Pc, be sure that start only the files you know where they come from.

In case of problems

Wait, are you telling me that you failed open files JNLP using the technique suggested above, even though you followed all the provided instructions in a slavish way? Then you may need to 're-associate' the JNLP extension for execution via Java, in order to communicate to the operating system the application with which to open the file type in question.

How? Simple: first, right-click the JNLP file in question, click the item your property attached to the proposed context menu, open the tab general and press the button Change ... in the section To open with.

At this point, click on the items. Other apps … y Search for other applications on this PC and, using the File Explorer / Windows Explorer panel displayed on the screen, I went to the folder containing Java executable files (which, in most cases, is C: Program Files (x86) Java jrexxx_yyy bin o C: Program Files (x86) Java jrexxx_yyy bin ). Then select the file javaws.exe with a double click. Finally press the accept button, in the properties screen of the file and try to run it again with a double click: the result is guaranteed!

How to open JNLP files on Mac

One of the strengths of programs written in Java is their cross-platform nature. These types of applications, in fact, can be run on any operating system that has been previously installed in a Java environment. Consequently, exactly as seen for Windows, the first thing to do to open JNLP files on macOS is to proceed with the installation of the entire Java system.

How? Very simple: once again, you must initially connect to the Java download page. Then clicking the button Accept and continue to consent to the use of cookies. After that click the button Java free download and repeat the operation with the button Accept and start the free download attached to the following screen.

Once the installation file is obtained (eg. jre-xxx-macosx-x64.dmg ), run it without hesitation and double-click the package icon located in the window that appears on the screen to start the Java environment installation procedure.

At this point, click on the button openwrite the password of Mac in the next text box press the button Installation wizard and follow the on-screen instructions to continue. What you should do is click on the buttons install (repeating the operation, if necessary, in the accept located inside the dialog box related to the Oracle Java SE roadmap) and open to complete the installation procedure.

At this stage, all you have to do is locate the JNLP file you are interested in opening, select its preview by right-clicking. Click Open, from the proposed menu and confirm the desire to open the file by pressing Open. You should do this only the first time you open the file, to "bypass" the restrictions imposed by macOS against applications from non-certified developers.

If everything went in the right direction, the system should show a summary screen in the application you are trying to open. If the author of the post is consistent with what you expect, press RUN or run   to immediately start executing the file and you're done.

In case of problems

If, after trying to open a JNLP file following the instructions illustrated above, absolutely nothing happens. You may need restore associations files of this type, thus indicating to the operating system the correct program that will be used to open them (in this case, the Java launcher).

To do it is very simple. First, right-click on a JNLP file anyone. Select the item Get information from the proposed context menu and expand the section To open with by clicking on the corresponding arrow. Then, from the drop-down menu located just below, select the item Plus … and wait for the window to choose the program that will be used to open the document.

At this point, move the top drop-down menu (initially identified by the item applications ) in option Mac for (Your name). Choose Mac disk from the left part of the window and, using the adjacent panels, go to the folder System> Library> CoreServices then select the application Java Web Start from the list in the right pane. If it cannot be selected, be careful to configure the option All applications in the drop-down menu allow.

When you're done, press the button Add and for all JNLP files to start with the same app press the buttons Edit everything … y follow.

Problems and errors

After trying open a JNLP file Did you come face to face with a disturbing error message? So the problem could be due to the digital signature associated with the file itself.

By default, the Java application execution policy in macOS is much more restrictive than that established in Windows. For this reason, some applications that do not have a valid digital signature may not work. Addressing this drawback is relatively simple: In fact, it is possible to ensure that control over digital signatures is not performed at all, so that you can run any type of JNLP file without compromising security-related errors.

However, be aware that doing so could compromise system security, as JNLP files that do not have a valid signature It could represent a danger to the integrity of the data and the PC.

 Do you want to continue anyway? OK no problem. First, log in to adjustments Mac pressing the icon in the form of gear attached to the bar dock. Select the item Java and wait for the configuration panel to open automatically. If this doesn't happen, do it yourself by pressing the button Reopen the Java Control Panel.

At this point, click on the tab advanced.  Put a check mark next to the item Do not verify (not recommended ) corresponding to Perform revocation checks of signed code certificates. And repeat the operation with the same element corresponding to the section Perform TLS certificate revocation checks on. Finally remove the check mark from the entry Enable exclusion list revocation verification. AND make the changes effective by pressing the buttons apply y good.

Once this is complete, try again on open JNLP files of your interest through the procedure illustrated above: you should no longer have problems!