Using jarfix.exe to fix .jar file association when SAB/RAB/DAB won’t start in Windows

I’ve helped a few colleagues who have had the problem that nothing happens when they try to launch SAB/RAB/DAB from their menu, icon, or whatever calls the *-app-builder.jar file. A tool that has fixed this issue of a computer not recognizing what to do with a .jar file (or doing the wrong thing with a .jar file) is a utility called jarfix.exe published as freeware by Johann Johann Löfflman. As his webpage describes,

“on Windows any program can steal a file type at any time even if it is already associated with a program. Many zip/unzip programs prefer to do this, because a jar is stored in the .zip format. If you doubleclick on a .jar, your pack program opens the file, rather than javaw runs the program, because your pack program ignores the meta information which are also stored in a .jar

You can fix this problem very easy with the small but reliable jarfix.exe program. Just doubleclick on it to restore the .jar association with javaw.exe.”

I’ve seen this problem more than a few times; every time we have an app-builder workshop (which usually include 15-20 participants) we seem to have one or two people whose machines can’t open .jar files correctly. Repairing the file association with this tool has solved the problem a lot of the time, so I wanted to document it here and suggest that it might be good to even include this in the troubleshooting section of the installation instructions.

1 Like

This seems to be the most common installation problem.

Yes I have used jarfix.exe a few times but only in person. Not remotely. The link you provided looks a reputable site. Though many are afraid of command line programs.

I also ask people to look at Default Apps (from Settings > Apps > Default Apps) and there is a link there after that short list of apps to Choose default apps by file type. Look at the .jar file type and if you have installed Amazon Corretto Java then choose OpenJDK Platform Binary.

I am setting up a new laptop and installing various programs that I used on my previous computer. I tried to install SAB just now and all it does is try to open/download the .jar in Firefox. When I look at the Default Apps and find the .jar file type, for some reason it has Firefox as the app to “open” this type of file and there are no other options besides finding an app in the Microsoft store.

Any recommendations? I downloaded and installed Java and restarted computer and re-installed SAB but still keeps trying to open the .jar file with Firefox.

Did you try and change the .jar file association as I outlined?

Yes, the only options when I click on .jar file type are Firefox (current selection) and Look for another app in Microsoft store…

Not sure what else to do. I’ve been using SAB for 5 years and this is first time I’ve installed/upgraded and had any issue like this.

Does it start if you use sab.bat? If not send me a copy of your sab.bat. What is the path to your Java JRE?

Did you use an installer? What Java source and version do you have installed? Do you have a 4K screen?

I try and avoid having people poking in their Registry, but you need to dig deeper.

Assuming you are using the latest SAB recommendation to use Azul Java, when you open Regedit do you have an entry?


Of course if you are still using Corretto or Oracle Java then you will have something related to that. I don’t have Corretto installed anymore but still have a similar entry for that.

Then the .jar association in Computer\HKEY_CLASSES_ROOT.jar should look like this:

That is the basics of file association, but Registries are complex and other things can undermine that setup.

1 Like

Thanks for these extra instructions…most of them were un-necessary after re-visited the Installation Instructions and realized that in switching to my new computer, I hadn’t gone through the full installation instructions.

However, I do have a 4k monitor and see that is a separate issue with Java 8 and I’ve been viewing that thread:

I’m not a great instruction reader/follower. However I know that the SAB installation instructions are written well and need to be followed step by step to set up your developer environment. While you don’t need to code, you need a developer environment for SAB to work in. Setup is harder than building the app.

(This is aimed at me and other experienced users) Also remember that when doing a new install you need to reread the instructions as some things change with new releases.

I used the jarfix.exe to get SAB working. Windows 10 Home version associated the .JAR with Adobe Acrobat Reader. The person I was helping had downloaded the .ZIP version of the JDK install, so I had them download the .msi version and reinstall. Not sure if that was necessary.

User now has issue with Aeneas installing properly, but will look through forum to see if there are solutions.

Thank you for the solution. It worked for me.

The 8.6.x SAB Windows versions have a JRE included in the installer to get around the hijacked .jar association and to improve the display for the ones with 4K screens. So Jarfix should be a thing of the past.