How to create a .jar association for your OpenJDK

From Java 11, Oracle has changed the license of their JDK, so you probably may want (or even have) to move to OpenJDK, and if you have moved already to OpenJDK, you may have noticed that clicking on a .jar didn't work anymore as it did with Oracle JDK binaries. This is because most of the pre-build OpenJDK binaries are coming without an installer on Microsoft Windows. Fortunately, it is easy to fix - with jarfix.

In the following example I show you how to use jarfix in order to setup the .jar association for your OpenJDK.


1. Download the OpenJDK

Download the OpenJDK from the source of your choice. You could get it from http://jdk.java.net/ or https://adoptopenjdk.net for example. Actually there are many more sources where you can get it, but I have downloaded the latest OpenJDK from https://adoptopenjdk.net, and extracted the .zip file to C:\Applications\jdk-11.0.1+13


2. Download jarfix

Download jarfix.exe from the jarfix homepage and store the .exe on a folder of your choice on your harddrive. On my Windows instance, I have stored the jarfix.exe to C:\Applications\jarfix\




3. Create a jarfix config file

Create a jarfix.ini file to C:\Applications\jarfix\ with the following content:

[jarfix]
options=/a
action="C:\Applications\jdk-11.0.1+13\bin\javaw.exe" -jar  "%1" %*


Those entries tell jarfix to setup a .jar association with the OpenJDK in C:\Applications\jdk-11.0.1+13\ - you may want to modify that path according to the actual path that you have choosen at step 1. The line called "options=/a" is optional, it tells jarfix to create a "Open as Administrator" menu entry in order to run .jar files also under the Admin account.

Hint: you can run jarfix /x in order to extract an example jarfix.ini file which has a lot of useful examples for a Java developer on Windows.

Update January 27, 2019: from Jarfix version 3 you can recreate hijacked .jar associations out of the box (by a double click without an .ini file) not only for the Oracle JDK, but also for the OpenJDK from Azul Systems.



4. Run jarfix using the config file

Open a Windows Command Prompt or simply hit both the Windows Key and R in order to enter the following command:

C:\Applications\jarfix\jarfix.exe /c

Update January 27, 2019: from Jarfix version 3 it is not necessary anymore to pass the option /c as a parameter. If a .ini file exists with the same name as the .exe in the same directory, jarfix will read the .ini file in order to initialize itself with the values from the .ini. In other words, you can simply double click on jarfix.exe and the content of jarfix.ini will be taken into account.








5. Test it

If you have run "jarfix /x" at step 3, you can double click on the existing jartest.jar in C:\Applications\jarfix in order to test whether it works as expected:

As you can see above we have launched the OpenJDK from AdoptOpenJDK by double-clicking on a .jar file.

How to install or update your preferred JDK with one single command on macOS or GNU/Linux?

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macOS: To use the java command-line tool you need to install a JDK - are you kidding me?

Recently I detected an error message on macOS saying that it seems to be required to install a JDK in order to just use the java command-line tool. A JRE is not enough? Really? Are you kidding me?

The screenshot below shows the error message in German: "Um das java-Befehlszeilenprogramm nutzen zu können, musst du ein Java-Entwicklerpaket installieren." In English it means: "To use the java command-line tool you need to install a JDK".

Since I am a developer, I always installed the JDK on my Mac and I detected that phenomenon very late. Actually the web is full of those traces - however, without a suitable solution in my opinion. Well, I simply don't want to tell my users to install a JDK if a simple JRE is enough. Any existing JRE on the system should do the job in my humble opinion.

Here we go, here is my little bash launcher that tries its best to launch java even if you have installed a JRE only on your Mac:

#!/bin/bash

if [[ ! -z $JAVA_HOME ]]; then

    JEXEC=$JAVA_HOME/bin/java

else

    LIBEXEC=$(/usr/libexec/java_home 2> /dev/null | head -1)

    # is there a JDK?

    if [[ ! -z $LIBEXEC ]]; then

        JEXEC="$LIBEXEC/bin/java"

    else

       # is there a JRE?

       JRE=/Library/Internet\ Plug-Ins/JavaAppletPlugin.plugin/Contents/Home/bin/java

       if [[ -f "$JRE" ]]; then

           JEXEC="$JRE"

       else

           JEXEC=java

       fi

    fi

fi

"$JEXEC" "$@"

The script checks for the JAVA_HOME environment variable and if that is not set, it checks for any registered JDKs by calling /usr/libexec/java_home and if that didn't return anything, it simply uses the JRE that could be available at a well known path on macOS (tested with both Java 8u131 and Java 9-ea) and if that fails as well, it uses java and if even that fails it means you really don't have any Java installed and you should get the error message above again.

I use the launcher above already as part of the Jacksum macOS Finder integration. See also
http://jacksum.net/de/tutorials/integration_jacksum_osx_finder.html

Feel free to use the launcher script for your Java app as well if it meets your needs.