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How to make a JAR file Linux executable

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Every Java programmer knows - or should known - that it is possible to create a runnable Java package archive (JAR), so that in order to launch an application it is enough to specify the jar file name on the Java interpreter command line along with the -jar parameter. For example:

$ java -jar helloworld.jar

There are plenty of tutorials showing how to implement this feature using Ant, Maven, Eclipse, Netbens, etc.

Anyway in its basic form, it just requires to add a MANIFEST.MF file to the jar package. The manifest must contain an entry Main-Class that specifies which is the class defining the main method for your application. For example:

$ javac HelloWorld.java
$ echo Main-Class: HelloWorld > MANIFEST.MF
$ jar -cvmf MANIFEST.MF helloworld.jar HelloWorld.class 

But this still requires your users to invoke the Java interpreter with the -jar option. There are many reasons why it would be preferable to have your app runnable by simply invoking it on the terminal shell like any other command.

Here comes the protip!

This technique it is based on the ability to append a generic binary payload to a Linux shell script. Read more about this here: http://www.linuxjournal.com/content/add-binary-payload-your-shell-scripts

Taking advantage of this possibility the trick is just to embed a runnable jar file into a Bash script file. The script when executed will launch the Java interpreter specifying itself as the jar to run. Too complex? Much more easier to do in practice, than to explain!

Let's say that you have a runnable jar named helloworld.jar

Copy the Bash script below to a file named stub.sh

#!/bin/sh
MYSELF=`which "$0" 2>/dev/null`
[ $? -gt 0 -a -f "$0" ] && MYSELF="./$0"
java=java
if test -n "$JAVA_HOME"; then
    java="$JAVA_HOME/bin/java"
fi
exec "$java" $java_args -jar $MYSELF "$@"
exit 1 

Than append the jar file to the saved script and grant the execute permission to the file resulting with the following command:

cat stub.sh helloworld.jar > hello.run && chmod +x helloworld.run 

That's all!

Now you can execute the app just typing helloworld.run on your shell terminal.

The script is smart enough to pass any command line parameters to the Java application transparently. Cool! Isn't it ?!

In the case your are a Windows guy, obviously this will not work (except you will run a Linux compatibility layer like Cygwin).

Anyway exist tools that are able to wrap a Java application into a native Windows .exe binary file, producing a result similar to the one explained in this tutorial. See for example http://launch4j.sourceforge.net/

Comments

  • Blank-mugshot
    md2perpe

    During reading this article I got a feeling - rather than a clear memory - that I sometime, more than ten years ago, had seen a way to make Linux itself recognize files as executable.

    Here you can see how to do: http://www.kernel.org/doc/Documentation/binfmt_misc.txt Specific for Java: http://www.kernel.org/doc/Documentation/java.txt

  • Photo3
    athieriot

    That's amazing!

  • 0_ol4nobhp6vr3ga52y9z5oz5gozlaxsx2pz2doq61zpao8d1utbhskntjx45apelh0tveapzaia7j
    paolodt

    @md2perpe I known about Linux support for custom binary format, but for many users it cannot be an option because they may not have root permissions. So the above script is the best solution, if you need a transparent runnable Java app!

  • Blank-mugshot
    dongli

    This is just what I need! Thank you!

  • Blank-mugshot
    dongli

    @paolodt I encounter a problem when I use dynamic compilation in my JAR. The JAR will read in external Java sources that implement an interface in the JAR. When in Eclipse IDE, things work fine, but after creating the final executable file, it will fail with error "cannot read zip file entry". So there is any solution for this problem?

  • 0_ol4nobhp6vr3ga52y9z5oz5gozlaxsx2pz2doq61zpao8d1utbhskntjx45apelh0tveapzaia7j
    paolodt

    Hi, but what if you try to launch it using "java -jar "? Does it work or it fails

  • 0_ffbqyioxgnsqwu_s5ekjywmfhkojiugslhpjywmr0podq0zdwdberdvza4e6eyit625zlaryf9wr
    hduchesn

    I have an issue with your script and my jar :). my java apps is a GUI launcher in charge to start another program. When I launch the .run from terminal it works fine (I mean, I keep my env). But when I double click the .run, the GUI launcher appears but I lost my env and the start of other program failed because JAVA_HOME is not set... How to keep my env when I double click the .run?

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