Issue
Okay so basically, every time I've seen this question asked it doesn't have the answer I'm looking for which is why I'm trying to ask myself.
Basically, I made a java project on BlueJ (required by school, sadly. But I can export it elsewhere if that's the problem (preferably IntelliJ or Visual Studio Code)), but essentially, I want to make it so I can simply double click my .jar export and it will open a terminal window and launch. When I try this however, I get this error: First Error
And when I click Ok then this appears: Second Error
Now, if I want the jar to run on terminal, doing java -jar jarFileName.jar works perfect, but what I want is for that to happen when I double click the jar file; for it to launch and run from the terminal.
All the other answers I've seen for this problem blame the users computer and usually tell them to install some version of java or whatever, but this isn't the problem. I have other jar files that I can run perfectly fine, like Minecraft Forge installer or Minecraft Spigot installers (sorry only examples are Minecraft, not much else uses Java). And also this was for a uni project and no one else in my field know how to get their jar to be executable, nor does this file work for anyone else.
So yeah, I know it's a problem with how the jar was compiled or something and not what java is installed my PC.
I just want to make it double-clickable for the convenience of when I send it to friends, but if anyone knows another way I can get around this problem then that's fine. For example I know I could make a Bash file which simply does the java -jar jarFileName.jar for me or something, but I'd rather have it all as one jar file, so I don't know if this can be incorporated into the file but yeah.
Also I'd really like a solution which doesn't involve downloading external programs or whatever, since all I want to do is send this file to my friends and have them just double click it to launch.
TL;DR, what do I have to do to make my jar file actually executable by double clicking it. Thank you.
Solution
To make a jar file executable you have to set the entrypoint
You can do this by passing the e option to the jar command when you create the jar file, for example:
jar cvfe myapp.jar com.mycompany.myapp.MyApp com\mycompany\myapp
This will add the Main-Class entry in the jar's manifest pointing to the startup class, which should have a main method, for example:
package com.mycompany.myapp;
public class MyApp {
public static void main(String[] args) {
// start up the application
}
}
When you create a JAR file, it automatically receives a default manifest file. There can be only one manifest file in an archive, and it always has the pathname
META-INF/MANIFEST.MF
The entrypoint is specified by the Main-Class, for example:
Manifest-Version: 1.0
Created-By: 1.8.13_37 (Oracle Corporation)
Main-Class: com.mycompany.myapp.MyApp
If you want to make an existing jar file executable you could unzip it, modify the manifest and zip it again (and rename it so it has the .jar extension - a jar is just a zip).
But I think the errors you show are not caused by the jar not being executable, but by some environment issue, causing the Java application to not find the necessary variables or paths to make the Java Native Integration (JNI) work. To solve this you would have to provide more detail on what you are trying to do with JNI.
Answered By - Adriaan Koster
Answer Checked By - Dawn Plyler (JavaFixing Volunteer)
