.jar file error "could not find or load main class" with IntelliJ

Question

This is my MainBot.java code:

public class MainBot {
    public static void main(String[] args) {
        new MainBot("my_private_token");
    }

    public MainBot(String token) {
        // do stuff
    }
}

I have the following problem: When I try to execute the .jar file generated by IntelliJ, I get the following error:

could not find or load main class: MainBot

But when I look in the .jar file using WinRAR, I see this:

The MainBot.class file is there! The manifest file in the META-INF/ folder looks like this:

Manifest-Version: 1.0
Main-Class: MainBot

And the the META-INF folder looks like this:

What did I do wrong? When exporting, I select the correct main file in INTELLIJ, add the META-INF directory to resources/ and then I build my artifact. How come that The MainBot file cannot be found, when it is there?! I also tried playing arond with the MAINFEST.MF file and tried changing the Main-Class to ../MainBot or something, but none of that worked.

EDIT: This is the artifact under Project Structure | Artifacts

May you share a sample project and artifact configuration under "Project structure | Artifacts"? — Konstantin Annikov, Oct 25 '21 at 05:35
Given the presence of a module-info.class, you're using a modular project, then you shouldn't use the default package. Put `MainBot` in a package. — Mark Rotteveel, Oct 27 '21 at 12:54
@MarkRotteveel I did that, now is says that the main class cannot be found at `package.MainBot`. — Lars, Oct 28 '21 at 14:31
Can you share MainBot code? Or at least class declaration and main method declaration? — msl, Oct 28 '21 at 18:00
Did you check this? https://stackoverflow.com/a/21650867/9391162 — AMK, Oct 28 '21 at 18:11
@AMK that did sadly not work, as I have my MainBot.class in a package called entry. — Lars, Oct 29 '21 at 08:38
It's in a package called entry? Not in the code examples and screenshots you have posted. — Robert Mikes, Oct 29 '21 at 15:40

score 3 · Accepted Answer · answered Oct 30 '21 at 04:53

The META-INF folder in your generated Jar has these 2 files -

SIGNINGGC.RSA
SIGNINGGC.SF

I assume that you are not signing the Jar. Then, these files must be coming from one of your dependancies when you are creating a Fat Jar. If any of your dependancies has a Signed Jar, then it could result into that could not find or load main class: exception.

You can quickly find if this is the issue by removing those files with this command (referenced from here) and try and run the code -

zip -d yourjar.jar 'META-INF/*.SF' 'META-INF/*.RSA' 'META-INF/*.DSA'

IntelliJ shows 2 Options while generating Jar. The first one will generate a Fat Jar. The other option will keep the other library jars intact and link with them using Manifest file.

Assuming all you need is to run your code, use the second option in the Create Jar from Modules Dialog box.

I cannot thank you enough! Sadly, the zip command did not work, but manually deleting the files with WinRar did! — Lars, Nov 01 '21 at 21:14

score 1 · Answer 2 · answered Oct 29 '21 at 22:56

I attempted to reproduce the error using a sample application that uses gradle, following this tutorial, but I couldn't. The sample application has a module named io.github.devatherock.example, which holds the module-info.java file and a package named io.github.devatherock.example, which contains the main class MainBot.java. I have listed the main class as io.github.devatherock.example.MainBot in gradle which produces a jar file with below manifest:

Manifest-Version: 1.0
Main-Class: io.github.devatherock.example.MainBot

The jar executes without any error. In the IDE, the structure of the source code looks like below:

garawaa garawaa · Answer 3 · 2022-08-25T09:56:41.363

0

In Windows after generating jar file, in generated folder run command

7z d yourjar.jar META-INF/*.SF META-INF/*.RSA META-INF/*.DSA -r

you must installed 7zip and added enviorment path

edited Aug 25 '22 at 09:56

answered Aug 25 '22 at 08:18

garawaa garawaa

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.jar file error "could not find or load main class" with IntelliJ

3 Answers3