“Could not find main method from given launch configuration” error when exporting jar from Eclipse

Question

I developed my program using Eclipse as my IDE. I used to use File|Export| Runnable JAR file File|Export| Runnable JAR file option for creating dist build for client.

I was working with project using Run or (often) Debug button in eclipse (so I have configuration for project with valid main method).

Unfortunately when I created build yesterday I had following error when I tried to run app:

Failed to load Main-Class manifest attribute from My.jar

Then when I retried exporting I found the following problem in export log:

Could not find main method from given launch configuration

I have no idea what could cause this problem. I think I hadn't change anything in my project configuration. And I'm test my builds so I'm sure this option used to work correctly.

I will appreciate any help.

Answer 1

Are you selecting correct 'Launch Configuration' in the export dialog? Make sure it's from your project.

Also, once exported you could unzip jar file and look into 'META-INF/MANIFEST.MF' file - there should be 'Main-Class' entry with fully qualified name of your class where the main() method is.

Answer 2

I had this problem and none of the other options worked. Even removing and starting with a new workspace. In my case the problem was that I hadn't manually added the "classes" directory of my project to the classpath of the debug configuration that I was using to debug the java app. I don't know why it didn't pick up the classes directory automatically as part of the project from which I was running the app. In any case it started working again after that.

Answer 3

just had the same problem :s it's annoying but easy to manually fix in the manifest file.

1. open the .jar file with winrar or 7zip.
2. locate the manifest file (META-INF folder)
3. change it to this.

Manifest-Version: 1.0 main-class: (package).(main-class)

In my case i had it in the default package.

Manifest-Version: 1.0 main-class: run