create executable jar with gradle

Question

I have a task to create xxxxx.jar executable file that mast be run with:

java xxx.jar

I have tried to do this with gradle by setting

jar {
    manifest {
        attributes 'Main-Class': 'com.Main'
    }
}

but once I run java xxxxx.jar I get:

Error: Could not find or load main class xxxxx.jar

I how ever i can run it with java -jar xxxxx.jar but I need to execute the file just with java xxxxx.jar

What can change to run it just with java xxxxx.jar. I suspect this might be some where in the gradle file.