Gradle - Could not find or load main class

Question

I\'m trying to run a very simple project using Gradle and running into the following error when using the gradlew run command:

could not find or l

Answer 1

For a project structure like

project_name/src/main/java/Main_File.class

in the file build.gradle, add the following line

mainClassName = 'Main_File'

Answer 2

I fixed this by running a clean of by gradle build (or delete the gradle build folder mannually)

This occurs if you move the main class to a new package and the old main class is still referenced in the claspath

Answer 3

Struggled with the same problem for some time. But after creating the directory structure src/main/java and putting the source(from the top of the package), it worked as expected.

The tutorial I tried with. After you execute gradle build, you will have to be able to find classes under build directory.

Answer 4

When I had this error, it was because I didn't have my class in a package. Put your HelloWorld.java file in a "package" folder. You may have to create a new package folder:

Right click on the hello folder and select "New" > "Package". Then give it a name (e.g: com.example) and move your HelloWorld.java class into the package.

Answer 5

Modify build.gradle to put your main class in the manifest:

jar {
    manifest {
        attributes 'Implementation-Title': 'Gradle Quickstart',
                   'Implementation-Version': version,
                   'Main-Class': 'hello.helloWorld'
    }
}

Answer 6

I see two problems here, one with sourceSet another with mainClassName.

1. Either move java source files to src/main/java instead of just src. Or set sourceSet properly by adding the following to build.gradle.

   sourceSets.main.java.srcDirs = ['src']
   

2. mainClassName should be fully qualified class name, not path.

   mainClassName = "hello.HelloWorld"