How do I run a main method in a Java Gradle project from command line?

Question

I have a Gradle project (say, MyProject ) that has a main method that I only want to use to run a small Java app. Say, the script is in a class and package as follows:

package com.car.ant;

import com.3rdparty.library.LibraryException;

public class MyScript {
    public static void main(String[] args) {
        System.out.println("Hello world!");
    }
}

I build the project with $ ./gradlew clean build , no problem. I am trying to run this via command line, but when I do, I get an Exception when trying to run:

$ pwd
~/workspace/MyProject/build/classes/java/main
$ java com.car.ant.MyScript
Exception in thread "main" java.lang.NoClassDefFoundError: com/3rdparty/library/exception/LibraryException
        at java.lang.Class.getDeclaredMethods0(Native Method)
        at java.lang.Class.privateGetDeclaredMethods(Class.java:2701)
        at java.lang.Class.privateGetMethodRecursive(Class.java:3048)
        ... 7 more

This script is not the main part of the app, but I just want it in there to run every once in a while, and I'd like to figure out how to run it by itself command line. Is there a way to do this without importing anymore libraries? I've seen this done with one-jar, but I thought I could do this without one-jar.

Tried to add a classpath after reading this , but now I'm getting a different error:

$ java -cp com/3rdparty/library/exception/LibraryException com.car.ant.MyScript
Error: Could not find or load main class com.car.ant.MyScript

Answer 1

You can read about how to do this at the Gradle Docs .

apply plugin: 'application'
mainClassName = "com.mycompany.myapplication.MyScript"
applicationDefaultJvmArgs = [
    "-Djava.util.logging.config.file=src/main/resources/logging.properties"
]

Then simply use gradlew run to run your application.

As an added benefit, this plugin helps you to package your app for distribution. Use the gradle distZip command for that.

Answer 2

Try this.

    plugins {
    id 'java-library'
    id 'application'
}
sourceCompatibility = JavaVersion.VERSION_1_8
targetCompatibility = JavaVersion.VERSION_1_8
/*
sourceCompatibility is "Java version compatibility to use when compiling Java source." 
targetCompatibility is "Java version to generate classes for."
*/
repositories {
    jcenter()
}
dependencies {
}


//To run the class name from command line using gradle run
mainClassName = 'com.sam.home.HelloWorld'

//To create a runnable jar  in GradleJavaProject\build\libs then java -jar GradleJavaProject.jar
jar {
    manifest {
        attributes 'Main-Class': 'com.sam.home.HelloWorld'
    }
}
//Beyond this line evertyhing is optional
//Alternatively you can run it as a task too gradle -q  runWithJavaExec
task runWithJavaExec(type: JavaExec) {
    group = "Execution"
    description = "Run the main class with JavaExecTask"
    classpath = sourceSets.main.runtimeClasspath
    main = 'com.sam.home.HelloWorld'
}
wrapper {
gradleVersion = '5.5'
distributionType = Wrapper.DistributionType.BIN
}

In command line type either gradle run or gradle -q runWithJavaExec