无法找到或加载主类

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最佳答案

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

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']
```
mainClassName should be fully qualified class name, not path.
```
mainClassName = "hello.HelloWorld"
```

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I just ran into this problem and decided to debug it myself since i couldn't find a solution on the internet. All i did is change the mainClassName to it's whole path(with the correct subdirectories in the project ofc)

    mainClassName = 'main.java.hello.HelloWorld'

I know it's been almost one year since the post has been made, but i think someone will find this information useful.

Happy coding.

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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'
}
}

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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.

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In my build.gradle, I resolved this issue by creating a task and then specifying the "mainClassName" as follows:

task(runSimpleXYZProgram, group: 'algorithms', description: 'Description of what your program does', dependsOn: 'classes', type: JavaExec) {
mainClassName = 'your.entire.package.classContainingYourMainMethod'
}

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Just to make it clear for newbies trying to run a gradle project from Netbeans:
To understand this, you need to see what the main class name looks like and what the gradle build looks like:

Main class:

package com.stormtrident;


public class StormTrident {
public static void main(String[] cmdArgs) {
}
}

Notice that it is part of the package "com.stormtrident".

Gradle build:

apply plugin: 'java'


defaultTasks 'jar'


jar {
from {
(configurations.runtime).collect {
it.isDirectory() ? it : zipTree(it)
}
}
manifest {
attributes 'Main-Class': 'com.stormtrident.StormTrident'
}
}




sourceCompatibility = '1.8'
[compileJava, compileTestJava]*.options*.encoding = 'UTF-8'


if (!hasProperty('mainClass')) {
ext.mainClass = 'com.stormtrident.StormTrident'
}


repositories {
mavenCentral()
}


dependencies {
//---apache storm
compile 'org.apache.storm:storm-core:1.0.0'  //compile
testCompile group: 'junit', name: 'junit', version: '4.10'
}

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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

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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.

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verify if gradle.properties define right one JAVA_HOVE

org.gradle.java.home=C:\Program Files (x86)\Java\jdk1.8.0_181

or

if it's not defined be sure if Eclipse know JDK and not JRE

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I resolved it by adding below code to my application.

// enter code here this is error I was getting when I run build.gradle. main class name has not been configured and it could not be resolved

public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}

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If you decided to write your hello.World class in Kotlin, another issue might be that you have to reference it as mainClassName = "hello.WorldKt".

src/main/java/hello/World.kt:

package hello
fun main(args: Array<String>) {
...
}
// class World {} // this line is not necessary

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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'

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For Netbeans 11 users, this works for me:

apply plugin: 'java'
apply plugin: 'application'


// This comes out to package + '.' + mainClassName
mainClassName = 'com.hello.JavaApplication1'

Here generally is my tree:

C:\...\NETBEANSPROJECTS\JAVAAPPLICATION1
│   build.gradle
├───src
│   ├───main
│   │   └───java
│   │       └───com
│   │           └───hello
│   │                   JavaApplication1.java
│   │
│   └───test
│       └───java
└───test

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If you're using Spring Boot, this might be the issue: https://github.com/gradle/gradle/issues/2489.

Basically, the output directories changed in Gradle 4.0, so if you have them hardcoded the execution will fail.

The solution is to replace:

bootRun {
dependsOn pathingJar
doFirst {
classpath = files("$buildDir/classes/main", "$buildDir/resources/main", pathingJar.archivePath)
}
}

by:

bootRun {
dependsOn pathingJar
doFirst {
classpath = files(sourceSets.main.output.files, pathingJar.archivePath)
}
}

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I had forgotten to add String[] args inside main method public static void main()

After changing it to public static void main(String[] args), everything worked.

My build.gradle looks like this

apply plugin: 'java'
apply plugin: 'application'
mainClassName = 'hugo.HelloWorld'

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For Kotlin DSL (build.gradle.kts) use this code:

tasks.jar {
manifest.attributes["Main-Class"] = "my.package.name.MyClassName"
// ...
}

Another similar notation:

tasks.jar {
manifest {
attributes["Main-Class"] = "my.package.name.MyClassName"
}
// ...
}