Gradle application plugin with multiple main classes

Question

I'm using the gradle 'application' plugin to start my application. This works well. Now I want to add the option to start a different main class in the same project. Can I change the plugin's configuration to allow that?

apply plugin: 'application'

mainClassName = "net.worcade.my.MainClass"

What is the condition that you want to base this conditional config on? — Manish Kumar Sharma, May 12 '17 at 12:14
I'm open to suggestions. A command line parameter, a `-D` argument... — Jorn, May 12 '17 at 12:19
But there must be some condition in which you want this to be main class..what is that? — Manish Kumar Sharma, May 12 '17 at 12:20
In my IDE, I'd just make two run targets, one for each main class. So the first one could call `gradle run first` and the second one could call `gradle run second`. — Jorn, May 12 '17 at 12:23
If that's all you need, you can either run the class directly from the IDE, without going through gradle, or add two tasks of type JavaExec to your build file. https://docs.gradle.org/3.5/dsl/org.gradle.api.tasks.JavaExec.html — JB Nizet, May 12 '17 at 12:40

score 24 · Accepted Answer · answered Oct 25 '17 at 17:02

From http://mrhaki.blogspot.com/2010/09/gradle-goodness-run-java-application.html

apply plugin: 'java'

task(runSimple, dependsOn: 'classes', type: JavaExec) {
   main = 'com.mrhaki.java.Simple'
   classpath = sourceSets.main.runtimeClasspath
   args 'mrhaki'
   systemProperty 'simple.message', 'Hello '
}

Clearly then what you can change:

runSimple can be named whatever you want
set main as appropriate
clear out args and systemProperty if not needed

To run:

gradle runSimple

You can put as many of these as you like into your build.gradle file.

If you want to pass arguments from the command line you can do this with: `gradle runSimple --args 'arg1 arg2'` (You'll need to remove the `args` bit from the `task()` obviously) — Kevin Sadler, Mar 27 '19 at 21:04

score 8 · Answer 2 · answered Dec 06 '20 at 08:28

You can directly configure the Application Plugin with properties:

application {
    mainClassName = project.findProperty("chooseMain").toString()
}

And after in command line you can pass the name of the main class:

./gradlew run -PchooseMain=net.worcade.my.MainClass

score 4 · Answer 3 · answered May 28 '20 at 16:04

Here's how you can generate multiple start scripts if you need to package your apps

application {
    applicationName = "myapp"
    mainClassName = "my.Main1"
}
tasks.named<CreateStartScripts>("startScripts") {
    applicationName = "myapp-main1"
}
val main2StartScripts by tasks.register("main2StartScripts", CreateStartScripts::class) {
    applicationName = "myapp-main2"
    outputDir = file("build/scripts") // By putting these scripts here, they will be picked up automatically by the installDist task
    mainClassName = "my.Main2"
    classpath = project.tasks.getAt(JavaPlugin.JAR_TASK_NAME).outputs.files.plus(project.configurations.getByName(JavaPlugin.RUNTIME_CLASSPATH_CONFIGURATION_NAME)) // I took this from ApplicationPlugin.java:129
}
tasks.named("installDist") {
    dependsOn(main2StartScripts)
}

I like this approach. What about re-using the classpath value that the application plugin has set for the standard `startScripts` task? I could do so by using `classpath = tasks.startScripts.get().classpath` and the same with `outdir`. And it is probably also possible to let `startScripts` depend on the custom task, right? Inspired by [this answer](https://stackoverflow.com/a/59724219/1804173). — bluenote10, Dec 15 '21 at 12:56

score 1 · Answer 4 · edited Apr 20 '23 at 08:46

1

Use javaExec task to handle it :

task run(type: JavaExec) {
    classpath = sourceSets.main.runtimeClasspath

    if (project.hasProperty('chooseMain')){
        if (chooseMain == 'Main1'){
            main = 'application.Main1'
        } else if (chooseMain == 'second'){
            main = 'application.Main2'
        }
    } else {
        println 'please pass the main name'
    }
}

And from the command line pass your option in that way :

gradle run -PchooseMain=first

edited Apr 20 '23 at 08:46

koppor

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answered Dec 30 '17 at 14:06

Daniel Taub

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`main` is deprecated. – koppor Apr 20 '23 at 08:45

Gradle application plugin with multiple main classes

4 Answers4

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