Gradle task for Java playground

Question

I am still new to Docker and Gradle, but I am trying to setup a Gradle build that builds a Docker image.

I just finished setting up a Dockerfile which locally deploys and runs the jar as expected. I have this in my build.gradle:

buildscript {
    repositories {
        mavenCentral()
    }

    dependencies {
        classpath 'se.transmode.gradle:gradle-docker:1.2'
    }
}

plugins {
    id 'com.github.johnrengelman.shadow' version '1.2.3'
}

apply plugin: 'docker'

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


task buildDocker(type: Docker, dependsOn: shadowJar) {
    push = false

    applicationName = jar.baseName

    tagVersion = 'latest'
    dockerfile = file('src/main/docker/Dockerfile')

    copy {
        from shadowJar
        into stageDir
    }
}

I run ./gradlew build buildDocker to build the image. I am happy with this so far.

Usually I create a throwaway class (e.g. Playground.java) with a main method that I can run and disregard. Usually I just run this in the IDE, but now I would like to be able to connect to the other Docker containers that I know will be running.

I know I could try changing the sourceSets I'm using by excluding com.myapp.Main, but I was imagining there might be a more elegant solution resembling this:

task buildDockerPlayground(type: Docker, dependsOn: shadowJar) {
    main = 'com.myapp.Playground'

    push = false

    applicationName = jar.baseName

    tagVersion = 'latest'
    dockerfile = file('src/main/docker/Dockerfile')

    copy {
        from shadowJar
        into stageDir
    }
}

Another approach might be to have another task that I use to replace build when I call ./gradlew build buildDocker, e.g. ./gradlew playground buildDocker. Is this more practical?

Answer 1

I would suggest replacing your hard coded main class with a gradle project property.

jar {
    manifest {
        attributes 'Main-Class': main
    }
}

Set that default property in your gradle.properties file.

main=com.myapp.Main

Finally, when you need to build your docker container that uses a jar running com.myapp.Playground you can invoke gradle with:

./gradlew buildDocker -Pmain=com.myapp.Playground

Edit: To achieve the same thing in a task

project.ext.main = 'com.myapp.Main'

task play(){
    project.main = 'com.myapp.Playground'
    finalizedBy buildDocker
}

jar {
    manifest {
        attributes 'Main-Class': project.main
    }
}