Iterative BI + Gradle Tips and Tricks: Building a Custom Plugin

To build a custom plugin in groovy, do this.  I know this seems redundant, but it wasn’t as clear as it should have been.

1. Create a project directory.  Just a plain ol’ directory. Wherever you like.

2. Add the source file subdirectories:

src\main\groovy\…  (with the package path you’d like to use.  We have src\main\groovy\com\perficient\gradle)

3. Create a plugin class (in a file named <classname>.groovy, we have DatabasePlugin.groovy here).

package com.perficient.gradle

import org.gradle.api.Project
import org.gradle.api.Plugin

class DatabasePlugin implements Plugin<Project> {
    void apply(Project project) {
        project.convention.plugins.database = new DatabaseConvention(project) // if you have a custom convention class. Omit if not.

        // Configure your tasks here.  Add as many as you need.
        project.task('build') {
            description = 'Configure the environment with the specific environment code/name.'
        }

        project.task('build') << { println "Add actions like this if needed." }

        // All the normal task configuration (dependsOn, Type) can go as the first param.
        project.task(dependsOn: 'build', 'test') {
            decription = 'Run tests after building the database.'
        }
    }
}

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4. Add a properties file in src\main\resources\META-INF\gradle-plugins with the name of your plugin.  We have Database.properties and AgileBiEnv.properties in here.  In these files add one line (modified as needed):

implementation-class=com.perficient.gradle.DatabasePlugin

5. Add a build.gradle file to the plugin root:

apply plugin: 'groovy'

dependencies {
    compile gradleApi()
    groovy localGroovy()
}

Once you start getting non-trivial, you may need to add external jars to the classpath (add this to build.gradle):

sourceSets {
    main {
        groovy {
            compileClasspath += fileTree(dir: '../../../tools/lib', includes:['*.jar'])
        }
    }
}

And, if you want the jar to end up somewhere specific:

jar {
    destinationDir = new File('../../lib')
}

6. Finally, add a settings.gradle file to the root to set the name of the jar you’ll create:

rootProject.name = 'AgileBi'

You’re all set! Run “gradle build” from the command line in the plugin root directory and you should have a shiny new plugin jar to use in your build.

OK, I have a jar. Now what?

Elsewhere in your system, you’ll have a place where you want to use your plugin.  In the build.gradle there, add this:

buildscript {
    dependencies {
        classpath fileTree(dir: '../system/build/lib', include: '*.jar')
    }
}

apply plugin: 'Database'

When you run “gradle tasks” from this directory, you should now see the tasks you created in your plugins Apply() function.