Custom Gradle Plugin configuration resolution time

Help/Discuss
1

Hello,

I’m working on building a custom gradle plugin that cobbles a bunch of my favorite other plugins together for a micro service framework I own. Right now I’m trying to customize the ApplicationPlugin with a customStartScript.

In the service using my plugin I have something that looks like this:

plugins {
     id "com.plugin"
}

service {
    mainClass = "com.thing.MainClass"
}

In my custom plugin I have code that looks like this:

project.getTasks().register(CUSTOM_START_SCRIPT_TASK_NAME, CreateStartScripts.class, (task)->{
       ServiceConfiguration service = (ServiceConfiguration) project.getExtensions().getByName("service");
       task.setMainClassName(service.mainClass);
}

The issue is that service.mainClass is null when I debug. I’m assuming that if I could set the mainclass on the JavaApplicationPlugin convention that might do the work for me, but I can’t work out how wire up the providers to do that.

Any advice here would be greatly appreciated.

2

Assuming service.mainClass is a Property<String>, then your plugin can establish a default value by linking the application.mainClass and service.mainClass properties using:

YourServiceExtension sE = project.getExtensions().create("service", YourServiceExtension.class);
project.getExtensions().getByType(JavaApplication.class)
                                         .getMainClass().convention(sE.getMainClass());
1 Like
3

This is definitely the type of direction I was looking for. My ServiceConfiguration is a bean, I’m not really sure how to wire up the Property correctly.

I have something like this:

import org.gradle.api.provider.Property;
public class ServiceConfiguration {
       public Property<String> mainClass;
}

But when I try to register the extension the value is null.

class ServicePlugin implements Plugin<Project> { 
     @Override
     public void apply(Project project) {
           ServiceConfiguration serviceConfiguration = project.getExtensions().create("service", ServiceConfiguration.class);
           project.getExtensions().getByType(JavaApplication.class).getMainClass().convention(serviceConfiguration.mainClass);
     }    
}

I’m clearly missing a step here. This is how I’m registering the plugin.

plugins {
    `kotlin-dsl`
    `java-gradle-plugin`
}
gradlePlugin {
    plugins {
        create("service") {
            id = "com.plugin"
            implementationClass = "com.plugin.ServicePlugin"
        }
    }
}

I’ve seen examples of creating the properties for custom tasks, but that’s not really what I’m trying to do here, so I’m not totally sure what to do.

4

Your plugin is not creating an instance of Property<String> and assigning it to mainClass. There’s a few ways you could do this, but my recommendation is that you take advantage of Gradle’s “managed properties”. To do this change your ServiceConfiguration class to:

public abstract class ServiceConfiguration {
    public abstract Property<String> getMainClass();
}

When you then use this type for creating your extension, Gradle will generate a concrete class with the necessary implementation. You then pass convention the result of getMainClass(). Note, you do not need a setter, the property should be “final” and builds will change the value stored in the property instance, not change the property reference in the extension.

See also, Developing Custom Gradle Types

5

This is super awesome. Thank you so much for your help!!!