How do I specify default values for gradle custom Java task inputs?

Question

I've got a custom Gradle task written in Java as part of a Gradle plugin that look like this:

public abstract class MyTask extends DefaultTask {

    private static final String DEFAULT_SERVICE_VERSION = "NO VERSION";
    private String serviceVersion;

    @Option(option = "serviceVersion", description = "Configures the service version.")
    public void setServiceVersion(String serviceVersion) {
        this.serviceVersion = serviceVersion;
    }

    @Input
    public String getServiceVersion() {
        return serviceVersion;
    }


    @TaskAction
    public void myTask() {
        String serviceVersionCurrent = getServiceVersion() != null ? getServiceVersion() : DEFAULT_SERVICE_VERSION;

This allows me to call the task with serviceVersion as parameter as follows:

gradle myTask --serviceVersion="0.1"

I would like to make serviceVersion somehow optional and if no value is specified, then default to DEFAULT_SERVICE_VERSION

As it is now, it fails:

> gradle myTask
> Task :myTask FAILED

FAILURE: Build failed with an exception.

* What went wrong:
Some problems were found with the configuration of task ':myTask' (type 'MyTask').
> No value has been specified for property 'serviceVersion'.

How should I annotate my property to make it default to a certain value if none is specified?

Answer 1

Just assign the default value at the variable initialization:

public class GreetingTask extends DefaultTask {
  private String serviceVersion = "v1.0";

  @Option(option = "serviceVersion", description = "Configure service version")
  public void setServiceVersion(String serviceVersion) {
    this.serviceVersion = serviceVersion;
  }

  @Input
  public String getServiceVersion() {
    return this.serviceVersion;
  }

  @TaskAction
  public void task() {
    System.out.println(this.serviceVersion);
  }
}

The output would be:

$ ./gradlew greeting

> Task :greeting
v1.0

BUILD SUCCESSFUL in 2s
3 actionable tasks: 3 executed

$ ./gradlew greeting --serviceVersion=v2.0

> Task :greeting
v2.0

BUILD SUCCESSFUL in 1s
3 actionable tasks: 1 executed, 2 up-to-date