Task parameters

Tasks don't just automatically accept parameters from external sources. That is, you need to take extra measures in order to make your tasks parameterizable from build scripts. In order to support this, the build system defines the ParameterizableTask extension interface.

public Task<? extends Void> createTask(ExecutionContext executioncontext) {
	return new ParameterizableTask<Void>() {
		private Object parameter;

		@Override
		public Void run(TaskContext taskcontext) throws Exception {
			taskcontext.println(Objects.toString(parameter));
			return null;
		}

		@Override
		public void initParameters(TaskContext taskcontext,
				NavigableMap<String, ? extends TaskIdentifier> parameters)
						throws TaskParameterException {
			parameter = taskcontext.getTaskResult(parameters.get("Parameter"));
		}
	};
}

In the above, instead of creating a task instance of Task, we create an instance of ParameterizableTask. The ParameterizableTask interface contains the interface method initParameters which is called by the build system before run(TaskContext). It is an initialization method that allows the task object to retrieve and assign the parameters of the task.

Running the above example in the following way:

example.task(Parameter: "Hello world!")

Will print out "Hello world!" accordingly.

The parameters are available through the Map argument which contains all the named parameters that were given to the task invocation. Each String key maps to the identifier of a task that provides the value of the given parameter. You can use the task context to retrieve the results for the given parameter task identifier, or handle the identifier in any other ways.

ParameterizableTask comes with a default implementation that assign the annotated field parameters of a task objects based on their annotations. See Parameter parsing for more information about it. Using the default mechanism, the above is roughly equivalent to the following:

return new ParameterizableTask<Void>() {
	@SakerInput(value = "Parameter", required = true)
	public String parameter;

	@Override
	public Void run(TaskContext taskcontext) throws Exception {
		taskcontext.println(parameter);
		return null;
	}
};

In which case the Parameter will be automatically assigned and converted to the String parameter field when the default implementation of initParameters is called.