JavaActionsComposition

Actions composition

This chapter introduce several ways of defining generic functionalities for actions.

Reminder about actions

Previously we said that an action was a Java method returning a play.mvc.Result value. Actually, Play manages internally actions as functions. Because Java doesn't support first class functions, an action provided by the Java API is an instance of play.mvc.Action:

public abstract class Action {
    
  public abstract Result call(Http.Context ctx);    
    
}

Play build a root action for you which is just calling the proper action method. It allows for more complicated action composition.

Composing actions

You can compose the code provided by the action method with another play.mvc.Action, using the @With annotation:

@With(VerboseAction.class)
public static Result index() {
  return ok("It works!");
}

Here is the definition of the VerboseAction:

public static class VerboseAction extends Action.Simple {

  public Result call(Http.Context ctx) throws Throwable {
    Logger.info("Calling action for " + ctx);
    return delegate.call(ctx);
  }

}

At one point you need to delegate to the wrapped action using delegate.call(...).

You also mix with several actions:

@With(Secured.class, Cached.class)
public static Result index() {
  return ok("It works!");
}

Defining custom action annotations

You can also mark action composition with your own annotation, that you need to annotate itself using @With:

@With(VerboseAction.class)
@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
public @interface Verbose {
   boolean value() default true;
}

You can then use your new annotation with an action method:

@Verbose(false)
public static Result index() {
  return ok("It works!");
}

Your Action definition retrieve the annotation as configuration:

public static class VerboseAction extends Action<Verbose> {

  public Result call(Http.Context ctx) {
    if(configuration.value) {
      Logger.info("Calling action for " + ctx);  
    }
    return delegate.call(ctx);
  }

}

Annotating controllers

You can also put any action composition annotation directly on the Controller class. In this case it will be applied to all actions methods defined by this controller.

@Secured
public Admin extends Controller {
    
  ...
    
}

Next: Asynchronous HTTP programming