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JavaActionsComposition
This chapter introduces several ways to define generic action functionality.
Previously, we said that an action is a Java method that returns 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 builds a root action for you that just calls the proper action method. This allows for more complicated action composition.
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 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 several actions by using custom action annotations:
@Authenticated
@Cached(key="index.result")
public static Result index() {
return ok("It works!");
}
Note:
play.mvc.Security.Authenticated
andplay.cache.Cached
annotations and the corresponding predefined Actions are shipped with Play. See the relevant API documentation for more information.
You can also mark action composition with your own annotation, which must itself be annotated 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 retrieves the annotation as configuration:
public class VerboseAction extends Action<Verbose> {
public Result call(Http.Context ctx) {
if(configuration.value) {
Logger.info("Calling action for " + ctx);
}
return delegate.call(ctx);
}
}
You can also put any action composition annotation directly on the Controller
class. In this case it will be applied to all action methods defined by this controller.
@Authenticated
public Admin extends Controller {
…
}
You can pass an object from an action to a controller by utilizing the context args map.
public class SecurityAction extends Action<Verbose> {
public Result call(Http.Context ctx) {
ctx.args.put("user", User.findById(1234));
}
}
Next: Content negotiation
- Actions, Controllers and Results
- HTTP routing
- Manipulating the HTTP response
- Session and Flash scopes
- Body parsers
- Actions composition
- Content negotiation
- HTTP programming
- Asynchronous HTTP programming
- The template engine
- HTTP form submission and validation
- Working with JSON
- Working with XML
- Handling file upload
- Accessing an SQL database
- Using the Cache
- Calling WebServices
- Integrating with Akka
- Internationalization
- The application Global object
- Testing your application