org.apache.reef.tang

Interface Aspect

All Known Implementing Classes:

WakeProfiler

public interface Aspect

A simple interface that allows external code to interpose on Tang object injections. This can be used to implement simplistic aspect oriented design patterns by interposing wrapper objects at injection time. It can also be used for more mundane purposes, such as tracking the relationship between the objects that are instantiated at runtime.

The Wake project contains a full-featured implementation of this API that may serve as a useful example.

Method Summary

Methods

Modifier and Type	Method and Description
Aspect	createChildAspect() This method creates a child aspect, and returns it.
<T> T	inject(ConstructorDef<T> def, Constructor<T> constructor, Object[] args) Inject an object of type T.
<T> void	injectionFutureInstantiated(InjectionFuture<T> f, T t) TANG calls this the first time get() is called on an injection future.

Method Detail

inject

<T> T inject(ConstructorDef<T> def,
           Constructor<T> constructor,
           Object[] args)
         throws InvocationTargetException,
                IllegalAccessException,
                IllegalArgumentException,
                InstantiationException

Inject an object of type T.

Note that it is never OK to return an instance of ExternalConstructor. Typical implementations check to see if they are about to return an instance of ExternalConstructor. If so, they return ret.newInstance() instead.

Parameters:

def - information about the constructor to be invoked. This is mostly useful because it contains references to any relevant named parameters, and to the class to be injected.

constructor - The java constructor to be injected. Tang automatically chooses the appropriate constructor and ensures that we have permission to invoke it.

args - The parameters to be passed into constructor.newInstance(), in the correct order.

Returns:

A new instance of T. Note, it is inject()'s responsibility to call ret.getInstance() if ret instanceof ExternalConstructor.

Throws:

A - number of exceptions which are passed-through from the wrapped call to newInstance().

InvocationTargetException

IllegalAccessException

IllegalArgumentException

InstantiationException

injectionFutureInstantiated

<T> void injectionFutureInstantiated(InjectionFuture<T> f,
                                   T t)

TANG calls this the first time get() is called on an injection future. This informs the aspect of the relationship between InjectionFutures (that were already passed into inject()) and the instantiated object.

Parameters:

f - An InjectionFuture that was passed to the args[] array of inject at some point in the past.

t - An object instance that was returned by inject().

createChildAspect

Aspect createChildAspect()

This method creates a child aspect, and returns it. This allows aspects to track information about Tang injection scopes. If such information is not needed, it is legal for Aspect implementations to return "this".