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The GEF4 Common component provides key concepts and infrastructure to be potentially used by all other GEF4 components. It is internally comprised out of a single Common module.
The Common module of GEF4 Common provides basic abstractions and related support classes within the following packages:
The Activate package provides a general abstraction for objects that maintain an active state ( IActivatable) as well as a support-class ( ActivatableSupport) that can be used as a delegate to simply implement IActivatable conferment to its contract.
An IActivatable
maintains an 'active' state and can be activated and deactivated. It is also an
IPropertyChangeNotifier to propagate changes to its 'active' state to registered
PropertyChangeListeners.
To enforce that implementers of
IActivatable properly follow the above outlined contract, ActivatableSupport
may be used. It does not formally implement the
IActivatable interface but provides implementations for all its methods and can thus be simply used as a delegate, as follows:
public class MyActivatable implements IActivatable { // create delegates private PropertyChangeSupport pcs = new PropertyChangeSupport(this); private ActivatableSupport acs = new ActivatableSupport(this, pcs); public void activate() { acs.activate(); } ... }
It needs to be provided with a PropertyChangeSupport, which will be used to notify listeners changes of the 'active' state. In case the IActivatable, by which it is used as a delegate, is also IAdaptable, it will ensure that all IActivatable adapters are properly activated/deactivated when the IActivatable is activated or deactivated (it will not activate/deactivate adapters when being registered; this is supported by AdaptableSupport).
The Adapt package provides a modernized interpretation of org.eclipse.core.runtime.IAdaptable, providing the following enhancements:
Besides the IAdaptable, IAdaptable.Bound, and AdapterKey abstractions that formalize the modernized adaptable pattern, the package also provides a supporting class ( AdaptableSupport) to implement IAdaptable in compliance with its contract, as well as a standalone implementation ( AdapterStore).
An IAdaptable
provides facilities to register adapters and to retrieve them via a combination of a type key (
java.lang.Class or
com.google.common.reflect.TypeToken) and an (optional)
java.lang.String role, which are combined in an AdapterKey
. Having the option to use a
com.google.common.reflect.TypeToken instead of a simple
java.lang.Class key, enables the type-safe retrieval of adapters with parameterized types. The combination with an additional (optional) role enables that multiple adapters of the same type may be registered at an IAdaptable
.
The 'traditional' getAdapter(Class<T>) method provided by the Eclipse Core Runtime org.eclipse.core.runtime.IAdaptable here is a mere convenience operation that will retrieve the single adapter registered with the respective java.lang.Class key and the default role (or the only adapter registered under the given java.lang.Class key, if there is only one adapter for that type key).
Before retrieving adapters from an IAdaptable
, they have to be registered. The registration again includes a role (while a 'default' role is used in case no role is provided) and might require additional information about the actual adapter type by means of a
com.google.common.reflect.TypeToken. The additional type information is required in case it cannot be inferred from the registered adapter instance itself (which is the case for parameterized types).
An adapter can thus now be registered and retrieved in various ways:
// register and retrieve adapter 'a' of raw type 'A' under 'default' role (type info not required) adaptable.setAdapter(a); A a = adaptable.getAdapter(A.class); // register and retrieve adapter 'a' of parameterized type 'A<T>' under 'default' role (type info required) adaptable.setAdapter(new TypeToken<A<T>>(){}, a); A<T> a = adaptable.getAdapter(new TypeToken<A<T>>(){}); // register and retrieve adapter 'a' of raw type 'A' under role 'a1' (type info not required) adaptable.setAdapter(a, "a1"); A a = adaptable.getAdapter(AdapterKey.get(A.class, "a1")); // register and retrieve adapter 'a' of parameterized type 'A<T>' under role 'a1' (type info required) adaptable.setAdapter(new TypeToken<A<T>>(){}, a, "a1"); A a = adaptable.getAdapter(AdapterKey.get(new TypeToken<A<T>>(){}, "a1"));
To formalize support for notifying listeners about registration and unregistration of adapters, IAdaptable
furthermore extends
IPropertyChangeNotifier, which provides capabilities for registering and unregistering respective listeners.
To formalize that an adapter may need to obtain a back reference to an
IAdaptable, the IAdaptable.Bound
interface was introduced. If an adapter implements this interface, the adaptable at which the adapter is registered is responsible of providing a back reference to the adapter as follows:
public class MyAdaptable implements IAdaptable { public <T> void setAdapter(T adapter) { ... if (adapter instanceof IAdaptable.Bound) { ((IAdaptable.Bound<A>) adapter).setAdaptable(this); ... } public <T> void unsetAdapter(T adapter) { ... if (adapter instanceof IAdaptable.Bound) { ((IAdaptable.Bound<A>) adapter).setAdaptable(null); } ... } ... }
To enforce that implementers of
IAdaptable properly follow the above outlined contract, AdaptableSupport
may be used. It does not formally implement the
IAdaptable interface but provides implementations for all its methods and can thus be simply used as a delegate, as follows:
public class MyAdaptable implements IAdaptable { // create delegates private PropertyChangeSupport pcs = new PropertyChangeSupport(this); private AdaptableSupport<MyAdaptable> ads = new AdaptableSupport<MyAdaptable>(this, pcs); public <T> T getAdapter(AdapterKey<T> key){ return ads.getAdapter(key); } ... }
It needs to be provided with a PropertyChangeSupport, which will be used to notify listeners about registration and unregistration of adapters. In case the IAdaptable, by which it is used as a delegate, is also IActivatable, it will ensure that all IActivatable adapters are properly activated/deactivated when being registered/unregistered dependent on the active state of the adaptable at that moment (it will not activate/deactivate adapters when the adaptable is activated or deactivated; this is supported by ActivatableSupport).
An AdaptableStore
is an
IAdaptable implementation that can be used standalone.
The Dispose package provides an abstraction ( IDisposable) for objects that need to be notified when being disposed.
An IDisposable
needs to be disposed. While the IDisposable
encapsulates the necessary steps that have to be performed when being disposed, the initiation of the disposal is left to its clients.
The Inject package contains Google Guice-based support for injecting adapters into an IAdaptable. That is, if an IAdaptable implementation provides an @InjectAdapters annotation on its <T> setAdapter(TypeToken<T>, T, String) method, and if corresponding adapter (map) bindings qualified with an @AdapterMap annotation are provided within a com.google.inject.Module, adapter instances can automatically be injected into instances of the IAdaptable. It needs to be pointed out that respective adapter (map) bindings are evaluated polymorphically, i.e. a concrete adaptable will also be injected with all adapters that registered for super types of it.
In addition to basic injection support for adapters, the package also provides support for scoping all objects that are injected in the (transitive) context of an IAdaptable by means of a dedicated com.google.inject.Scope ( AdaptableScope).
To enable injection of adapters to an
IAdaptable, a specific
com.google.inject.spi.TypeListener (AdaptableTypeListener
) needs to be registered in the
com.google.inject.Module. To ensure this is done properly, a respective support
com.google.inject.Module is provided, namely AdapterInjectionSupport
, which can easily be integrated into a custom
com.google.inject.Module as follows:
public class MyModule extends AbstractModule { @Override protected void configure() { // register adapter map injection support install(new AdapterInjectionSupport()); ... } }
This will ensure that the AdaptableTypeListener
is properly registered (and itself injected). The AdaptableTypeListener
will register a dedicated
com.google.inject.MembersInjector (AdapterInjector
) on all suitable
IAdaptable implementations it encounters.
Specifying the injection point (i.e. the <T> setAdapter(TypeToken<T>, T, String) method within a respective IAdaptable implementation is achieved by adding an @InjectAdapters annotation as follows:
public class MyAdaptable implements IAdaptable { @InjectAdapters public <T> void setAdapter(TypeToken<T> adapterType, T adapter, String role) { ... } }
Specifying the to be injected adapters is performed by means of map bindings in the com.google.inject.Module, which are qualified with an @AdapterMap annotation. In case the actual type of the to be registered adapter cannot be inferred from the adapter instance itself, or from the respective binding, information about the actual adapter type has to be provided via the AdapterKey used in all bindings. Where the type of an adapter can be inferred from the instance or the binding itself, it may be omitted.
public class MyModule extends AbstractModule { @Override protected void configure() { ... // obtain a map binder to bind adapters for the respective IAdaptable type. MapBinder<AdapterKey<?>, Object> adapterMapBinder = AdapterMaps.getAdapterMapBinder(binder(), MyAdaptable.class); // add adapter (map) binding for binding adapter 'a' of raw type 'A' with 'default' role to each MyAdaptable instance; // type information can be omitted, as it can be inferred from the adapter instance adapterMapBinder.addBinding(AdapterKey.defaultRole()).toInstance(a); // add adapter (map) binding for binding an instance of raw type 'A' with role 'r' to each MyAdaptable instance; // type information can be omitted, as it can be inferred from the binding adapterMapBinder.addBinding(AdapterKey.role("r").to(A.class); // add adapter (map) binding for binding adapter 'a' of parameterized type 'A<T>' with 'default' role to each MyAdaptable instance; // type information is required, as it cannot be inferred from the adapter instance, nor from the binding adapterMapBinder.addBinding(AdapterKey.get(new TypeToken<A<T>>(){})).toInstance(a); ... } }
When adapter map injection is properly enabled in the com.google.inject.Module, all suitable IAdaptable instances that are created through an com.google.inject.Injector, which is aware of the respective com.google.inject.Module, will be injected.
To this extend, the @AdapterMap
-bindings can be compared to the Guice
@Named-bindings, only that a
java.lang.Class instead of a
java.lang.String key is used. However, @AdapterMap
-bindings are more powerful, as they are evaluated polymorphically. That is, if a binding is specified for a specific
IAdaptable, let's say 'A', it will be evaluated for instances of all subtypes of 'A' as well, as long as they are suitable for injection (i.e. they directly or via inheritance provide a respective method eligible for adapter injection). This is a very powerful mechanism that is used intensively by the
GEF4 MVC component. It allows to register certain adapters already for some abstract base type, so that each concrete sub-type will be injected with a respective adapter instance.
An AdaptableScope
is a Guice
com.google.inject.Scope that is bound to an
IAdaptable instance. It can be used to scope the object instances (not limited to adapters) during injection. To enable this, bindings have to be 'scoped' and the scope has to be entered for the respective
IAdaptable instance before injection of adapters is triggered (which is supported best by using the AdaptableScopes
support class).
Scoping bindings can simply be performed in a Guice com.google.inject.Module as follows:
public class MyModule extends AbstractModule { @Override protected void configure() { ... // within the context of IAdaptable 'A', reuse a single instance of type 'B' binder().bind(B.class).in(AdaptableScopes.typed(A.class)); ... } }
In order for the scoping to work properly, the scope has to be bound to a certain adaptable before performing injection of objects:
// enter scope for IAdaptable 'a1' AdaptableScopes.enter(a1); // all injections are now performed in the context of 'a1' B b1 = injector.getInstance(B.class); // switch scope to IAdaptable 'a2' AdaptableScopes.enter(a2); // all injections are now performed in the context of 'a2' B b2 = injector.getInstance(B.class); // b2 != b1 // switch back context to 'a1' AdaptableScopes.switchTo(a1); B b3 = injector.getInstance(B.class); // b1 == b3
This mechanism is e.g. used by GEF4 MVC to scope the content models, which are adapters on a respective viewer. For instance, within the context of an IViewer, only one selection model instance should be used, no matter where it is injected; if an IBehavior e.g. uses members injection to obtain a reference to the selection model via a field, it should get the instance that is registered at its viewer.
The Notify package provides observable collections ( ObservableMap and ObservableList) and abstractions for respective observers ( IMapObserver and IListObserver).
An ObservableMap
is a specific Google Guava
com.google.common.collect.ForwardingMap, which adds support for observing changes via an IMapObserver
. It is e.g. used by
GEF4 Graph to make the attributes of Graph, Node, and Edge observable.
An ObservableList
is a specific Google Guava
com.google.common.collect.ForwardingList, which adds support for observing changes via an IListObserver
. It is e.g. used by
GEF4 Graph to make the edges and nodes of a Graph observable.
The Properties package provides abstractions and supporting classes to store and retrieve properties, as well as to notify about property changes.
An IPropertyChangeNotifier
provides facilities to register and unregister
PropertyChangeListeners. It may easily be implemented by using a
java.beans.PropertyChangeSupport as follows:
public class MyPropertyChangeNotifier implements IPropertyChangeNotifier { // create delegate private PropertyChangeSupport pcs = new PropertyChangeSupport(this); @Override public void addPropertyChangeListener(PropertyChangeListener listener) { pcs.addPropertyChangeListener(listener); } @Override public void removePropertyChangeListener(PropertyChangeListener listener) { pcs.removePropertyChangeListener(listener); } ... }
An IPropertyStore
provides facilities to store and retrieve arbitrary valued properties via
java.lang.String keys. Being an
IPropertyChangeNotifier, it is responsible of notifying any registered listeners about property value changes.
To enforce that implementers of
IPropertyStore properly follow the contract, PropertyStoreSupport
may be used. It does not formally implement the
IPropertyStore interface but provides implementations for all its methods and can thus be simply used as a delegate, as follows:
public class MyPropertyStore implements IPropertyStore { // create delegates private PropertyChangeSupport pcs = new PropertyChangeSupport(this); private PropertyStoreSupport pss = new PropertyStoreSupport(this, pcs); public void setProperty(String name, Object value) { pss.setProperty(name, value); } ... }
The Reflect package provides a utility class ( ReflectionUtils) that offers convenience operations in the context of Java reflection.
The ReflectionUtils
utilities provide support for getting and setting values of private fields by means of Java reflection.