Package hu.ibello.inject

This package contains API elements for the Ibello dependency injection system.

See: Description

Interface Summary

Interface	Description
Initializable	This interface marks an initializable object.

Enum Summary

Enum	Description
Scope	This enum specifies the scope of a dependency injection.

Annotation Types Summary

Annotation Type	Description
Inject	Main annotation of the dependency injection system.
Injectable	Marks an injectable class and specifies the scope of the injection.

Package hu.ibello.inject Description

This package contains API elements for the Ibello dependency injection system.

Ibello Dependency Injection System

In ibello, all dependency injections are performed by the injector. The injector discovers the injectable fields and handles their values. Sometimes a new instance will be created, and sometimes a previously created instance will be used again.

The dependency injection is based on annotations.

• The Inject annotation marks injectable fields in classes.

• The Injectable annotation marks classes suitable for injection. The value of the annotation is the scope of the injection. It's one of the constants from Scope type. During the injection, the injector tries to use a previously created instance from the same scope. Eg. if the injected class is test-scoped, then only instance created during the same test method execution is valid for injection. If there is no valid instance, then the injector creates a new one.

  If the injected class does not have a scope annotation, then the injector tries to determine the scope from it's superclasses. The scope will be inherited from the nearest superclass which has a scope annotation. If none of the superclasses has scope annotation, then the class will be considered as session-scoped.

The test execution consists of different stages. These are:

• Session: each thread defines it's own session. The session lasts until the thread is running.
• Specification: contains all test runs in the same test class. The specification lasts while it's test methods are not finished.
• Test: valid only for the execution of a single test method.

Instances of session-scoped classes are valid only for a session. In a new session, whole new instances will be created. Similarly, instances of specification-scoped classes are valid for a specification execution, and instances of test-scoped classes are valid for a single test run. Singleton instances do not lose they validity, so a singleton class has only one instance for the entire program run.

Not all injections can be performed successfully. If the scope of the parent class is bigger that the scope of the injected field, the the injection is forbidden and will result a runtime exception. So you can't inject specification-scoped instances into a session-scoped class.

The injected class should have a default constructor. The injector calls this constructor if a new instance is needed for this class.

If the injected class implements the Initializable interface, and the injector creates a new instance, then the Initializable#initialize() method will be called automatically on that instance.

During the injection these steps will be performed in the given order:

1. The injector determines if the field needs a new instance, or an existing instance should be used.
2. If an existing instance should be used, then the injector assings that instance to the field, and the injection process ends.
3. If a new instance should be created, then the injector creates that instance with the default constructor of the injected class.
4. The injector performs a full injection process on the new instance, discovers it's injectable fields and assigns values to them.
5. If the injected class implements the Initializable interface, then the Initializable#initialize() method will be called.
6. The injection process for that field ends.

Author:

Kornél Simon