OptionalBinder (Guice 4.1 API)
An API to bind optional values, optionally with a default value. OptionalBinder fulfills two roles:- It allows a framework to define an injection point that may or may not be bound by users.
- It allows a framework to supply a default value that can be changed by users.
When an OptionalBinder is added, it will always supply the bindings: Optional<T> and Optional<Provider<T>>. If setBinding() or setDefault() are called, it will also bind T.
setDefault is intended for use by frameworks that need a default value. User code can call setBinding to override the default. Warning: Even if setBinding is called, the default binding will still exist in the object graph. If it is a singleton, it will be instantiated in Stage.PRODUCTION.
If setDefault or setBinding are linked to Providers, the Provider may return null. If it does, the Optional bindings will be absent. Binding setBinding to a Provider that returns null will not cause OptionalBinder to fall back to the setDefault binding.
If neither setDefault nor setBinding are called, it will try to link to a user-supplied binding of the same type. If no binding exists, the optionals will be absent. Otherwise, if a user-supplied binding of that type exists, or if setBinding or setDefault are called, the optionals will return present if they are bound to a non-null value.
Values are resolved at injection time. If a value is bound to a provider, that provider's get method will be called each time the optional is injected (unless the binding is also scoped, or an optional of provider is injected).
Annotations are used to create different optionals of the same key/value type. Each distinct annotation gets its own independent binding.
Read full article from OptionalBinder (Guice 4.1 API)
No comments:
Post a Comment