public abstract class OptionalBinder<T> extends Object
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, the optionals will be absent. Otherwise, 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.
public class FrameworkModule extends AbstractModule {
protected void configure() {
OptionalBinder.newOptionalBinder(binder(), Renamer.class);
}
}
With this module, an Optional
<Renamer>
can now be
injected. With no other bindings, the optional will be absent. However,
once a user adds a binding:
public class UserRenamerModule extends AbstractModule {
protected void configure() {
OptionalBinder.newOptionalBinder(binder(), Renamer.class)
.setBinding().to(ReplacingRenamer.class);
}
}
.. then the Optional<Renamer>
will be present and supply the
ReplacingRenamer.
Default values can be supplied using:
public class FrameworkModule extends AbstractModule {
protected void configure() {
OptionalBinder.newOptionalBinder(binder(), Key.get(String.class, LookupUrl.class))
.setDefault().to(DEFAULT_LOOKUP_URL);
}
}
With the above module, code can inject an @LookupUrl String
and it
will supply the DEFAULT_LOOKUP_URL. A user can change this value by binding
public class UserLookupModule extends AbstractModule {
protected void configure() {
OptionalBinder.newOptionalBinder(binder(), Key.get(String.class, LookupUrl.class))
.setBinding().to(CUSTOM_LOOKUP_URL);
}
}
... which will override the default value.Modifier and Type | Method and Description |
---|---|
static <T> OptionalBinder<T> |
newOptionalBinder(Binder binder,
Class<T> type) |
static <T> OptionalBinder<T> |
newOptionalBinder(Binder binder,
Key<T> type) |
static <T> OptionalBinder<T> |
newOptionalBinder(Binder binder,
TypeLiteral<T> type) |
abstract LinkedBindingBuilder<T> |
setBinding()
Returns a binding builder used to set the actual value that will be injected.
|
abstract LinkedBindingBuilder<T> |
setDefault()
Returns a binding builder used to set the default value that will be injected.
|
public static <T> OptionalBinder<T> newOptionalBinder(Binder binder, Class<T> type)
public static <T> OptionalBinder<T> newOptionalBinder(Binder binder, TypeLiteral<T> type)
public static <T> OptionalBinder<T> newOptionalBinder(Binder binder, Key<T> type)
public abstract LinkedBindingBuilder<T> setDefault()
setBinding()
is called.
It is an error to call this method without also calling one of the to
methods on the returned binding builder.
public abstract LinkedBindingBuilder<T> setBinding()
setDefault()
.
It is an error to call this method without also calling one of the to
methods on the returned binding builder.
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