com.google.inject.multibindings

Class MapBinder<K,V>


  • public class MapBinder<K,V>
extends Object
    An API to bind multiple map entries separately, only to later inject them as a complete map. MapBinder is intended for use in your application's module: 
    
 public class SnacksModule extends AbstractModule {
   protected void configure() {
     MapBinder<String, Snack> mapbinder
         = MapBinder.newMapBinder(binder(), String.class, Snack.class);
     mapbinder.addBinding("twix").toInstance(new Twix());
     mapbinder.addBinding("snickers").toProvider(SnickersProvider.class);
     mapbinder.addBinding("skittles").to(Skittles.class);
   }
 }

    With this binding, a Map<String, Snack> can now be injected: 

    
 class SnackMachine {
   @Inject
   public SnackMachine(Map<String, Snack> snacks) { ... }
 }

    In addition to binding Map<K, V>, a mapbinder will also bind Map<K, Provider<V>> for lazy value provision: 

    
 class SnackMachine {
   @Inject
   public SnackMachine(Map<String, Provider<Snack>> snackProviders) { ... }
 }

    Contributing mapbindings from different modules is supported. For example, it is okay to have both CandyModule and ChipsModule both create their own MapBinder<String, Snack>, and to each contribute bindings to the snacks map. When that map is injected, it will contain entries from both modules.

    The map's iteration order is consistent with the binding order. This is convenient when multiple elements are contributed by the same module because that module can order its bindings appropriately. Avoid relying on the iteration order of elements contributed by different modules, since there is no equivalent mechanism to order modules.

    The map is unmodifiable. Elements can only be added to the map by configuring the MapBinder. Elements can never be removed from the map.

    Values are resolved at map injection time. If a value is bound to a provider, that provider's get method will be called each time the map is injected (unless the binding is also scoped, or a map of providers is injected).

    Annotations are used to create different maps of the same key/value type. Each distinct annotation gets its own independent map.

    Keys must be distinct. If the same key is bound more than once, map injection will fail. However, use permitDuplicates() in order to allow duplicate keys; extra bindings to Map<K, Set<V>> and Map<K, Set<Provider<V>> will be added.

    Keys must be non-null. addBinding(null) will throw an unchecked exception.

    Values must be non-null to use map injection. If any value is null, map injection will fail (although injecting a map of providers will not).

    Author:
    dpb@google.com (David P. Baker)

    • Method Detail

      • newMapBinder

        public static <K,V> MapBinder<K,V> newMapBinder(Binder binder,
                                TypeLiteral<K> keyType,
                                TypeLiteral<V> valueType)
        Returns a new mapbinder that collects entries of keyType/valueType in a Map that is itself bound with no binding annotation.

      • newMapBinder

        public static <K,V> MapBinder<K,V> newMapBinder(Binder binder,
                                Class<K> keyType,
                                Class<V> valueType)
        Returns a new mapbinder that collects entries of keyType/valueType in a Map that is itself bound with no binding annotation.

      • newMapBinder

        public static <K,V> MapBinder<K,V> newMapBinder(Binder binder,
                                TypeLiteral<K> keyType,
                                TypeLiteral<V> valueType,
                                Annotation annotation)
        Returns a new mapbinder that collects entries of keyType/valueType in a Map that is itself bound with annotation.

      • newMapBinder

        public static <K,V> MapBinder<K,V> newMapBinder(Binder binder,
                                Class<K> keyType,
                                Class<V> valueType,
                                Annotation annotation)
        Returns a new mapbinder that collects entries of keyType/valueType in a Map that is itself bound with annotation.

      • newMapBinder

        public static <K,V> MapBinder<K,V> newMapBinder(Binder binder,
                                TypeLiteral<K> keyType,
                                TypeLiteral<V> valueType,
                                Class<? extends Annotation> annotationType)
        Returns a new mapbinder that collects entries of keyType/valueType in a Map that is itself bound with annotationType.

      • newMapBinder

        public static <K,V> MapBinder<K,V> newMapBinder(Binder binder,
                                Class<K> keyType,
                                Class<V> valueType,
                                Class<? extends Annotation> annotationType)
        Returns a new mapbinder that collects entries of keyType/valueType in a Map that is itself bound with annotationType.

      • permitDuplicates

        public MapBinder<K,V> permitDuplicates()
        Configures the MapBinder to handle duplicate entries.

        When multiple equal keys are bound, the value that gets included in the map is arbitrary.

        In addition to the Map<K, V> and Map<K, Provider<V>> maps that are normally bound, a Map<K, Set<V>> and Map<K, Set<Provider<V>>> are also bound, which contain all values bound to each key.

        When multiple modules contribute elements to the map, this configuration option impacts all of them.

        Returns:
        this map binder
        Since:
        3.0

      • addBinding

        public LinkedBindingBuilder<V> addBinding(K key)
        Returns a binding builder used to add a new entry in the map. Each key must be distinct (and non-null). Bound providers will be evaluated each time the map is injected.

        It is an error to call this method without also calling one of the to methods on the returned binding builder.

        Scoping elements independently is supported. Use the in method to specify a binding scope.

      • hashCode

        public int hashCode()
        Overrides:
        hashCode in class Object

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