org.apache.tapestry5.ioc.services

## Interface MasterObjectProvider

- All Known Implementing Classes:
    MasterObjectProviderImpl

      @UsesOrderedConfiguration(value=ObjectProvider.class)
      public interface MasterObjectProvider

  A service that acts as a chain-of-command over a number of `ObjectProvider`, but allows for the case where no object may be provided. This service is itself a key part of Tapestry's general injection mechanism; it is used when instantiating a service implementation instance, invoking module methods (service builder, decorator, or contribution methods), when autobuilding objects of any type. As of Tapestry 5.3, the MasterObjectProvider allows injection of `OperationTracker` as a special case (not based on a contributed ObjectProvider).

- - ### Method Summary

    All Methods Instance Methods Abstract Methods
    Modifier and Type | Method and Description
    --- | ---
    `<T> T` | `provide(Class<T> objectType, AnnotationProvider annotationProvider, ObjectLocator locator, boolean required)` Provides an object based on an expression.

- - ### Method Detail

    - #### provide

          <T> T provide(Class<T> objectType,
                        AnnotationProvider annotationProvider,
                        ObjectLocator locator,
                        boolean required)

      Provides an object based on an expression. The process of providing objects occurs within a particular context, which will typically be a service builder method, service contributor method, or service decorator method. The locator parameter provides access to the services visible to that context. When the value is required and no `ObjectProvider` provided a non-null value, then `ObjectLocator.getService(Class, Class[])` is invoked (with no marker annotations), to provide a uniquely matching service, or throw a failure exception if no single service can be found.
      Type Parameters:
        `T` -
      Parameters:
        `objectType` - the expected object type
        `annotationProvider` - provides access to annotations (typically, the field or parameter to which an injection-related annotation is attached); annotations on the field or parameter may also be used when resolving the desired object
        `locator` - locator for the context in which the provider is being used
        `required` - if true (normal case) a value must be provided; if false then it is allowed for no ObjectProvider to provide a value, and this method may return null to indicate the failure
      Returns:
        the requested object, or null if this object provider can not supply an object
      Throws:
        `RuntimeException` - if the expression can not be evaluated, or the type of object identified is not assignable to the type specified by the objectType parameter

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