Package javax.ws.rs.core

Class GenericEntity<T>

  • Type Parameters:
    T - response entity instance type
    public class GenericEntity<T>
extends Object
    Represents a message entity of a generic type T.

    Normally type erasure removes generic type information such that a Response instance that contains, e.g., an entity of type List<String> appears to contain a raw List<?> at runtime. When the generic type is required to select a suitable MessageBodyWriter, this class may be used to wrap the entity and capture its generic type.

    There are two ways to create an instance:

    1. Create a (typically anonymous) subclass of this class which enables retrieval of the type information at runtime despite type erasure. For example, the following code shows how to create a Response containing an entity of type List<String> whose generic type will be available at runtime for selection of a suitable MessageBodyWriter: 
      List<String> list = new ArrayList<String>();
 GenericEntity<List<String>> entity = new GenericEntity<List<String>>(list) {};
 Response response = Response.ok(entity).build();

      where list is the instance of List<String> that will form the response body and entity is an instance of an anonymous subclass of GenericEntity.

    2. Create an instance directly by supplying the generic type information with the entity. For example the following code shows how to create a response containing the result of a method invoked via reflection: 
      Method method = ...;
 GenericEntity<Object> entity = new GenericEntity<Object>(
    method.invoke(...), method.getGenericReturnType());
 Response response = Response.ok(entity).build();

      3. The above obtains the generic type from the return type of the method, the raw type is the class of entity.

    Since:
    1.0
    Author:
    Paul Sandoz, Marc Hadley
    See Also:
    GenericType

    • Constructor Detail

      • GenericEntity

        protected GenericEntity​(T entity)
        Constructs a new generic entity. Derives represented class from type parameter. Note that this constructor is protected, users should create a (usually anonymous) subclass as shown above.
        Parameters:
        entity - the entity instance, must not be null.
        Throws:
        IllegalArgumentException - if entity is null.

      • GenericEntity

        public GenericEntity​(T entity,
                     Type genericType)
        Create a new instance of GenericEntity, supplying the generic type information. The entity must be assignable to a variable of the supplied generic type, e.g. if entity is an instance of ArrayList<String> then genericType could be the same or a superclass of ArrayList with the same generic type like List<String>.
        Parameters:
        entity - the entity instance, must not be null.
        genericType - the generic type, must not be null.
        Throws:
        IllegalArgumentException - if the entity is not assignable to a variable of the supplied generic type or if entity or genericType is null.

    • Method Detail

      • getRawType

        public final Class<?> getRawType()
        Gets the raw type of the enclosed entity. Note that this is the raw type of the instance, not the raw type of the type parameter. I.e. in the example in the introduction, the raw type is ArrayList not List.
        Returns:
        the raw type.

      • getType

        public final Type getType()
        Gets underlying Type instance. Note that this is derived from the type parameter, not the enclosed instance. I.e. in the example in the introduction, the type is List<String> not ArrayList<String>.
        Returns:
        the type

      • getEntity

        public final T getEntity()
        Get the enclosed entity.
        Returns:
        the enclosed entity.

      • hashCode

        public int hashCode()
        Overrides:
        hashCode in class Object