javax.ws.rs.core

Class GenericEntity<T>

java.lang.Object

javax.ws.rs.core.GenericEntity<T>

public class GenericEntity<T>
extends java.lang.Object

Represents a response 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();

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

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	GenericEntity(T entity) Constructs a new generic entity.
	GenericEntity(T entity, java.lang.reflect.Type genericType) Create a new instance of GenericEntity, supplying the generic type information.

Method Summary

Methods

Modifier and Type	Method and Description
T	getEntity() Get the enclosed entity
java.lang.Class<?>	getRawType() Gets the raw type of the enclosed entity.
java.lang.reflect.Type	getType() Gets underlying Type instance.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

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:

java.lang.IllegalArgumentException - if entity is null

GenericEntity

public GenericEntity(T entity,
             java.lang.reflect.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:

java.lang.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 java.lang.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 java.lang.reflect.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