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package javax.ws.rs.core;

import java.lang.reflect.GenericArrayType;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;

/**
 * Represents a message entity of a generic type {@code T}.
 * 

* Normally type erasure removes generic type information such that a * {@link Response} instance that contains, e.g., an entity of type * {@code List} appears to contain a raw {@code List} at runtime. * When the generic type is required to select a suitable * {@link javax.ws.rs.ext.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 * {@link Response} containing an entity of type {@code List} whose * generic type will be available at runtime for selection of a suitable * {@link javax.ws.rs.ext.MessageBodyWriter}: * *
    List<String> list = new ArrayList<String>();
     * GenericEntity<List<String>> entity = new GenericEntity<List<String>>(list) {};
     * Response response = Response.ok(entity).build();
    * *

    where {@code list} is the instance of {@code List} * that will form the response body and entity is an instance of an anonymous * subclass of {@code GenericEntity}.

  2. *
  3. 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();
  4. *

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

    *
* * @param response entity instance type * @author Paul Sandoz * @author Marc Hadley * @see GenericType * @since 1.0 */ public class GenericEntity { private final Class rawType; private final Type type; private final 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. * * @param entity the entity instance, must not be {@code null}. * @throws IllegalArgumentException if entity is {@code null}. */ protected GenericEntity(final T entity) { if (entity == null) { throw new IllegalArgumentException("The entity must not be null"); } this.entity = entity; this.type = GenericType.getTypeArgument(getClass(), GenericEntity.class); this.rawType = entity.getClass(); } /** * 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 {@code entity} is an instance of * {@code ArrayList} then {@code genericType} could * be the same or a superclass of {@code ArrayList} with the same generic * type like {@code List}. * * @param entity the entity instance, must not be {@code null}. * @param genericType the generic type, must not be {@code null}. * @throws IllegalArgumentException if the entity is not assignable to * a variable of the supplied generic type or if entity or genericType * is null. */ public GenericEntity(final T entity, final Type genericType) { if (entity == null || genericType == null) { throw new IllegalArgumentException("Arguments must not be null."); } this.entity = entity; this.rawType = entity.getClass(); checkTypeCompatibility(this.rawType, genericType); this.type = genericType; } private void checkTypeCompatibility(final Class c, final Type t) { if (t instanceof Class) { Class ct = (Class) t; if (ct.isAssignableFrom(c)) { return; } } else if (t instanceof ParameterizedType) { ParameterizedType pt = (ParameterizedType) t; Type rt = pt.getRawType(); checkTypeCompatibility(c, rt); return; } else if (c.isArray() && (t instanceof GenericArrayType)) { GenericArrayType at = (GenericArrayType) t; Type rt = at.getGenericComponentType(); checkTypeCompatibility(c.getComponentType(), rt); return; } throw new IllegalArgumentException("The type is incompatible with the class of the entity."); } /** * 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 {@code ArrayList} not {@code List}. * * @return the raw type. */ public final Class getRawType() { return rawType; } /** * Gets underlying {@code 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 {@code List} not * {@code ArrayList}. * * @return the type */ public final Type getType() { return type; } /** * Get the enclosed entity. * * @return the enclosed entity. */ public final T getEntity() { return entity; } @Override public boolean equals(Object obj) { boolean result = this == obj; if (!result && obj instanceof GenericEntity) { // Compare inner type for equality GenericEntity that = (GenericEntity) obj; return this.type.equals(that.type) && this.entity.equals(that.entity); } return result; } @Override public int hashCode() { return entity.hashCode() + type.hashCode() * 37 + 5; } @Override public String toString() { return "GenericEntity{" + entity.toString() + ", " + type.toString() + "}"; } }




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