/*
* Copyright (c) 2011, 2017 Oracle and/or its affiliates. All rights reserved.
*
* Copyright (c) 2006 Google Inc.
*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
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 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:
- 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.
- 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.
Author: Paul Sandoz, Marc Hadley Type parameters: - <T> – response entity instance type
See Also: Since: 1.0
/**
* Represents a message entity of a generic type {@code T}.
* <p>
* Normally type erasure removes generic type information such that a
* {@link Response} instance that contains, e.g., an entity of type
* {@code List<String>} 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.
* </p>
* <p>
* There are two ways to create an instance:
* </p>
* <ol>
* <li>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<String>} whose
* generic type will be available at runtime for selection of a suitable
* {@link javax.ws.rs.ext.MessageBodyWriter}:
*
* <pre>List<String> list = new ArrayList<String>();
* GenericEntity<List<String>> entity = new GenericEntity<List<String>>(list) {};
* Response response = Response.ok(entity).build();</pre>
*
* <p>where {@code list} is the instance of {@code List<String>}
* that will form the response body and entity is an instance of an anonymous
* subclass of {@code GenericEntity}.</p></li>
* <li>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:
* <pre>Method method = ...;
* GenericEntity<Object> entity = new GenericEntity<Object>(
* method.invoke(...), method.getGenericReturnType());
* Response response = Response.ok(entity).build();</pre></li>
* <p>The above obtains the generic type from the return type of the method,
* the raw type is the class of entity.</p>
* </ol>
*
* @param <T> response entity instance type
* @author Paul Sandoz
* @author Marc Hadley
* @see GenericType
* @since 1.0
*/
public class GenericEntity<T> {
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.
Params: - entity – the entity instance, must not be
null.
Throws: - IllegalArgumentException – if entity is
null.
/**
* 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 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>. Params: - 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.
/**
* 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<String>} then {@code genericType} could
* be the same or a superclass of {@code ArrayList} with the same generic
* type like {@code List<String>}.
*
* @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 ArrayList not List. Returns: the raw type.
/**
* 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 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
/**
* 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<String>} not
* {@code ArrayList<String>}.
*
* @return the type
*/
public final Type getType() {
return type;
}
Get the enclosed entity.
Returns: the enclosed entity.
/**
* 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() + "}";
}
}