org.springframework.core.ParameterizedTypeReference Maven / Gradle / Ivy
/*
* Copyright 2002-2018 the original author or authors.
*
* Licensed 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
*
* https://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 org.springframework.core;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import org.springframework.util.Assert;
/**
* The purpose of this class is to enable capturing and passing a generic
* {@link Type}. In order to capture the generic type and retain it at runtime,
* you need to create a subclass (ideally as anonymous inline class) as follows:
*
*
* ParameterizedTypeReference<List<String>> typeRef = new ParameterizedTypeReference<List<String>>() {};
*
*
* The resulting {@code typeRef} instance can then be used to obtain a {@link Type}
* instance that carries the captured parameterized type information at runtime.
* For more information on "super type tokens" see the link to Neal Gafter's blog post.
*
* @author Arjen Poutsma
* @author Rossen Stoyanchev
* @since 3.2
* @param the referenced type
* @see Neal Gafter on Super Type Tokens
*/
public abstract class ParameterizedTypeReference {
private final Type type;
protected ParameterizedTypeReference() {
Class parameterizedTypeReferenceSubclass = findParameterizedTypeReferenceSubclass(getClass());
Type type = parameterizedTypeReferenceSubclass.getGenericSuperclass();
Assert.isInstanceOf(ParameterizedType.class, type, "Type must be a parameterized type");
ParameterizedType parameterizedType = (ParameterizedType) type;
Type[] actualTypeArguments = parameterizedType.getActualTypeArguments();
Assert.isTrue(actualTypeArguments.length == 1, "Number of type arguments must be 1");
this.type = actualTypeArguments[0];
}
private ParameterizedTypeReference(Type type) {
this.type = type;
}
public Type getType() {
return this.type;
}
@Override
public boolean equals(Object other) {
return (this == other || (other instanceof ParameterizedTypeReference &&
this.type.equals(((ParameterizedTypeReference) other).type)));
}
@Override
public int hashCode() {
return this.type.hashCode();
}
@Override
public String toString() {
return "ParameterizedTypeReference<" + this.type + ">";
}
/**
* Build a {@code ParameterizedTypeReference} wrapping the given type.
* @param type a generic type (possibly obtained via reflection,
* e.g. from {@link java.lang.reflect.Method#getGenericReturnType()})
* @return a corresponding reference which may be passed into
* {@code ParameterizedTypeReference}-accepting methods
* @since 4.3.12
*/
public static ParameterizedTypeReference forType(Type type) {
return new ParameterizedTypeReference(type) {
};
}
private static Class findParameterizedTypeReferenceSubclass(Class child) {
Class parent = child.getSuperclass();
if (Object.class == parent) {
throw new IllegalStateException("Expected ParameterizedTypeReference superclass");
}
else if (ParameterizedTypeReference.class == parent) {
return child;
}
else {
return findParameterizedTypeReferenceSubclass(parent);
}
}
}