/*
* Copyright (c) 2012 S.C. Axemblr Software Solutions S.R.L
*
* 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
*
* 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 com.axemblr.provisionr.test;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import static com.google.common.base.Preconditions.checkNotNull;
/**
* Helper methods for class type parameters.
*
* @see <a href="https://github.com/codahale/dropwizard/blob/master/dropwizard-core/src/main/java/com/yammer/dropwizard/util/Generics.java">Generics in Codahale Dropwizard</a>
* @see <a href="http://gafter.blogspot.com/2006/12/super-type-tokens.html">Super Type Tokens</a>
*/
public class Generics {
private Generics() { /* singleton */ }
/**
* Finds the type parameter for the given class which is assignable to the bound class.
*
* @param klass a parameterized class
* @param bound the type bound
* @param <T> the type bound
* @return the class's type parameter
*/
@SuppressWarnings("unchecked")
public static <T> Class<T> getTypeParameter(Class<?> klass, Class<? super T> bound) {
Type t = checkNotNull(klass);
while (t instanceof Class<?>) {
t = ((Class<?>) t).getGenericSuperclass();
}
/* This is not guaranteed to work for all cases with convoluted piping
* of type parameters: but it can at least resolve straight-forward
* extension with single type parameter (as per [Issue-89]).
* And when it fails to do that, will indicate with specific exception.
*/
if (t instanceof ParameterizedType) {
// should typically have one of type parameters (first one) that matches:
for (Type param : ((ParameterizedType) t).getActualTypeArguments()) {
if (param instanceof Class<?>) {
final Class<?> cls = (Class<?>) param;
if (bound.isAssignableFrom(cls)) {
return (Class<T>) cls;
}
}
}
}
throw new IllegalStateException("Cannot figure out type parameterization for " + klass.getName());
}
/**
* Finds the type parameter for the given class.
*
* @param klass a parameterized class
* @return the class's type parameter
*/
public static Class<?> getTypeParameter(Class<?> klass) {
return getTypeParameter(klass, Object.class);
}
}