org.ldp4j.application.ext.Generics Maven / Gradle / Ivy
/**
* #-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=#
* This file is part of the LDP4j Project:
* http://www.ldp4j.org/
*
* Center for Open Middleware
* http://www.centeropenmiddleware.com/
* #-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=#
* Copyright (C) 2014-2016 Center for Open Middleware.
* #-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=#
* 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.
* #-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=#
* Artifact : org.ldp4j.framework:ldp4j-application-api:0.2.1
* Bundle : ldp4j-application-api-0.2.1.jar
* #-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=#
*/
package org.ldp4j.application.ext;
import static com.google.common.base.Preconditions.checkNotNull;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.lang.reflect.TypeVariable;
/**
* Helper methods for class type parameters.
*
* @see Super
* Type Tokens
*/
final class Generics {
private Generics() {
/* singleton */
}
/**
* Finds the type parameter for the given class.
*
* @param klass
* a parameterized class
* @return the class's type parameter
*/
static Class getTypeParameter(Class klass) {
return getTypeParameter(klass, Object.class);
}
/**
* Finds the type parameter for the given class which is assignable to the
* bound class.
*
* @param clazz
* a parameterized class
* @param bound
* the type bound
* @param
* the type bound
* @return the class's type parameter
*/
static Class getTypeParameter(Class clazz, Class bound) {
Type t = checkNotNull(clazz);
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) {
Class result=processParameterizedType(bound, (ParameterizedType) t);
if(result!=null) {
return result;
}
}
throw new IllegalStateException("Cannot figure out type parameterization for "+ clazz.getName());
}
protected static Class processParameterizedType(Class bound, ParameterizedType parameterizedType) {
// should typically have one of type parameter (first one) that matches:
for(Type param : parameterizedType.getActualTypeArguments()) {
Class cls = null;
if(param instanceof Class) {
cls=determineClass(bound, param);
} else if(param instanceof TypeVariable) {
cls=processTypeVariable(bound, (TypeVariable)param);
}
if(cls!=null) {
return cls;
}
}
return null;
}
protected static Class processTypeVariable(Class bound, TypeVariable typeVariable) {
for(Type paramBound:typeVariable.getBounds()) {
if(paramBound instanceof Class) {
Classcls=determineClass(bound,paramBound);
if(cls!=null) {
return cls;
}
}
}
return null;
}
@SuppressWarnings("unchecked")
private static Class determineClass(Class bound, Type candidate) {
if (candidate instanceof Class) {
final Class cls = (Class) candidate;
if (bound.isAssignableFrom(cls)) {
return (Class) cls;
}
}
return null;
}
}