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179
...e-code-generation/src/main/java/pro/projo/internal/rcg/utilities/GenericTypeResolver.java
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| // // | ||
| // Copyright 2013 - 2024 Peter Walser, Mirko Raner // | ||
| // // | ||
| // 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 pro.projo.internal.rcg.utilities; | ||
|
|
||
| import java.lang.reflect.Method; | ||
| import java.lang.reflect.ParameterizedType; | ||
| import java.lang.reflect.Type; | ||
| import java.lang.reflect.TypeVariable; | ||
| import java.util.HashMap; | ||
| import java.util.LinkedList; | ||
| import java.util.List; | ||
| import java.util.Map; | ||
| import java.util.stream.Stream; | ||
| import static java.util.stream.Collectors.toList; | ||
|
|
||
| /** | ||
| * The {@link GenericTypeResolver} is a utility class whose main purpose is to encapsulate | ||
| * Peter Walser's generic type argument resolution code as found in | ||
| * <a href="https://stackoverflow.com/questions/17297308#answer-17301917">https://stackoverflow.com/questions/17297308#answer-17301917</a>. | ||
| * Per Stack Overflow's <a href="https://stackoverflow.com/legal/terms-of-service/public#licensing">licensing rules</a>, | ||
| * section 6, subsection "Subscriber Content", source code snippets posted on the site | ||
| * are licensed under <a href="https://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA 4.0</a> | ||
| * and are hereby further distributed under the Apache License, version 2.0, in a manner | ||
| * compatible with CC BY-SA 4.0, including full attribution of authorship. Author and | ||
| * copyright holder for the {@link #resolveActualTypeArgs(Class, Class, Type...)} | ||
| * method is <a href="https://stackoverflow.com/users/63293">Peter Walser</a>. | ||
| * | ||
| * @author Peter Walser | ||
| * @author Mirko Raner | ||
| **/ | ||
| public class GenericTypeResolver | ||
| { | ||
| /** | ||
| * Gets the actual return type of a method with respect to an actual type, including | ||
| * scenarios where the originally declared return type is a type variable. | ||
| * | ||
| * @param <T> the base type that contains the original method declaration | ||
| * @param originalMethodDeclaration the original {@link Method} declaration | ||
| * @param actualType the actual concrete type (must be a sub-type of {@code T}) | ||
| * @return the actual resolved return type (or the bounds type if there was no type variable binding) | ||
| **/ | ||
| public static <T> Type getReturnType(Method originalMethodDeclaration, Class<? extends T> actualType) | ||
| { | ||
| Type genericReturnType = originalMethodDeclaration.getGenericReturnType(); | ||
| if (genericReturnType instanceof TypeVariable) | ||
| { | ||
| String variableName = ((TypeVariable<?>)genericReturnType).getName(); | ||
| @SuppressWarnings("unchecked") | ||
| Class<T> baseClass = (Class<T>)originalMethodDeclaration.getDeclaringClass(); | ||
| TypeVariable<?>[] typeVariables = baseClass.getTypeParameters(); | ||
| List<String> variableNames = Stream.of(typeVariables).map(TypeVariable::getName).collect(toList()); | ||
| int variableIndex = variableNames.indexOf(variableName); | ||
| Class<? extends T> offspring = actualType; | ||
| Type[] resolvedTypeArguments = resolveActualTypeArgs(offspring, baseClass); | ||
| Type resolvedType = resolvedTypeArguments[variableIndex]; | ||
| if (resolvedType instanceof TypeVariable) | ||
| { | ||
| return originalMethodDeclaration.getReturnType(); | ||
| } | ||
| else | ||
| { | ||
| return resolvedType; | ||
| } | ||
| } | ||
| else | ||
| { | ||
| return genericReturnType; | ||
| } | ||
| } | ||
|
|
||
| /** | ||
| * Resolves the actual generic type arguments for a base class, as viewed from a subclass or implementation. | ||
| * | ||
| * @param <T> base type | ||
| * @param offspring class or interface subclassing or extending the base type | ||
| * @param base base class | ||
| * @param actualArgs the actual type arguments passed to the offspring class | ||
| * @return actual generic type arguments, must match the type parameters of the offspring class. If omitted, the | ||
| * type parameters will be used instead. | ||
| **/ | ||
| public static <T> Type[] resolveActualTypeArgs (Class<? extends T> offspring, Class<T> base, Type... actualArgs) | ||
| { | ||
| assert offspring != null; | ||
| assert base != null; | ||
| assert actualArgs.length == 0 || actualArgs.length == offspring.getTypeParameters().length; | ||
|
|
||
| // If actual types are omitted, the type parameters will be used instead. | ||
| if (actualArgs.length == 0) | ||
| { | ||
| actualArgs = offspring.getTypeParameters(); | ||
| } | ||
| // map type parameters into the actual types | ||
| Map<String, Type> typeVariables = new HashMap<String, Type>(); | ||
| for (int i = 0; i < actualArgs.length; i++) | ||
| { | ||
| TypeVariable<?> typeVariable = (TypeVariable<?>) offspring.getTypeParameters()[i]; | ||
| typeVariables.put(typeVariable.getName(), actualArgs[i]); | ||
| } | ||
|
|
||
| // Find direct ancestors (superclass, interfaces) | ||
| List<Type> ancestors = new LinkedList<Type>(); | ||
| if (offspring.getGenericSuperclass() != null) | ||
| { | ||
| ancestors.add(offspring.getGenericSuperclass()); | ||
| } | ||
| for (Type t: offspring.getGenericInterfaces()) | ||
| { | ||
| ancestors.add(t); | ||
| } | ||
|
|
||
| // Recurse into ancestors (superclass, interfaces) | ||
| for (Type type: ancestors) | ||
| { | ||
| if (type instanceof Class<?>) | ||
| { | ||
| // ancestor is non-parameterized. Recurse only if it matches the base class. | ||
| Class<?> ancestorClass = (Class<?>) type; | ||
| if (base.isAssignableFrom(ancestorClass)) | ||
| { | ||
| @SuppressWarnings("unchecked") | ||
| Type[] result = resolveActualTypeArgs((Class<? extends T>) ancestorClass, base); | ||
| if (result != null) | ||
| { | ||
| return result; | ||
| } | ||
| } | ||
| } | ||
| if (type instanceof ParameterizedType) | ||
| { | ||
| // ancestor is parameterized. Recurse only if the raw type matches the base class. | ||
| ParameterizedType parameterizedType = (ParameterizedType)type; | ||
| Type rawType = parameterizedType.getRawType(); | ||
| if (rawType instanceof Class<?>) | ||
| { | ||
| Class<?> rawTypeClass = (Class<?>) rawType; | ||
| if (base.isAssignableFrom(rawTypeClass)) | ||
| { | ||
| // loop through all type arguments and replace type variables with the actually known types | ||
| List<Type> resolvedTypes = new LinkedList<Type>(); | ||
| for (Type t: parameterizedType.getActualTypeArguments()) | ||
| { | ||
| if (t instanceof TypeVariable<?>) | ||
| { | ||
| Type resolvedType = typeVariables.get(((TypeVariable<?>)t).getName()); | ||
| resolvedTypes.add(resolvedType != null? resolvedType:t); | ||
| } else | ||
| { | ||
| resolvedTypes.add(t); | ||
| } | ||
| } | ||
|
|
||
| @SuppressWarnings("unchecked") | ||
| Type[] result = resolveActualTypeArgs((Class<? extends T>) rawTypeClass, base, resolvedTypes.toArray(new Type[] {})); | ||
| if (result != null) | ||
| { | ||
| return result; | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } | ||
|
|
||
| // we have a result if we reached the base class. | ||
| return offspring.equals(base) ? actualArgs : null; | ||
| } | ||
| } |
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