ReflectionUtils.java
/*
* *************************************************************************************************************************************************************
*
* TheseFoolishThings: Miscellaneous utilities
* http://tidalwave.it/projects/thesefoolishthings
*
* Copyright (C) 2009 - 2025 by Tidalwave s.a.s. (http://tidalwave.it)
*
* *************************************************************************************************************************************************************
*
* 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.
*
* *************************************************************************************************************************************************************
*
* git clone https://bitbucket.org/tidalwave/thesefoolishthings-src
* git clone https://github.com/tidalwave-it/thesefoolishthings-src
*
* *************************************************************************************************************************************************************
*/
package it.tidalwave.util;
import java.lang.annotation.Annotation;
import java.lang.reflect.Array;
import java.lang.reflect.Field;
import java.lang.reflect.GenericArrayType;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.lang.reflect.TypeVariable;
import jakarta.annotation.Nonnull;
import jakarta.annotation.Nullable;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import lombok.extern.slf4j.Slf4j;
import static java.util.Objects.requireNonNull;
import static java.util.stream.Collectors.*;
import static it.tidalwave.util.ShortNames.*;
/***************************************************************************************************************************************************************
*
* Adapted from <a href="http://www.artima.com/weblogs/viewpost.jsp?thread=208860">this article</a>
*
* @author Ian Robertson
* @author Fabrizio Giudici
*
**************************************************************************************************************************************************************/
@Slf4j
public class ReflectionUtils
{
private static final List<String> INJECT_CLASS_NAMES = List.of("javax.inject.Inject", "jakarta.inject.Inject");
/***********************************************************************************************************************************************************
* Get the actual type arguments a subclass has used to extend a generic base class. Note: if the base class is an interface, this method will work only
* if it is the first inherited interface in childClass.
*
* @param <T> the static type of the base class
* @param baseClass the base class
* @param childClass the subclass
* @return a list of the raw classes for the actual type arguments.
**********************************************************************************************************************************************************/
@Nonnull
public static <T> List<Class<?>> getTypeArguments (@Nonnull final Class<T> baseClass,
@Nonnull final Class<? extends T> childClass)
{
final Map<Type, Type> resolvedTypes = new HashMap<>();
Type type = childClass;
// start walking up the inheritance hierarchy until we hit baseClass
while (!baseClass.equals(getClass(type)))
{
if (type instanceof Class<?>)
{
if (baseClass.isInterface())
{
type = ((Class<?>)type).getGenericInterfaces()[0]; // FIXME: works only for one interface in hierarchy
}
else
{
type = ((Class<?>)type).getGenericSuperclass();
}
// there is no useful information for us in raw types, so just keep going.
}
else
{
final var parameterizedType = (ParameterizedType) type;
final var rawType = (Class<?>) parameterizedType.getRawType();
final var actualTypeArguments = parameterizedType.getActualTypeArguments();
final TypeVariable<?>[] typeParameters = rawType.getTypeParameters();
for (var i = 0; i < actualTypeArguments.length; i++)
{
resolvedTypes.put(typeParameters[i], actualTypeArguments[i]);
}
if (!rawType.equals(baseClass))
{
type = rawType.getGenericSuperclass();
}
}
}
// finally, for each actual type argument provided to baseClass, determine (if possible)
// the raw class for that type argument.
final Type[] actualTypeArguments;
if (type instanceof Class)
{
actualTypeArguments = ((Class<?>)type).getTypeParameters();
}
else
{
actualTypeArguments = ((ParameterizedType)type).getActualTypeArguments();
}
final var typeArgumentsAsClasses = new ArrayList<Class<?>>();
// resolve types by chasing down type variables.
for (var baseType : actualTypeArguments)
{
while (resolvedTypes.containsKey(baseType))
{
baseType = resolvedTypes.get(baseType);
}
typeArgumentsAsClasses.add(getClass(baseType));
}
return typeArgumentsAsClasses;
}
/***********************************************************************************************************************************************************
* Instantiates an object of the given class performing dependency injections through the constructor.
*
* @param <T> the generic type of the object to instantiate
* @param type the dynamic type of the object to instantiate; it is expected to have a single constructor
* @param beans the bag of objects to instantiate
* @return the new instance
* @throws RuntimeException if something fails
* @since 3.2-ALPHA-17
**********************************************************************************************************************************************************/
public static <T> T instantiateWithDependencies (@Nonnull final Class<? extends T> type,
@Nonnull final Map<Class<?>, Object> beans)
{
try
{
log.debug("instantiateWithDependencies({}, {})", shortName(type), shortIds(beans.values()));
final var constructors = type.getConstructors();
if (constructors.length > 1)
{
throw new RuntimeException("Multiple constructors in " + type);
}
final var parameters = Arrays.stream(constructors[0].getParameterTypes()).map(beans::get).collect(toList());
log.trace(">>>> ctor arguments: {}", shortIds(parameters));
return type.cast(constructors[0].newInstance(parameters.toArray()));
}
catch (InstantiationException | IllegalAccessException | InvocationTargetException e)
{
throw new RuntimeException(e);
}
}
/***********************************************************************************************************************************************************
* Performs dependency injection to an object by means of field introspection.
*
* @param object the object
* @param beans the bag of objects to instantiate
* @since 3.2-ALPHA-17
**********************************************************************************************************************************************************/
public static void injectDependencies (@Nonnull final Object object, @Nonnull final Map<Class<?>, Object> beans)
{
for (final var field : object.getClass().getDeclaredFields())
{
if (hasInjectAnnotation(field))
{
field.setAccessible(true);
final var type = field.getType();
final var dependency = beans.get(type);
if (dependency == null)
{
throw new RuntimeException("Can't inject " + object + "." + field.getName());
}
try
{
field.set(object, dependency);
}
catch (IllegalArgumentException | IllegalAccessException e)
{
throw new RuntimeException(e);
}
}
}
}
/***********************************************************************************************************************************************************
* Returns the class literal associated to the given type.
*
* @param type the type to inspect
* @return the class literal; it might be {@code null} if fails
**********************************************************************************************************************************************************/
@Nullable
public static Class<?> getClass (@Nonnull final Type type)
{
requireNonNull(type, "type");
if (type instanceof Class<?>)
{
return (Class<?>)type;
}
else if (type instanceof ParameterizedType)
{
return getClass(((ParameterizedType)type).getRawType());
}
else if (type instanceof GenericArrayType)
{
final var componentType = ((GenericArrayType)type).getGenericComponentType();
final var componentClass = getClass(componentType);
if (componentClass == null)
{
return null;
}
return Array.newInstance(componentClass, 0).getClass();
}
else
{
// throw new IllegalArgumentException(type.toString());
return null;
}
}
/***********************************************************************************************************************************************************
*
**********************************************************************************************************************************************************/
private static boolean hasInjectAnnotation (@Nonnull final Field field)
{
final var classLoader = Thread.currentThread().getContextClassLoader();
for (final var className : INJECT_CLASS_NAMES)
{
try
{
@SuppressWarnings("unchecked")
final var clazz = (Class<? extends Annotation>)classLoader.loadClass(className);
if (field.getAnnotation(clazz) != null)
{
return true;
}
}
catch (ClassNotFoundException ignored)
{
// try next
}
}
return false;
}
}