/*
* Copyright 2002-2016 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
*
* 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 org.springframework.core.convert.support;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Member;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.Collections;
import java.util.Map;
import java.util.Set;
import org.springframework.core.convert.ConversionFailedException;
import org.springframework.core.convert.TypeDescriptor;
import org.springframework.core.convert.converter.ConditionalGenericConverter;
import org.springframework.util.ClassUtils;
import org.springframework.util.ConcurrentReferenceHashMap;
import org.springframework.util.ReflectionUtils;
/**
* Generic converter that uses conventions to convert a source object to a
* {@code targetType} by delegating to a method on the source object or to
* a static factory method or constructor on the {@code targetType}.
*
* <h3>Conversion Algorithm</h3>
* <ol>
* <li>Invoke a non-static {@code to[targetType.simpleName]()} method on the
* source object that has a return type equal to {@code targetType}, if such
* a method exists. For example, {@code org.example.Bar Foo#toBar()} is a
* method that follows this convention.
* <li>Otherwise invoke a <em>static</em> {@code valueOf(sourceType)} or Java
* 8 style <em>static</em> {@code of(sourceType)} or {@code from(sourceType)}
* method on the {@code targetType}, if such a method exists.
* <li>Otherwise invoke a constructor on the {@code targetType} that accepts
* a single {@code sourceType} argument, if such a constructor exists.
* <li>Otherwise throw a {@link ConversionFailedException}.
* </ol>
*
* <p><strong>Warning</strong>: this converter does <em>not</em> support the
* {@link Object#toString()} method for converting from a {@code sourceType}
* to {@code java.lang.String}. For {@code toString()} support, use
* {@link FallbackObjectToStringConverter} instead.
*
* @author Keith Donald
* @author Juergen Hoeller
* @author Sam Brannen
* @since 3.0
* @see FallbackObjectToStringConverter
*/
final class ObjectToObjectConverter implements ConditionalGenericConverter {
// Cache for the latest to-method resolved on a given Class
private static final Map<Class<?>, Member> conversionMemberCache =
new ConcurrentReferenceHashMap<>(32);
@Override
public Set<ConvertiblePair> getConvertibleTypes() {
return Collections.singleton(new ConvertiblePair(Object.class, Object.class));
}
@Override
public boolean matches(TypeDescriptor sourceType, TypeDescriptor targetType) {
return (sourceType.getType() != targetType.getType() &&
hasConversionMethodOrConstructor(targetType.getType(), sourceType.getType()));
}
@Override
public Object convert(Object source, TypeDescriptor sourceType, TypeDescriptor targetType) {
if (source == null) {
return null;
}
Class<?> sourceClass = sourceType.getType();
Class<?> targetClass = targetType.getType();
Member member = getValidatedMember(targetClass, sourceClass);
try {
if (member instanceof Method) {
Method method = (Method) member;
ReflectionUtils.makeAccessible(method);
if (!Modifier.isStatic(method.getModifiers())) {
return method.invoke(source);
}
else {
return method.invoke(null, source);
}
}
else if (member instanceof Constructor) {
Constructor<?> ctor = (Constructor<?>) member;
ReflectionUtils.makeAccessible(ctor);
return ctor.newInstance(source);
}
}
catch (InvocationTargetException ex) {
throw new ConversionFailedException(sourceType, targetType, source, ex.getTargetException());
}
catch (Throwable ex) {
throw new ConversionFailedException(sourceType, targetType, source, ex);
}
// If sourceClass is Number and targetClass is Integer, the following message should expand to:
// No toInteger() method exists on java.lang.Number, and no static valueOf/of/from(java.lang.Number)
// method or Integer(java.lang.Number) constructor exists on java.lang.Integer.
throw new IllegalStateException(String.format("No to%3$s() method exists on %1$s, " +
"and no static valueOf/of/from(%1$s) method or %3$s(%1$s) constructor exists on %2$s.",
sourceClass.getName(), targetClass.getName(), targetClass.getSimpleName()));
}
static boolean hasConversionMethodOrConstructor(Class<?> targetClass, Class<?> sourceClass) {
return (getValidatedMember(targetClass, sourceClass) != null);
}
private static Member getValidatedMember(Class<?> targetClass, Class<?> sourceClass) {
Member member = conversionMemberCache.get(targetClass);
if (isApplicable(member, sourceClass)) {
return member;
}
member = determineToMethod(targetClass, sourceClass);
if (member == null) {
member = determineFactoryMethod(targetClass, sourceClass);
if (member == null) {
member = determineFactoryConstructor(targetClass, sourceClass);
if (member == null) {
return null;
}
}
}
conversionMemberCache.put(targetClass, member);
return member;
}
private static boolean isApplicable(Member member, Class<?> sourceClass) {
if (member instanceof Method) {
Method method = (Method) member;
return (!Modifier.isStatic(method.getModifiers()) ?
ClassUtils.isAssignable(method.getDeclaringClass(), sourceClass) :
method.getParameterTypes()[0] == sourceClass);
}
else if (member instanceof Constructor) {
Constructor<?> ctor = (Constructor<?>) member;
return (ctor.getParameterTypes()[0] == sourceClass);
}
else {
return false;
}
}
private static Method determineToMethod(Class<?> targetClass, Class<?> sourceClass) {
if (String.class == targetClass || String.class == sourceClass) {
// Do not accept a toString() method or any to methods on String itself
return null;
}
Method method = ClassUtils.getMethodIfAvailable(sourceClass, "to" + targetClass.getSimpleName());
return (method != null && !Modifier.isStatic(method.getModifiers()) &&
ClassUtils.isAssignable(targetClass, method.getReturnType()) ? method : null);
}
private static Method determineFactoryMethod(Class<?> targetClass, Class<?> sourceClass) {
if (String.class == targetClass) {
// Do not accept the String.valueOf(Object) method
return null;
}
Method method = ClassUtils.getStaticMethod(targetClass, "valueOf", sourceClass);
if (method == null) {
method = ClassUtils.getStaticMethod(targetClass, "of", sourceClass);
if (method == null) {
method = ClassUtils.getStaticMethod(targetClass, "from", sourceClass);
}
}
return method;
}
private static Constructor<?> determineFactoryConstructor(Class<?> targetClass, Class<?> sourceClass) {
return ClassUtils.getConstructorIfAvailable(targetClass, sourceClass);
}
}