org.springframework.core.convert.support.ObjectToObjectConverter Maven / Gradle / Ivy
/*
* Copyright 2002-2015 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.Method;
import java.util.Collections;
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.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}.
*
* Conversion Algorithm
*
* - Invoke a {@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.
*
- Otherwise invoke a static {@code valueOf(sourceType)} or Java
* 8 style static {@code of(sourceType)} or {@code from(sourceType)}
* method on the {@code targetType}, if such a method exists.
*
- Otherwise invoke a constructor on the {@code targetType} that accepts
* a single {@code sourceType} argument, if such a constructor exists.
*
- Otherwise throw a {@link ConversionFailedException}.
*
*
* Warning: this converter does not 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 {
@Override
public Set getConvertibleTypes() {
return Collections.singleton(new ConvertiblePair(Object.class, Object.class));
}
@Override
public boolean matches(TypeDescriptor sourceType, TypeDescriptor targetType) {
if (sourceType.getType().equals(targetType.getType())) {
// no conversion required
return false;
}
return (String.class == targetType.getType() ?
hasFactoryConstructor(String.class, sourceType.getType()) :
hasToMethodOrFactoryMethodOrConstructor(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();
try {
// Do not invoke a toString() method
if (String.class != targetClass) {
Method method = getToMethod(targetClass, sourceClass);
if (method != null) {
ReflectionUtils.makeAccessible(method);
return method.invoke(source);
}
}
Method method = getFactoryMethod(targetClass, sourceClass);
if (method != null) {
ReflectionUtils.makeAccessible(method);
return method.invoke(null, source);
}
Constructor constructor = getFactoryConstructor(targetClass, sourceClass);
if (constructor != null) {
return constructor.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, then the following message
// format 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.
String message = 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());
throw new IllegalStateException(message);
}
private static Method getToMethod(Class targetClass, Class sourceClass) {
Method method = ClassUtils.getMethodIfAvailable(sourceClass, "to" + targetClass.getSimpleName());
return (method != null && targetClass.equals(method.getReturnType()) ? method : null);
}
private static Method getFactoryMethod(Class targetClass, Class sourceClass) {
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 getFactoryConstructor(Class targetClass, Class sourceClass) {
return ClassUtils.getConstructorIfAvailable(targetClass, sourceClass);
}
private static boolean hasToMethodOrFactoryMethodOrConstructor(Class targetClass,
Class sourceClass) {
return (hasToMethod(targetClass, sourceClass) ||
hasFactoryMethod(targetClass, sourceClass) ||
hasFactoryConstructor(targetClass, sourceClass));
}
static boolean hasToMethod(Class targetClass, Class sourceClass) {
return getToMethod(targetClass, sourceClass) != null;
}
static boolean hasFactoryMethod(Class targetClass, Class sourceClass) {
return getFactoryMethod(targetClass, sourceClass) != null;
}
static boolean hasFactoryConstructor(Class targetClass, Class sourceClass) {
return getFactoryConstructor(targetClass, sourceClass) != null;
}
}