org.springframework.core.ReflectiveVisitorHelper Maven / Gradle / Ivy
/*
* Copyright 2002-2005 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;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.LinkedList;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.util.Assert;
import org.springframework.util.CachingMapDecorator;
import org.springframework.util.ReflectionUtils;
/**
* Helper implementation for a reflective visitor.
* Mainly for internal use within the framework.
*
* To use, call invokeVisit, passing a Visitor object
* and the data argument to accept (double-dispatch). For example:
*
*
* public String styleValue(Object value) {
* reflectiveVistorSupport.invokeVisit(this, value)
* }
*
* // visit call back will be invoked via reflection
* String visit(<valueType> arg) {
* // process argument of type <valueType>
* }
*
*
* See the DefaultValueStyler class for a concrete usage.
*
* @author Keith Donald
* @since 1.2.2
* @see org.springframework.core.style.DefaultValueStyler
*/
public final class ReflectiveVisitorHelper {
private static final String VISIT_METHOD = "visit";
private static final String VISIT_NULL = "visitNull";
private static final Log logger = LogFactory.getLog(ReflectiveVisitorHelper.class);
private CachingMapDecorator visitorClassVisitMethods = new CachingMapDecorator() {
public Object create(Object key) {
return new ClassVisitMethods((Class) key);
}
};
/**
* Use reflection to call the appropriate visit method
* on the provided visitor, passing in the specified argument.
* @param visitor the visitor encapsulating the logic to process the argument
* @param argument the argument to dispatch
* @throws IllegalArgumentException if the visitor parameter is null
*/
public Object invokeVisit(Object visitor, Object argument) {
Assert.notNull(visitor, "The visitor to visit is required");
// Perform call back on the visitor through reflection.
Method method = getMethod(visitor.getClass(), argument);
if (method == null) {
if (logger.isWarnEnabled()) {
logger.warn("No method found by reflection for visitor class [" + visitor.getClass().getName()
+ "] and argument of type [" + (argument != null ? argument.getClass().getName() : "") + "]");
}
return null;
}
try {
Object[] args = null;
if (argument != null) {
args = new Object[] { argument };
}
if (!Modifier.isPublic(method.getModifiers()) && !method.isAccessible()) {
method.setAccessible(true);
}
return method.invoke(visitor, args);
}
catch (Exception ex) {
ReflectionUtils.handleReflectionException(ex);
throw new IllegalStateException("Should never get here");
}
}
/**
* Determines the most appropriate visit method for the
* given visitor class and argument.
*/
private Method getMethod(Class visitorClass, Object argument) {
ClassVisitMethods visitMethods = (ClassVisitMethods) this.visitorClassVisitMethods.get(visitorClass);
return visitMethods.getVisitMethod(argument != null ? argument.getClass() : null);
}
/**
* Internal class caching visitor methods by argument class.
*/
private static class ClassVisitMethods {
private final Class visitorClass;
private CachingMapDecorator visitMethodCache = new CachingMapDecorator() {
public Object create(Object argumentClazz) {
if (argumentClazz == null) {
return findNullVisitorMethod();
}
Method method = findVisitMethod((Class)argumentClazz);
if (method == null) {
method = findDefaultVisitMethod();
}
return method;
}
};
private ClassVisitMethods(Class visitorClass) {
this.visitorClass = visitorClass;
}
private Method findNullVisitorMethod() {
for (Class clazz = this.visitorClass; clazz != null; clazz = clazz.getSuperclass()) {
try {
return clazz.getDeclaredMethod(VISIT_NULL, (Class[])null);
}
catch (NoSuchMethodException e) {
}
}
return findDefaultVisitMethod();
}
private Method findDefaultVisitMethod() {
final Class[] args = {Object.class};
for (Class clazz = this.visitorClass; clazz != null; clazz = clazz.getSuperclass()) {
try {
return clazz.getDeclaredMethod(VISIT_METHOD, args);
}
catch (NoSuchMethodException e) {
}
}
if (logger.isWarnEnabled()) {
logger.warn("No default '" + VISIT_METHOD + "' method found. Returning ");
}
return null;
}
/**
* Gets a cached visitor method for the specified argument type.
*/
private Method getVisitMethod(Class argumentClass) {
return (Method) this.visitMethodCache.get(argumentClass);
}
/**
* Traverses class hierarchy looking for applicable visit() method.
*/
private Method findVisitMethod(Class rootArgumentType) {
if (rootArgumentType == Object.class) {
return null;
}
LinkedList classQueue = new LinkedList();
classQueue.addFirst(rootArgumentType);
while (!classQueue.isEmpty()) {
Class argumentType = (Class)classQueue.removeLast();
// Check for a visit method on the visitor class matching this
// argument type.
try {
if (logger.isDebugEnabled()) {
logger.debug("Looking for method " + VISIT_METHOD + "(" + argumentType + ")");
}
return findVisitMethod(this.visitorClass, argumentType);
}
catch (NoSuchMethodException e) {
// Queue up the argument super class if it's not of type Object.
if (!argumentType.isInterface() && (argumentType.getSuperclass() != Object.class)) {
classQueue.addFirst(argumentType.getSuperclass());
}
// Queue up argument's implemented interfaces.
Class[] interfaces = argumentType.getInterfaces();
for (int i = 0; i < interfaces.length; i++) {
classQueue.addFirst(interfaces[i]);
}
}
}
// No specific method found -> return the default.
return findDefaultVisitMethod();
}
private Method findVisitMethod(Class visitorClass, Class argumentType) throws NoSuchMethodException {
try {
return visitorClass.getDeclaredMethod(VISIT_METHOD, new Class[] {argumentType});
}
catch (NoSuchMethodException ex) {
// Try visitorClass superclasses.
if (visitorClass.getSuperclass() != Object.class) {
return findVisitMethod(visitorClass.getSuperclass(), argumentType);
}
else {
throw ex;
}
}
}
}
}