/*
* #%L
* BroadleafCommerce Common Libraries
* %%
* Copyright (C) 2009 - 2013 Broadleaf Commerce
* %%
* 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.
* #L%
*/
package org.broadleafcommerce.common.extension;
import org.apache.commons.beanutils.BeanComparator;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
/**
* The ExtensionManager pattern is intended for out of box components to be extended by Broadleaf modules.
*
* Each component that needs an extension should define an interface which is a descendant of ExtensionHandler.
* The concrete ExtensionManager class will utilize that interface as a parameter (e.g. T below).
*
* The default extension manager pattern loops through all handlers and examines their {@link ExtensionResultStatusType}
* to determine whether or not to continue with other handlers.
*
* @author bpolster
*
* @param <T>
*/
public abstract class ExtensionManager<T extends ExtensionHandler> implements InvocationHandler {
protected boolean handlersSorted = false;
protected static String LOCK_OBJECT = new String("EM_LOCK");
protected T extensionHandler;
protected List<T> handlers = new ArrayList<T>();
/**
* Should take in a className that matches the ExtensionHandler interface being managed.
* @param className
*/
@SuppressWarnings("unchecked")
public ExtensionManager(Class<T> _clazz) {
extensionHandler = (T) Proxy.newProxyInstance(_clazz.getClassLoader(),
new Class[] { _clazz },
this);
}
public T getProxy() {
return extensionHandler;
}
/**
* If you are attempting to register a handler with this manager and are invoking this outside of an {@link ExtensionManager}
* subclass, consider using {@link #registerHandler(ExtensionHandler)} instead.
*
* While the sorting of the handlers prior to their return is thread safe, adding directly to this list is not.
*
* @return a list of handlers sorted by their priority
* @see {@link #registerHandler(ExtensionHandler)}
*/
@SuppressWarnings({ "unchecked", "rawtypes" })
public List<T> getHandlers() {
synchronized (LOCK_OBJECT) {
if (!handlersSorted) {
if (!handlersSorted) {
Comparator fieldCompare = new BeanComparator("priority");
Collections.sort(handlers, fieldCompare);
handlersSorted = true;
}
}
return handlers;
}
}
/**
* Intended to be invoked from the extension handlers themselves. This will add the given handler to this manager's list of
* handlers. This also checks to ensure that the handler has not been already registered with this {@link ExtensionManager}
* by checking the class names of the already-added handlers.
*
* This method is thread safe.
*
* @param handler the handler to register with this extension manager
* @return true if the handler was successfully registered, false if this handler was already contained in the list of
* handlers for this manager
*/
public boolean registerHandler(T handler) {
synchronized (LOCK_OBJECT) {
boolean add = true;
for (T item : this.handlers) {
if (item.getClass().equals(handler.getClass())) {
add = false;
}
}
if (add) {
this.handlers.add(handler);
handlersSorted = false;
}
return add;
}
}
public void setHandlers(List<T> handlers) {
this.handlers = handlers;
}
/**
* Utility method that is useful for determining whether or not an ExtensionManager implementation
* should continue after processing a ExtensionHandler call.
*
* By default, returns true for CONTINUE
*
* @return
*/
public boolean shouldContinue(ExtensionResultStatusType result, ExtensionHandler handler,
Method method, Object[] args) {
if (result != null) {
if (ExtensionResultStatusType.HANDLED_STOP.equals(result)) {
return false;
}
if (ExtensionResultStatusType.HANDLED.equals(result) && ! continueOnHandled()) {
return false;
}
}
return true;
}
/**
* Returns whether or not this extension manager continues on {@link ExtensionResultStatusType}.HANDLED.
*
* @return
*/
public boolean continueOnHandled() {
return false;
}
/**
* {@link ExtensionManager}s don't really need a priority but they pick up this property due to the
* fact that we want them to implement the same interface <T> as the handlers they are managing.
*
* @return
*/
public int getPriority() {
throw new UnsupportedOperationException();
}
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
boolean notHandled = true;
for (ExtensionHandler handler : getHandlers()) {
try {
if (handler.isEnabled()) {
ExtensionResultStatusType result = (ExtensionResultStatusType) method.invoke(handler, args);
if (!ExtensionResultStatusType.NOT_HANDLED.equals(result)) {
notHandled = false;
}
if (!shouldContinue(result, handler, method, args)) {
break;
}
}
} catch (InvocationTargetException e) {
throw e.getCause();
}
}
if (notHandled) {
return ExtensionResultStatusType.NOT_HANDLED;
} else {
return ExtensionResultStatusType.HANDLED;
}
}
}