org.broadleafcommerce.common.extension.ExtensionManager.java Source code

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Here is the source code for org.broadleafcommerce.common.extension.ExtensionManager.java

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/*
 * #%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) {
                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;
        }
    }

}