ViewScopeBeanHolder

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 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.apache.myfaces.cdi.view;

import java.io.Serializable;
import java.util.Map;
import java.util.Random;
import java.util.concurrent.ConcurrentHashMap;
import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;
import javax.enterprise.context.SessionScoped;
import javax.enterprise.inject.spi.BeanManager;
import javax.faces.context.ExceptionHandler;
import javax.faces.context.ExternalContext;
import javax.faces.context.FacesContext;
import javax.inject.Inject;
import javax.servlet.ServletContext;
import org.apache.myfaces.context.ReleaseableExternalContext;
import org.apache.myfaces.context.servlet.StartupFacesContextImpl;
import org.apache.myfaces.context.servlet.StartupServletExternalContextImpl;
import org.apache.myfaces.shared.context.ExceptionHandlerImpl;

/**
 *
 * @author Leonardo Uribe
 */
@SessionScoped
public class ViewScopeBeanHolder implements Serializable
{
    /**
     * key: the windowId for the browser tab or window
     * value: the {@link ViewScopeContextualStorage} which holds all the
     * {@link javax.enterprise.inject.spi.Bean}s.
     */
    private Map<String, ViewScopeContextualStorage> storageMap;

    private static final Random RANDOM_GENERATOR = new Random();

    private static final String VIEW_SCOPE_PREFIX = "oam.view.SCOPE";

    public static final String VIEW_SCOPE_PREFIX_KEY = VIEW_SCOPE_PREFIX+".KEY";

    @Inject
    ApplicationContextBean applicationContextBean;

    public ViewScopeBeanHolder()
    {
    }

    @PostConstruct
    public void init()
    {
        storageMap = new ConcurrentHashMap<String, ViewScopeContextualStorage>();
        FacesContext facesContext = FacesContext.getCurrentInstance();
        facesContext.getExternalContext().getSessionMap().put(VIEW_SCOPE_PREFIX_KEY,
            1);
    }

    /**
     * This method will return the ViewScopeContextualStorage or create a new one
     * if no one is yet assigned to the current windowId.
     * @param beanManager we need the CDI {@link BeanManager} for serialisation.
     * @param windowId the windowId for the current browser tab or window.
     */
    public ViewScopeContextualStorage getContextualStorage(
        BeanManager beanManager, String viewScopeId)
    {
        ViewScopeContextualStorage contextualStorage = storageMap.get(viewScopeId);
        if (contextualStorage == null)
        {
            synchronized (this)
            {
                contextualStorage = storageMap.get(viewScopeId);
                if (contextualStorage == null)
                {
                    contextualStorage = new ViewScopeContextualStorage(beanManager);
                    storageMap.put(viewScopeId, contextualStorage);
                }
            }
        }
        return contextualStorage;
    }

    public Map<String, ViewScopeContextualStorage> getStorageMap()
    {
        return storageMap;
    }

    /**
     *
     * This method will replace the storageMap and with
     * a new empty one.
     * This method can be used to properly destroy the WindowBeanHolder beans
     * without having to sync heavily. Any
     * {@link javax.enterprise.inject.spi.Bean#destroy(Object, javax.enterprise.context.spi.CreationalContext)}
     * should be performed on the returned old storage map.
     * @return the old storageMap.
     */
    public Map<String, ViewScopeContextualStorage> forceNewStorage()
    {
        Map<String, ViewScopeContextualStorage> oldStorageMap = storageMap;
        storageMap = new ConcurrentHashMap<String, ViewScopeContextualStorage>();
        return oldStorageMap;
    }

    /**
     * This method properly destroys all current &#064;WindowScoped beans
     * of the active session and also prepares the storage for new beans.
     * It will automatically get called when the session context closes
     * but can also get invoked manually, e.g. if a user likes to get rid
     * of all it's &#064;ViewScoped beans.
     */
    //@PreDestroy
    public void destroyBeans()
    {
        // we replace the old windowBeanHolder beans with a new storage Map
        // an afterwards destroy the old Beans without having to care about any syncs.
        // This behavior also helps as a check to avoid destroy the same beans twice.
        Map<String, ViewScopeContextualStorage> oldWindowContextStorages = forceNewStorage();

        for (ViewScopeContextualStorage contextualStorage : oldWindowContextStorages.values())
        {
            ViewScopeContextImpl.destroyAllActive(contextualStorage);
        }
    }

    public void destroyBeans(String viewScopeId)
    {
        ViewScopeContextualStorage contextualStorage = storageMap.get(viewScopeId);
        if (contextualStorage != null)
        {
            try
            {
                FacesContext facesContext = FacesContext.getCurrentInstance();
                if (facesContext == null &&
                    applicationContextBean.getServletContext() != null)
                {
                    try
                    {
                        ServletContext servletContext = applicationContextBean.getServletContext();
                        ExternalContext externalContext = new StartupServletExternalContextImpl(servletContext, false);
                        ExceptionHandler exceptionHandler = new ExceptionHandlerImpl();
                        facesContext = new StartupFacesContextImpl(externalContext,
                                (ReleaseableExternalContext) externalContext, exceptionHandler, false);
                        ViewScopeContextImpl.destroyAllActive(contextualStorage, facesContext);
                    }
                    finally
                    {
                        facesContext.release();
                    }
                }
                else
                {
                    ViewScopeContextImpl.destroyAllActive(contextualStorage, facesContext);
                }
            }
            finally
            {
                //remove the viewScopeId to prevent memory leak
                storageMap.remove(viewScopeId);
            }
        }
    }

    @PreDestroy
    public void destroyBeansOnPreDestroy()
    {
        // After some testing done two things are clear:
        // 1. jetty +  weld call @PreDestroy at the end of the request
        // 2. use a HttpServletListener in tomcat + owb does not work, because
        //    CDI listener is executed first.
        // So we need a mixed approach using both a listener and @PreDestroy annotations.
        // When the first one in being called replace the storages with a new map
        // and call PreDestroy, when the second one is called, it founds an empty map
        // and the process stops. A hack to get ServletContext from CDI is required to
        // provide a valid FacesContext instance.
        Map<String, ViewScopeContextualStorage> oldWindowContextStorages = forceNewStorage();
        if (!oldWindowContextStorages.isEmpty())
        {
            FacesContext facesContext = FacesContext.getCurrentInstance();
            if (facesContext == null &&
                applicationContextBean.getServletContext() != null)
            {
                try
                {
                    ServletContext servletContext = applicationContextBean.getServletContext();
                    ExternalContext externalContext = new StartupServletExternalContextImpl(servletContext, false);
                    ExceptionHandler exceptionHandler = new ExceptionHandlerImpl();
                    facesContext = new StartupFacesContextImpl(externalContext,
                            (ReleaseableExternalContext) externalContext, exceptionHandler, false);
                    for (ViewScopeContextualStorage contextualStorage : oldWindowContextStorages.values())
                    {
                        ViewScopeContextImpl.destroyAllActive(contextualStorage, facesContext);
                    }
                }
                finally
                {
                    facesContext.release();
                }
            }
            else
            {
                for (ViewScopeContextualStorage contextualStorage : oldWindowContextStorages.values())
                {
                    ViewScopeContextImpl.destroyAllActive(contextualStorage);
                }
            }
        }
    }

    public String generateUniqueViewScopeId()
    {
        // To ensure uniqueness we just use a random generator and we check
        // if the key is already used.
        String key;
        do
        {
            key = Integer.toString(RANDOM_GENERATOR.nextInt());
        } while (storageMap.containsKey(key));
        return key;
    }

}