001/*
002 * (C) Copyright 2006-2011 Nuxeo SA (http://nuxeo.com/) and others.
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 *     http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 *
016 * Contributors:
017 *     bstefanescu
018 *
019 * $Id$
020 */
021
022package org.nuxeo.ecm.core.repository;
023
024import org.nuxeo.ecm.core.api.CoreSession;
025
026/**
027 * A repository initialization handler is responsible for initializing a repository content.
028 * <p>
029 * The handler is called each time a repository is opened in a JVM session. This can be used to create a default
030 * structure for the repository.
031 * <p>
032 * To register a repository initializer <code>MyInitHandler</code> you should do:
033 * <p>
034 * <code>RepositoryInitializationHandler.setInstance(new MyInitHandler());</code>
035 * <p>
036 * If you want to create an initialization chain you can implement to delegate to the parent handle the default
037 * initialization and then to do your specific initialization stuff
038 *
039 * <pre>
040 * <code>
041 * RepositoryInitializationHandler parentHandler = RepositoryInitializationHandler.getInstance();
042 * MyInitHandler myHandler = new MyInitHandler(parentHandler);
043 * RepositoryInitializationHandler.setInstance(myHandler);
044 * ...
045 * class MyHandler extends RepositoryInitializationHandler {
046 *      ...
047 *      public initializeRepository(CoreSession session) {
048 *        if (parentHandler != null) parentHandler.initializeRepository(session);
049 *        // do my own initialization here
050 *        ...
051 *      }
052 *      ...
053 * }
054 * </code>
055 * </pre>
056 * <p>
057 * <b>Important Note:</b> Use the given session to initialize the repository. Do not create other repository sessions
058 * when initializing the repository to avoid dead locks.
059 *
060 * @author <a href="mailto:bs@nuxeo.com">Bogdan Stefanescu</a>
061 */
062public abstract class RepositoryInitializationHandler {
063
064    protected static RepositoryInitializationHandler instance;
065
066    public static RepositoryInitializationHandler getInstance() {
067        return instance;
068    }
069
070    /**
071     * The parent handler if any otherwise null
072     */
073    protected RepositoryInitializationHandler previous;
074
075    /**
076     * The next handler in the chain if any or null otherwise
077     */
078    protected RepositoryInitializationHandler next;
079
080    public abstract void doInitializeRepository(CoreSession session);
081
082    /**
083     * Must be implemented by custom initializers.
084     *
085     * @param session the current session
086     */
087    public void initializeRepository(CoreSession session) {
088        synchronized (RepositoryInitializationHandler.class) {
089            if (previous != null) {
090                previous.initializeRepository(session);
091            }
092            doInitializeRepository(session);
093        }
094    }
095
096    public void install() {
097        synchronized (RepositoryInitializationHandler.class) {
098            previous = instance;
099            if (previous != null) {
100                previous.next = this;
101            }
102            instance = this;
103        }
104    }
105
106    public void uninstall() {
107        synchronized (RepositoryInitializationHandler.class) {
108            if (previous != null) {
109                previous.next = next;
110            }
111            if (next != null) {
112                next.previous = previous;
113            }
114            if (instance == this) {
115                instance = previous;
116            }
117        }
118    }
119
120    public RepositoryInitializationHandler getPrevious() {
121        return previous;
122    }
123
124    public RepositoryInitializationHandler getNext() {
125        return next;
126    }
127
128}