ThreadLocalStorageImpl.java

package org.apache.fulcrum.yaafi.framework.tls;

/*
 * 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.
 */

import java.util.HashMap;
import java.util.Map;

/**
 * Implementation of {@link org.apache.fulcrum.yaafi.framework.tls.ThreadLocalStorage}.
 *
 * The code was pasted from the Hivemnind container written by
 * Howard Lewis Ship and Harish Krishnaswamy
 *
 * @author <a href="mailto:siegfried.goeschl@it20one.at">Siegfried Goeschl</a>
 */

public class ThreadLocalStorageImpl implements ThreadLocalStorage
{
    private static final String INITIALIZED_KEY =
        "$org.apache.fulcrum.yaafi.framework.tls.ThreadLocalStorageImpl#initialized$";

    private CleanableThreadLocal local = new CleanableThreadLocal();

    private static class CleanableThreadLocal extends ThreadLocal<Object>
    {
        /**
         * <p>
         * Intializes the variable with a HashMap containing a single Boolean flag to denote the
         * initialization of the variable.
         */
        protected Object initialValue()
        {
            // NOTE: This is a workaround to circumvent the ThreadLocal behavior.
            // It would be easier if the implementation of ThreadLocal.get() checked for
            // the existence of the thread local map, after initialValue() is evaluated,
            // and used it instead of creating a new map always after initialization (possibly
            // overwriting any variables created from within ThreadLocal.initialValue()).

            Map<String, Boolean> map = new HashMap<String, Boolean>();
            map.put(INITIALIZED_KEY, Boolean.TRUE);

            return map;
        }
    }

    /**
     * Gets the thread local variable and registers the listener with ThreadEventNotifier
     * if the thread local variable has been initialized. The registration cannot be done from
     * within {@link CleanableThreadLocal#initialValue()} because the notifier's thread local
     * variable will be overwritten and the listeners for the thread will be lost.
     */
    private Map<String, Object> getThreadLocalVariable()
    {
        Map<String, Object> map = (Map<String, Object>) local.get();
        return map;
    }

    public Object get(String key)
    {
        Map<String, Object> map = getThreadLocalVariable();
        return map.get(key);
    }

    public void put(String key, Object value)
    {
        Map<String, Object> map = getThreadLocalVariable();
        map.put(key, value);
    }

    public boolean containsKey(String key)
    {
        Map<String, Object> map = getThreadLocalVariable();
        return map.containsKey(key);
    }

    public void clear()
    {
        Map<?, ?> map = (Map<?, ?>) local.get();
        if (map != null)
        {
            map.clear();
        }
    }
}