package org.apache.ojb.broker.cache;

 /* Copyright 2003-2005 The Apache Software Foundation

  *

  * 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.

  */

 import org.apache.commons.lang.builder.ToStringBuilder;

 import org.apache.commons.lang.builder.ToStringStyle;

 import org.apache.ojb.broker.Identity;

 import org.apache.ojb.broker.PersistenceBroker;

 import java.lang.ref.SoftReference;

 import java.util.HashMap;

 import java.util.Map;

 import java.util.Properties;

 /**

  * Simple, flexible local {@link ObjectCache} implementation using a

  * {@link java.util.HashMap} to cache given objects.

  * <p>

  * The cache uses soft-references which allows objects (softly) referenced by

  * the cache to be reclaimed by the Java Garbage Collector when they are not

  * longer referenced elsewhere.

  * </p>

  * <p>

  * NOTE: Handle with care! If multiple PB instances are used (OJB standard behavior) you

  * will run into synchronization problems.

  * </p>

  * <p>

  * Implementation configuration properties:

  * </p>

  *

  * <table cellspacing="2" cellpadding="2" border="3" frame="box">

  * <tr>

  *     <td><strong>Property Key</strong></td>

  *     <td><strong>Property Values</strong></td>

  * </tr>

  * <tr>

  *     <td>timeout</td>

  *     <td>

  *          Lifetime of the cached objects in seconds.

  *          If expired the cached object was not returned

  *          on lookup call (and removed from cache).

  *    </td>

  * </tr>

  * </table>

  *

  * <br/>

  *

  * @author <a href="mailto:thma@apache.org">Thomas Mahler<a>

  * @author <a href="mailto:armin@codeAuLait.de">Armin Waibel</a>

  * @version $Id: ObjectCacheLocalDefaultImpl.java,v 1.1 2007-08-24 22:17:29 ewestfal Exp $

  */

 public class ObjectCacheLocalDefaultImpl implements ObjectCache

 {

     private static final String TIMEOUT = "timeout";

     /**

      * the hashtable holding all cached object

      */

     protected Map objectTable = new HashMap();

     /**

      * Timeout of the cached objects.

      */

     private long timeout = 1000 * 60 * 15;

     /**

      *

      */

     public ObjectCacheLocalDefaultImpl(PersistenceBroker broker, Properties prop)

     {

         timeout = prop == null ? timeout : ( Long.parseLong( prop.getProperty( TIMEOUT, "" + timeout ) ) )*1000;

     }

     /**

      * Clear ObjectCache. I.e. remove all entries for classes and objects.

      */

     public void clear()

     {

         objectTable.clear();

     }

     /**

      * Makes object persistent to the Objectcache.

      * I'm using soft-references to allow gc reclaim unused objects

      * even if they are still cached.

      */

     public void cache(Identity oid, Object obj)

     {

         if ((obj != null))

         {

             SoftReference ref = new SoftReference(new CacheEntry(obj));

             objectTable.put(oid, ref);

         }

     }

     public boolean cacheIfNew(Identity oid, Object obj)

     {

         if(objectTable.get(oid) == null)

         {

             cache(oid, obj);

             return true;

         }

         return false;

     }

     /**

      * Lookup object with Identity oid in objectTable.

      * Returns null if no matching id is found

      */

     public Object lookup(Identity oid)

     {

         CacheEntry entry = null;

         SoftReference ref = (SoftReference) objectTable.get(oid);

         if (ref != null)

         {

             entry = (CacheEntry) ref.get();

             if (entry == null || entry.lifetime < System.currentTimeMillis())

             {

                 objectTable.remove(oid);    // Soft-referenced Object reclaimed by GC

                 // timeout, so set null

                 entry = null;

             }

         }

         return entry != null ? entry.object : null;

     }

     /**

      * Removes an Object from the cache.

      */

     public void remove(Identity oid)

     {

         if (oid != null)

         {

             objectTable.remove(oid);

         }

     }

     public String toString()

     {

         ToStringBuilder buf = new ToStringBuilder(this, ToStringStyle.DEFAULT_STYLE);

         buf.append("Count of cached objects", objectTable.keySet().size());

         return buf.toString();

     }

     //-----------------------------------------------------------

     // inner class

     //-----------------------------------------------------------

     class CacheEntry

     {

         long lifetime;

         Object object;

         public CacheEntry(Object object)

         {

             this.object = object;

             lifetime = System.currentTimeMillis() + timeout;

         }

     }

 }