org.apache.fulcrum.cache.impl.DefaultGlobalCacheService Maven / Gradle / Ivy
package org.apache.fulcrum.cache.impl;
/*
* 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.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.ObjectOutputStream;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ConcurrentHashMap;
import org.apache.avalon.framework.activity.Disposable;
import org.apache.avalon.framework.activity.Initializable;
import org.apache.avalon.framework.configuration.Configurable;
import org.apache.avalon.framework.configuration.Configuration;
import org.apache.avalon.framework.configuration.ConfigurationException;
import org.apache.avalon.framework.logger.AbstractLogEnabled;
import org.apache.avalon.framework.thread.ThreadSafe;
import org.apache.fulcrum.cache.CachedObject;
import org.apache.fulcrum.cache.GlobalCacheService;
import org.apache.fulcrum.cache.ObjectExpiredException;
import org.apache.fulcrum.cache.RefreshableCachedObject;
/**
* This Service functions as a Global Cache. A global cache is a good place to
* store items that you may need to access often but don't necessarily need (or
* want) to fetch from the database everytime. A good example would be a look up
* table of States that you store in a database and use throughout your
* application. Since information about States doesn't change very often, you
* could store this information in the Global Cache and decrease the overhead of
* hitting the database everytime you need State information.
*
* @author Dave Bryson
* @author Jon S. Stevens
* @author John Thorhauer
* @author Henning P. Schmiedehausen
* @author Eric Pugh
* @author Peter CourefreshableCachedObjectux
* @version $Id$
*/
public class DefaultGlobalCacheService extends AbstractLogEnabled implements
GlobalCacheService, Runnable, Configurable, Initializable, Disposable,
ThreadSafe
{
/**
* Initial size of hash table Value must be > 0. Default = 20
*/
public static final int DEFAULT_INITIAL_CACHE_SIZE = 20;
/**
* The property for the InitalCacheSize
*/
public static final String INITIAL_CACHE_SIZE = "cacheInitialSize";
/**
* The property for the Cache check frequency
*/
public static final String CACHE_CHECK_FREQUENCY = "cacheCheckFrequency";
/**
* Cache check frequency in Millis (1000 Millis = 1 second). Value must be >
* 0. Default = 5 seconds
*/
public static final long DEFAULT_CACHE_CHECK_FREQUENCY = 5000; // 5 seconds
/** The cache. */
protected transient ConcurrentHashMap> cache = null;
/**
* cacheCheckFrequency (default - 5 seconds)
*/
private transient long cacheCheckFrequency;
/**
* cacheInitialSize (default - 20)
*/
private transient int cacheInitialSize;
/** thread for removing stale items from the cache */
private transient Thread houseKeepingThread;
/** flag to stop the housekeeping thread when the component is disposed. */
private transient boolean continueThread;
public DefaultGlobalCacheService()
{
}
/**
* Get the Cache Check Frequency in milliseconds
*
* @return the time between two cache check runs in milliseconds
*/
public long getCacheCheckFrequency()
{
return this.cacheCheckFrequency;
}
/**
* Returns an item from the cache. /** Returns an item from the cache.
* RefreshableCachedObject will be refreshed if it is expired and not
* untouched.
*
* @param objectId
* The key of the stored object.
* @return The object from the cache.
* @throws ObjectExpiredException
* when either the object is not in the cache or it has
* expired.
*/
@Override
public CachedObject getObject(String objectId) throws ObjectExpiredException
{
@SuppressWarnings("unchecked")
final CachedObject cachedObject = (CachedObject) this.cache.get(objectId);
if (cachedObject == null)
{
// Not in the cache.
throw new ObjectExpiredException();
}
if (cachedObject.isStale())
{
if (cachedObject instanceof RefreshableCachedObject)
{
RefreshableCachedObject refreshableCachedObj = (RefreshableCachedObject) cachedObject;
if (refreshableCachedObj.isUntouched())
{
throw new ObjectExpiredException();
}
// Refresh Object
refreshableCachedObj.refresh();
if (refreshableCachedObj.isStale())
{
throw new ObjectExpiredException();
}
}
else
{
// Expired.
throw new ObjectExpiredException();
}
}
if (cachedObject instanceof RefreshableCachedObject)
{
// notify it that it's being accessed.
RefreshableCachedObject refreshableCachedObj = (RefreshableCachedObject) cachedObject;
refreshableCachedObj.touch();
}
return cachedObject;
}
/**
* Adds an object to the cache.
*
* @param objectId
* The key to store the object by.
* @param object
* The object to cache.
*/
@Override
public void addObject(final String objectId, final CachedObject object)
{
// If the cache already contains the key, remove it and add
// the fresh one.
if (this.cache.containsKey(objectId))
{
this.cache.remove(objectId);
}
this.cache.put(objectId, object);
}
/**
* Removes an object from the cache.
*
* @param objectId
* The String id for the object.
*/
@Override
public void removeObject(String objectId)
{
this.cache.remove(objectId);
}
/**
* Returns a copy of keys to objects in the cache as a list.
*
* Note that keys to expired objects are not returned.
*
* @return A List of String's representing the keys to
* objects in the cache.
*/
@Override
public List getKeys()
{
ArrayList keys = new ArrayList<>(this.cache.size());
for (String key : this.cache.keySet())
{
try
{
getObject(key);
}
catch (ObjectExpiredException oee)
{
// this is OK we just do not want this key
continue;
}
keys.add(key);
}
return keys;
}
/**
* Returns a copy of the non-expired CachedObjects in the cache as a list.
*
* @return A List of CachedObject objects held in the cache
*/
@Override
public List> getCachedObjects()
{
final ArrayList> objects = new ArrayList<>(this.cache.size());
for (String key : this.cache.keySet())
{
CachedObject cachedObject = null;
try
{
// only add non-null objects
cachedObject = getObject(key);
if ( cachedObject != null )
{
objects.add(cachedObject);
}
}
catch (ObjectExpiredException oee)
{
// this is OK we just do not want this object
continue;
}
}
return objects;
}
/**
* Circle through the cache and remove stale objects. Frequency is
* determined by the cacheCheckFrequency property.
*/
@Override
public void run()
{
while (this.continueThread && !Thread.currentThread().isInterrupted())
{
// Sleep for amount of time set in cacheCheckFrequency -
// default = 5 seconds.
synchronized (this)
{
try
{
wait(this.cacheCheckFrequency);
}
catch (InterruptedException exc)
{
// to be expected
}
}
clearCache();
}
}
/**
* Iterate through the cache and remove or refresh stale objects.
*/
public void clearCache()
{
List refreshThese = new ArrayList<>(20);
// Sync on this object so that other threads do not
// change the Hashtable while enumerating over it.
for (String key : this.cache.keySet())
{
final CachedObject cachedObject = this.cache.get(key);
if (cachedObject instanceof RefreshableCachedObject)
{
RefreshableCachedObject refreshableObject = (RefreshableCachedObject) cachedObject;
if (refreshableObject.isUntouched())
{
this.cache.remove(key);
}
else if (refreshableObject.isStale())
{
// to prolong holding the lock on this object
refreshThese.add(key);
}
}
else if (cachedObject.isStale())
{
this.cache.remove(key);
}
}
for (String key : refreshThese)
{
CachedObject cachedObject = this.cache.get(key);
RefreshableCachedObject refreshableCachedObject = (RefreshableCachedObject) cachedObject;
refreshableCachedObject.refresh();
}
}
/**
* Returns the number of objects currently stored in the cache
*
* @return int number of object in the cache
*/
@Override
public int getNumberOfObjects()
{
return this.cache.size();
}
/**
* Returns the current size of the cache.
*
* @return int representing current cache size in number of bytes
*/
@Override
public int getCacheSize() throws IOException
{
final ByteArrayOutputStream baos = new ByteArrayOutputStream();
final ObjectOutputStream out = new ObjectOutputStream(baos);
out.writeObject(this.cache);
out.flush();
//
// Subtract 4 bytes from the length, because the serialization
// magic number (2 bytes) and version number (2 bytes) are
// both written to the stream before the object
//
return baos.toByteArray().length - 4;
}
/**
* Flush the cache of all objects.
*/
@Override
public void flushCache()
{
this.cache.clear();
}
// ---------------- Avalon Lifecycle Methods ---------------------
/**
* Avalon component lifecycle method
*/
@Override
public void configure(Configuration conf) throws ConfigurationException
{
this.cacheCheckFrequency = conf.getAttributeAsLong(
CACHE_CHECK_FREQUENCY, DEFAULT_CACHE_CHECK_FREQUENCY);
this.cacheInitialSize = conf.getAttributeAsInteger(INITIAL_CACHE_SIZE,
DEFAULT_INITIAL_CACHE_SIZE);
}
/**
* Avalon component lifecycle method
*/
@Override
public void initialize() throws Exception
{
this.cache = new ConcurrentHashMap<>(this.cacheInitialSize);
// Start housekeeping thread.
this.continueThread = true;
this.houseKeepingThread = new Thread(this);
// Indicate that this is a system thread. JVM will quit only when
// there are no more active user threads. Settings threads spawned
// internally by Turbine as daemons allows commandline applications
// using Turbine to terminate in an orderly manner.
this.houseKeepingThread.setDaemon(true);
this.houseKeepingThread.start();
}
/**
* Avalon component lifecycle method
*/
@Override
public void dispose()
{
synchronized (this)
{
this.continueThread = false;
notifyAll();
}
}
}
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