querycache.java

用Java实现的23个常用设计模式源代码

//$Id: QueryCache.java,v 1.1.2.5 2003/11/09 12:19:07 oneovthafew Exp $
package net.sf.hibernate.cache;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;
import java.util.Properties;
import java.util.Set;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import net.sf.hibernate.HibernateException;
import net.sf.hibernate.engine.SessionImplementor;
import net.sf.hibernate.type.Type;
import net.sf.hibernate.type.TypeFactory;

/**
 * A cache for query result sets. The transactional semantics are necessarily
 * less strict than the semantics of an item cache. Note that the actual
 * entities in the result set are not kept in this cache, only their ids.
 * @author Gavin King
 */
public class QueryCache {
	
	private static final Log log = LogFactory.getLog(QueryCache.class);
	
	private Cache queryCache;
	private UpdateTimestampsCache updateTimestampsCache;
	private final String regionName;
	
	public void clear() throws CacheException {
		queryCache.clear();
	}
	
	public QueryCache(CacheProvider provider, Properties props, UpdateTimestampsCache updateTimestampsCache, String regionName) 
	throws HibernateException {
		if (regionName==null) regionName = QueryCache.class.getName();
		log.info("starting query cache at region: " + regionName);
		this.queryCache = provider.buildCache(regionName, props);
		this.updateTimestampsCache = updateTimestampsCache;
		this.regionName = regionName;
	}
	
	public void put(QueryKey key, Type[] returnTypes, List result, SessionImplementor session) throws HibernateException {
		if ( log.isDebugEnabled() ) log.debug("caching query results in region: " + regionName);
		List cacheable = new ArrayList( result.size()+1 );
		cacheable.add( new Long( session.getTimestamp() ) );
		for ( int i=0; i<result.size(); i++ ) {
			if ( returnTypes.length==1 ) {
				cacheable.add( returnTypes[0].disassemble( result.get(i), session ) );
			}
			else {
				cacheable.add( TypeFactory.disassemble( (Object[]) result.get(i), returnTypes, session ) );
			}
		}
		queryCache.put( key, cacheable );
	}

	public List get(QueryKey key, Type[] returnTypes, Set spaces, SessionImplementor session) throws HibernateException {
		if ( log.isDebugEnabled() ) log.debug("checking cached query results in region: " + regionName);
		List cacheable = (List) queryCache.get(key);
		if (cacheable==null) {
			log.debug("query results were not found in cache");
			return null;
		}
		List result = new ArrayList( cacheable.size()-1 );
		Long timestamp = (Long) cacheable.get(0);
		if ( !updateTimestampsCache.isUpToDate(spaces, timestamp) ) {
			log.debug("cached query results were not up to date");
			return null;
		}
		log.debug("returning cached query results");
		for ( int i=1; i<cacheable.size(); i++ ) {
			if ( returnTypes.length==1 ) {
				result.add( returnTypes[0].assemble( (Serializable) cacheable.get(i), session, null ) );
			}
			else {
				result.add( TypeFactory.assemble( (Serializable[]) cacheable.get(i), returnTypes, session, null ) );
			}
		}
		return result;
	}

	public void destroy() {
		try {
			queryCache.destroy();
		}
		catch (Exception e) {
			log.warn("could not destroy query cache: " + regionName, e);
		}
	}

}