cache.java

Jive是基于JSP/JAVA技术构架的一个大型BBS论坛系统,这是Jive论坛2.6版本的源程序

/**
 * $RCSfile: Cache.java,v $
 * $Revision: 1.5 $
 * $Date: 2002/05/10 21:53:20 $
 *
 * Copyright (C) 1999-2002 CoolServlets, Inc. All rights reserved.
 *
 * This software is the proprietary information of CoolServlets, Inc.
 * Use is subject to license terms.
 */

package com.jivesoftware.util;

/**
 * General purpose cache. It stores objects associated with unique keys in
 * memory for fast access. All keys and values added to the cache must
 * implement the Serializable interface. Values may implement the Cacheable
 * interface, which allows the cache to determine object size much more quickly.
 * These restrictions allow a cache to never grow larger than a specified number
 * of bytes and to optionally be distributed over a cluster of servers.<p>
 *
 * If the cache does grow too large, objects will be removed such that those
 * that are accessed least frequently are removed first. Because expiration
 * happens automatically, the cache makes <b>no</b> gaurantee as to how long
 * an object will remain in cache after it is put in.<p>
 *
 * Optionally, a maximum lifetime for all objects can be specified. In that
 * case, objects will be deleted from cache after that amount of time, even
 * if they are frequently accessed. This feature is useful if objects put in
 * cache represent data that should be periodically refreshed; for example,
 * information from a database.<p>
 *
 * All cache operations are thread safe.<p>
 *
 * @see Cacheable
 * @author Matt Tucker
 */
public interface Cache extends java.util.Map {

    /**
     * Returns the name of the cache.
     *
     * @return the name of the cache.
     */
    String getName();

    /**
     * Returns the maximum size of the cache in bytes. If the cache grows
     * larger than the max size, the least frequently used items will be removed.
     *
     * @return the maximum size of the cache in bytes.
     */
    int getMaxCacheSize();

    /**
     * Sets the maximum size of the cache in bytes. If the cache grows
     * larger than the max size, the least frequently used items will be removed.
     *
     * @param maxSize the maximum size of the cache in bytes.
     */
    void setMaxCacheSize(int maxSize);

    /**
     * Returns the maximum number of milleseconds that any object can live
     * in cache. Once the specified number of milleseconds passes, the object
     * will be automatically expried from cache. If the max lifetime is set
     * to -1, then objects never expire.
     *
     * @return the maximum number of milleseconds before objects are expired.
     */
    long getMaxLifetime();

    /**
     * Sets the maximum number of milleseconds that any object can live
     * in cache. Once the specified number of milleseconds passes, the object
     * will be automatically expried from cache. If the max lifetime is set
     * to -1, then objects never expire.
     *
     * @param maxLifetime the maximum number of milleseconds before objects are expired.
     */
    void setMaxLifetime(long maxLifetime);

    /**
     * Returns the size of the cache contents in bytes. This value is only a
     * rough approximation, so cache users should expect that actual VM
     * memory used by the cache could be significantly higher than the value
     * reported by this method.
     *
     * @return the size of the cache contents in bytes.
     */
    int getCacheSize();

    /**
     * Returns the number of cache hits. A cache hit occurs every
     * time the get method is called and the cache contains the requested
     * object.<p>
     *
     * Keeping track of cache hits and misses lets one measure how efficient
     * the cache is; the higher the percentage of hits, the more efficient.
     *
     * @return the number of cache hits.
     */
    long getCacheHits();

    /**
     * Returns the number of cache misses. A cache miss occurs every
     * time the get method is called and the cache does not contain the
     * requested object.<p>
     *
     * Keeping track of cache hits and misses lets one measure how efficient
     * the cache is; the higher the percentage of hits, the more efficient.
     *
     * @return the number of cache hits.
     */
    long getCacheMisses();
}