cacheentry.java

来自「一个不错的cache」· Java 代码 · 共 312 行

/*
 * Copyright (c) 2002-2003 by OpenSymphony
 * All rights reserved.
 */
package com.opensymphony.oscache.base;

import com.opensymphony.oscache.web.filter.ResponseContent;

import java.io.Serializable;

import java.util.Collection;
import java.util.HashSet;
import java.util.Set;

/**
 * A CacheEntry instance represents one entry in the cache. It holds the object that
 * is being cached, along with a host of information about that entry such as the
 * cache key, the time it was cached, whether the entry has been flushed or not and
 * the groups it belongs to.
 *
 * @version        $Revision: 1.1 $
 * @author        <a href="mailto:[e-mail]">Mike Cannon-Brookes</a>
 * @author        <a href="mailto:[e-mail]">Todd Gochenour</a>
 * @author <a href="mailto:[e-mail]">Francois Beauregard</a>
 */
public class CacheEntry implements Serializable {
    /**
     * Default initialization value for the creation time and the last
     * update time. This is a placeholder that indicates the value has
     * not been set yet.
     */
    private static final byte NOT_YET = -1;

    /**
     * Specifying this as the refresh period for the
     * {@link #needsRefresh(int)} method will ensure
     * an entry does not become stale until it is
     * either explicitly flushed or a custom refresh
     * policy causes the entry to expire.
     */
    public static final int INDEFINITE_EXPIRY = -1;

    /**
     * The entry refresh policy object to use for this cache entry. This is optional.
     */
    private EntryRefreshPolicy policy = null;

    /**
     * The actual content that is being cached. Wherever possible this object
     * should be serializable. This allows <code>PersistenceListener</code>s
     * to serialize the cache entries to disk or database.
     */
    private Object content = null;

    /**
     * The set of cache groups that this cache entry belongs to, if any.
     */
    private Set groups = null;

    /**
     *  The unique cache key for this entry
     */
    private String key;

    /**
     * <code>true</code> if this entry was flushed
     */
    private boolean wasFlushed = false;

    /**
     * The time this entry was created.
     */
    private long created = NOT_YET;

    /**
     * The time this emtry was last updated.
     */
    private long lastUpdate = NOT_YET;

    /**
     * Construct a new CacheEntry using the key provided.
     *
     * @param key    The key of this CacheEntry
     */
    public CacheEntry(String key) {
        this(key, null);
    }

    /**
     * Construct a CacheEntry.
     *
     * @param key      The unique key for this <code>CacheEntry</code>.
     * @param policy   Object that implements refresh policy logic. This parameter
     * is optional.
     */
    public CacheEntry(String key, EntryRefreshPolicy policy) {
        this(key, policy, null);
    }

    /**
     * Construct a CacheEntry.
     *
     * @param key     The unique key for this <code>CacheEntry</code>.
     * @param policy  The object that implements the refresh policy logic. This
     * parameter is optional.
     * @param groups  The groups that this <code>CacheEntry</code> belongs to. This
     * parameter is optional.
     */
    public CacheEntry(String key, EntryRefreshPolicy policy, String[] groups) {
        this.key = key;

        if (groups != null) {
            this.groups = new HashSet(groups.length);

            for (int i = 0; i < groups.length; i++) {
                this.groups.add(groups[i]);
            }
        }

        this.policy = policy;
        this.created = System.currentTimeMillis();
    }

    /**
     * Sets the actual content that is being cached. Wherever possible this
     * object should be <code>Serializable</code>, however it is not an
     * absolute requirement when using a memory-only cache. Being <code>Serializable</code>
     * allows <code>PersistenceListener</code>s to serialize the cache entries to disk
     * or database.
     *
     * @param value The content to store in this CacheEntry.
     */
    public synchronized void setContent(Object value) {
        content = value;
        lastUpdate = System.currentTimeMillis();
        wasFlushed = false;
    }

    /**
     * Get the cached content from this CacheEntry.
     *
     * @return The content of this CacheEntry.
     */
    public Object getContent() {
        return content;
    }

    /**
     * Get the date this CacheEntry was created.
     *
     * @return The date this CacheEntry was created.
     */
    public long getCreated() {
        return created;
    }

    /**
     * Sets the cache groups for this entry.
     *
     * @param groups A string array containing all the group names
     */
    public synchronized void setGroups(String[] groups) {
        if (groups != null) {
            this.groups = new HashSet(groups.length);

            for (int i = 0; i < groups.length; i++) {
                this.groups.add(groups[i]);
            }
        } else {
            this.groups = null;
        }

        lastUpdate = System.currentTimeMillis();
    }

    /**
     * Sets the cache groups for this entry
     *
     * @param groups A collection containing all the group names
     */
    public void setGroups(Collection groups) {
        if (groups != null) {
            this.groups = new HashSet(groups);
        } else {
            this.groups = null;
        }

        lastUpdate = System.currentTimeMillis();
    }

    /**
     * Gets the cache groups that this cache entry belongs to.
     * These returned groups should be treated as immuatable.
     *
     * @return A set containing the names of all the groups that
     * this cache entry belongs to.
     */
    public Set getGroups() {
        return groups;
    }

    /**
     * Get the key of this CacheEntry
     *
     * @return The key of this CacheEntry
     */
    public String getKey() {
        return key;
    }

    /**
     * Set the date this CacheEntry was last updated.
     *
     * @param update The time (in milliseconds) this CacheEntry was last updated.
     */
    public void setLastUpdate(long update) {
        lastUpdate = update;
    }

    /**
     * Get the date this CacheEntry was last updated.
     *
     * @return The date this CacheEntry was last updated.
     */
    public long getLastUpdate() {
        return lastUpdate;
    }

    /**
     * Indicates whether this CacheEntry is a freshly created one and
     * has not yet been assigned content or placed in a cache.
     *
     * @return <code>true</code> if this entry is newly created
     */
    public boolean isNew() {
        return lastUpdate == NOT_YET;
    }

    /**
     * Get the size of the cache entry in bytes (roughly).<p>
     *
     * Currently this method only handles <code>String<code>s and
     * {@link ResponseContent} objects.
     *
     * @return The approximate size of the entry in bytes, or -1 if the
     * size could not be estimated.
     */
    public int getSize() {
        // a char is two bytes
        int size = (key.length() * 2) + 4;

        if (content.getClass() == String.class) {
            size += ((content.toString().length() * 2) + 4);
        } else if (content instanceof ResponseContent) {
            size += ((ResponseContent) content).getSize();
        } else {
            return -1;
        }

        //add created, lastUpdate, and wasFlushed field sizes (1, 8, and 8)
        return size + 17;
    }

    /**
     * Flush the entry from cache.
     * note that flushing the cache doesn't actually remove the cache contents
     * it just tells the CacheEntry that it needs a refresh next time it is asked
     * this is so that the content is still there for a <usecached />.
     */
    public void flush() {
        wasFlushed = true;
    }

    /**
     * Check if this CacheEntry needs to be refreshed.
     *
     * @param refreshPeriod The period of refresh (in seconds). Passing in
     * {@link #INDEFINITE_EXPIRY} will result in the content never becoming
     * stale unless it is explicitly flushed, or expired by a custom
     * {@link EntryRefreshPolicy}. Passing in 0 will always result in a
     * refresh being required.
     *
     * @return Whether or not this CacheEntry needs refreshing.
     */
    public boolean needsRefresh(int refreshPeriod) {
        boolean needsRefresh;

        // needs a refresh if it has never been updated
        if (lastUpdate == NOT_YET) {
            needsRefresh = true;
        }
        // Was it flushed from cache?
        else if (wasFlushed) {
            needsRefresh = true;
        } else if (refreshPeriod == 0) {
            needsRefresh = true;
        }
        // check what the policy has to say if there is one
        else if (policy != null) {
            needsRefresh = policy.needsRefresh(this);
        }
        // check if the last update + update period is in the past
        else if ((refreshPeriod >= 0) && (System.currentTimeMillis() >= (lastUpdate + (refreshPeriod * 1000L)))) {
            needsRefresh = true;
        } else {
            needsRefresh = false;
        }

        return needsRefresh;
    }
}