org.apache.wicket.request.resource.caching.version.CachingResourceVersion.java Source code

Introduction

Here is the source code for org.apache.wicket.request.resource.caching.version.CachingResourceVersion.java

Source

/*
 * 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.
 */
package org.apache.wicket.request.resource.caching.version;

import java.io.Serializable;
import java.util.Collections;
import java.util.Map;
import java.util.regex.Pattern;

import org.apache.wicket.request.resource.caching.IStaticCacheableResource;
import org.apache.wicket.util.collections.MostRecentlyUsedMap;
import org.apache.wicket.util.lang.Args;

/**
 * Caches the results of a delegating {@link IResourceVersion} instance
 * in a member variable. The cache will be valid for the lifetime of 
 * this instance. It will expire the oldest entries if the maximum number 
 * of entries is exceeded.
 * 
 * @autor Peter Ertl
 * 
 * @since 1.5
 */
public class CachingResourceVersion implements IResourceVersion {
    /**
     * default maximum entries in cache
     */
    private static final int DEFAULT_MAX_CACHE_ENTRIES = 5000;

    /**
     * null value replacement holder for storing <code>null</code> in the map 
     */
    private static final String NULL_VALUE = "null";

    /**
     * delegating resource version provider
     */
    private final IResourceVersion delegate;

    /**
     * cache for resource versions
     */
    private final Map<Serializable, String> cache;

    /**
     * create version cache
     * <p/>
     * the cache will accept up to {@value #DEFAULT_MAX_CACHE_ENTRIES} before 
     * evicting the oldest entries.
     * 
     * @param delegate
     *           delegating resource version provider
     */
    public CachingResourceVersion(IResourceVersion delegate) {
        this(delegate, DEFAULT_MAX_CACHE_ENTRIES);
    }

    /**
     * create version cache
     * <p/>
     * the cache will accept a maximum number of entries specified
     * by <code>maxEntries</code> before evicting the oldest entries.
     * 
     * @param delegate
     *          resource version provider
     * @param maxEntries
     *          maximum number of cache entries
     */
    public CachingResourceVersion(IResourceVersion delegate, int maxEntries) {
        if (maxEntries < 1) {
            throw new IllegalArgumentException("maxEntries must be greater than zero");
        }

        this.delegate = Args.notNull(delegate, "delegate");
        this.cache = Collections.synchronizedMap(new MostRecentlyUsedMap<Serializable, String>(maxEntries));
    }

    @Override
    public String getVersion(IStaticCacheableResource resource) {
        // get unique cache key for resource reference
        final Serializable key = resource.getCacheKey();

        // if key can not be determined do not cache
        if (key == null) {
            return null;
        }

        // lookup version in cache
        String version = cache.get(key);

        // if not found
        if (version == null) {
            // get version from delegate
            version = delegate.getVersion(resource);

            // replace null values with holder
            if (version == null) {
                version = NULL_VALUE;
            }
            // update cache
            cache.put(key, version);
        }

        //noinspection StringEquality
        if (version == NULL_VALUE) {
            // replace holder with null value
            return null;
        }

        // return version string
        return version;
    }

    @Override
    public Pattern getVersionPattern() {
        return delegate.getVersionPattern();
    }

    /**
     * remove cacheable resource from cache
     * 
     * @param resource 
     *           cacheable resource
     */
    public void invalidate(IStaticCacheableResource resource) {
        // get cache key for resource reference
        final Serializable key = Args.notNull(resource, "resource").getCacheKey();

        // if key is available purge cache entry
        if (key != null) {
            cache.remove(key);
        }
    }

    public void invalidateAll() {
        cache.clear();
    }
}