Java tutorial
/** * 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.apex.malhar.lib.db.cache; import java.io.IOException; import java.util.List; import java.util.Map; import java.util.Set; import java.util.concurrent.Executors; import java.util.concurrent.ScheduledExecutorService; import java.util.concurrent.TimeUnit; import javax.validation.constraints.Min; import javax.validation.constraints.NotNull; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import com.google.common.cache.Cache; import com.google.common.cache.CacheBuilder; import com.google.common.collect.Lists; import com.datatorrent.api.Component; /** * A {@link CacheManager.Primary} which keeps key/value pairs in memory.<br/> * * Properties of the cache store:<br/> * <ul> * <li>Transient: It is not checkpointed.</li> * <li>Max Cache Size: it starts evicting entries before this limit is exceeded.</li> * <li>Entry expiry time: the entries epire after the specified duration.</li> * <li>Cache cleanup interval: the interval at which the cache is cleaned up of expired entries periodically.</li> * </ul> * * @since 0.9.2 */ public class CacheStore implements CacheManager.Primary, Component<CacheManager.CacheContext> { @Min(0) protected long maxCacheSize = 2000; @Min(0) protected long entryExpiryDurationInMillis = 60000; //1 minute @Min(0) protected long cacheCleanupIntervalInMillis = 60500; //.5 seconds after entries are expired @NotNull protected ExpiryType entryExpiryStrategy = ExpiryType.EXPIRE_AFTER_ACCESS; private transient ScheduledExecutorService cleanupScheduler; private transient Cache<Object, Object> cache; private transient boolean open; private transient int numInitCacheLines = -1; private static final Logger logger = LoggerFactory.getLogger(CacheStore.class); @Override public void put(Object key, Object value) { cache.put(key, value); } @Override public Set<Object> getKeys() { return cache.asMap().keySet(); } @Override public void putAll(Map<Object, Object> data) { cache.asMap().putAll(data); } @Override public void remove(Object key) { cache.invalidate(key); } @Override public Object get(Object key) { return cache.getIfPresent(key); } @Override public List<Object> getAll(List<Object> keys) { List<Object> values = Lists.newArrayList(); for (Object key : keys) { values.add(cache.getIfPresent(key)); } return values; } @Override public void connect() throws IOException { open = true; if (numInitCacheLines > maxCacheSize) { logger.warn("numInitCacheLines = {} is greater than maxCacheSize = {}, maxCacheSize was set to {}", numInitCacheLines, maxCacheSize, numInitCacheLines); maxCacheSize = numInitCacheLines; } CacheBuilder<Object, Object> cacheBuilder = CacheBuilder.newBuilder(); cacheBuilder.maximumSize(maxCacheSize); if (entryExpiryStrategy == ExpiryType.EXPIRE_AFTER_ACCESS) { cacheBuilder.expireAfterAccess(entryExpiryDurationInMillis, TimeUnit.MILLISECONDS); } else if (entryExpiryStrategy == ExpiryType.EXPIRE_AFTER_WRITE) { cacheBuilder.expireAfterWrite(entryExpiryDurationInMillis, TimeUnit.MILLISECONDS); } cache = cacheBuilder.build(); if (entryExpiryStrategy == ExpiryType.NO_EVICTION) { return; } this.cleanupScheduler = Executors.newScheduledThreadPool(1); cleanupScheduler.scheduleAtFixedRate(new Runnable() { @Override public void run() { cache.cleanUp(); } }, cacheCleanupIntervalInMillis, cacheCleanupIntervalInMillis, TimeUnit.MILLISECONDS); } @Override public boolean isConnected() { return open; } @Override public void disconnect() throws IOException { open = false; if (cleanupScheduler != null) { cleanupScheduler.shutdown(); } } /** * Sets the max size of cache. * * @param maxCacheSize the max size of cache in memory. */ public void setMaxCacheSize(long maxCacheSize) { this.maxCacheSize = maxCacheSize; } /** * Sets the cache entry expiry strategy. * * @param expiryType the cache entry expiry strategy. */ public void setEntryExpiryStrategy(ExpiryType expiryType) { this.entryExpiryStrategy = expiryType; } /** * Sets the expiry time of cache entries in millis. * * @param durationInMillis the duration after which a cache entry is expired. */ public void setEntryExpiryDurationInMillis(long durationInMillis) { this.entryExpiryDurationInMillis = durationInMillis; } /** * Sets the interval at which cache is cleaned up regularly. * * @param durationInMillis the duration after which cache is cleaned up regularly. */ public void setCacheCleanupInMillis(long durationInMillis) { this.cacheCleanupIntervalInMillis = durationInMillis; } /** * Callback to give the component a chance to perform tasks required as part of setting itself up. * This callback is made exactly once during the operator lifetime. * * @param context - CacheContext with AttributeMap passed by CacheManager */ @Override public void setup(CacheManager.CacheContext context) { if (context != null) { numInitCacheLines = context.getValue(CacheManager.CacheContext.NUM_INIT_CACHED_LINES_ATTR); if (context.getValue(CacheManager.CacheContext.READ_ONLY_ATTR)) { entryExpiryStrategy = ExpiryType.NO_EVICTION; } } } @Override public void teardown() { } /** * Strategies for time-based expiration of entries. */ public enum ExpiryType { /** * Only expire the entries after the specified duration has passed since the entry was last accessed by a read * or a write. */ EXPIRE_AFTER_ACCESS, /** * Expire the entries after the specified duration has passed since the entry was created, or the most recent * replacement of the value. */ EXPIRE_AFTER_WRITE, /** * Entries never expire. No eviction will be set in cache builder and no cache cleaning will be scheduled. */ NO_EVICTION } }