Java缓存Ehcache-Ehcache的Cache预热机制及代码实现（Cache Warming for multi-tier Caches）

Ehcache中Cache预热机制

Cache预热机制简介

Ehcache在程序启动的时候并不会立即去加载位于磁盘上的数据到内存，而是在数据被用到的时候去加载（lazy load）。因此在cache启动的时候，其内部没有数据。如果我们想在用到这些数据之前，它们全部被装载进内存，应该怎么做？

Ehcache提供了BootstrapCacheLoader机制来解决这个问题，在Cache被激活之前，它会得到运行。并且有两种模式：同步和异步。如果是同步模式，在CacheMana启动之前，加载便会完成；如果是异步模式，在CacheManager启动的时候，加载会在后台继续，而不是等到所需数据被需要的时候。

具体实现

我们只需要实现接口BootstrapCacheLoader定义自己的加载器MyBootstrapCacheLoader，继承BootstrapCacheLoaderFactory实现一个具体的加载工厂MyBootstrapCacheLoaderFactory即可实现数据的预热。

MyBootstrapCacheLoader负责实现怎么将数据加载进Cache，我们可以进行个性化的实现。MyBootstrapCacheLoaderFactory是一个具体的加载工厂，负责创建加载器实例，我们需要实现一些抽象方法。

下面看具体的代码实现（Java）。

MyBootstrapCacheLoader.java：

/** *  * Copyright (c) 2004-2014 All Rights Reserved. */package com..test.encache;import java.util.List;import net.sf.ehcache.CacheException;import net.sf.ehcache.Ehcache;import net.sf.ehcache.Element;import net.sf.ehcache.bootstrap.BootstrapCacheLoader;import org.slf4j.Logger;import org.slf4j.LoggerFactory;/** *  * @author  * @version $Id: CustomBootstrapCacheLoader.java, v 0.1 2014年10月18日 上午10:57:26  Exp $ */public class MyBootstrapCacheLoader implements BootstrapCacheLoader {    private static final Logger logger = LoggerFactory                                           .getLogger(MyBootstrapCacheLoaderFactory.class);    StatesDAO                   statesDAO;    boolean                     asynchronous;    /**      * @see net.sf.ehcache.bootstrap.BootstrapCacheLoader#load(net.sf.ehcache.Ehcache)     */    public void load(Ehcache cache) throws CacheException {        logger.info("load your cache with whatever you want....");        List keys = cache.getKeys();        for (int i = 0; i < keys.size(); i++) {            logger.info("keys->" + keys.get(i));        }        try {            List<String> dataList = getStatesDAO().findAllStates();            cache.put(new Element(CacheConstants.KEY_ARRAY[0], dataList.get(0)));            cache.put(new Element(CacheConstants.KEY_ARRAY[1], dataList.get(1)));        } catch (Exception e) {            // TODO Auto-generated catch block             e.printStackTrace();        }        logger.info("load end....");    }    /**      * @see net.sf.ehcache.bootstrap.BootstrapCacheLoader#isAsynchronous()     */    public boolean isAsynchronous() {        return asynchronous;    }    /**      * @see java.lang.Object#clone()     */    @Override    public Object clone() throws CloneNotSupportedException {        return super.clone();    }    public StatesDAO getStatesDAO() {        return statesDAO;    }    public void setStatesDAO(StatesDAO statesDAO) {        this.statesDAO = statesDAO;    }    /**     * Setter method for property <tt>asynchronous</tt>.     *      * @param asynchronous value to be assigned to property asynchronous     */    public void setAsynchronous(boolean asynchronous) {        this.asynchronous = asynchronous;    }}

MyBootstrapCacheLoaderFactory.java

/** *  * Copyright (c) 2004-2014 All Rights Reserved. */package com.test.encache;import java.util.Properties;import net.sf.ehcache.bootstrap.BootstrapCacheLoader;import net.sf.ehcache.bootstrap.BootstrapCacheLoaderFactory;import org.slf4j.Logger;import org.slf4j.LoggerFactory;import org.springframework.beans.factory.annotation.Autowired;/** * bootstrap cache loader *  * @author  * @version $Id: MyBootstrapCacheLoaderFactory.java, v 0.1 2014年10月17日 下午8:02:55  Exp $ */public class MyBootstrapCacheLoaderFactory extends BootstrapCacheLoaderFactory {    private final String ASYNCHRONOUS_PROPERTY_KEY = "ASYNCHRONOUS";    @Autowired    private StatesDAO    statesDAO;    public MyBootstrapCacheLoaderFactory() {        super();        // TODO Auto-generated constructor stub     }    private static final Logger logger = LoggerFactory                                           .getLogger(MyBootstrapCacheLoaderFactory.class);    @Override    public BootstrapCacheLoader createBootstrapCacheLoader(Properties properties) {        logger.info("MyBootstrapCacheLoaderFactory : create a BootstrapCacheLoader");        MyBootstrapCacheLoader loader = new MyBootstrapCacheLoader();        statesDAO = new StatesDAO();        loader.setStatesDAO(statesDAO);        loader.setAsynchronous(getAsyncFromProperty(properties));        return loader;    }    private boolean getAsyncFromProperty(Properties properties) {        String asynchronous = properties.getProperty(ASYNCHRONOUS_PROPERTY_KEY);        return Boolean.valueOf(asynchronous);    }}

使用了Cache的读取磁盘数据的方法在StatesDAO类中，对此我们只是进行了模拟，从数据库中读取数据。

StatesDAO.java

/** *  * Copyright (c) 2004-2014 All Rights Reserved. */package com.test.encache;import java.util.ArrayList;import java.util.List;import com.googlecode.ehcache.annotations.Cacheable;/** *  * @author  * @version $Id: StatesDAO.java, v 0.1 2014年10月17日 下午8:07:05  Exp $ */public class StatesDAO {    //annotation based caching and the name of cache should be defined in ehcache.xml.     @Cacheable(cacheName = "stateCache")    public List<String> findAllStates() {        List<String> dataList = new ArrayList<String>();        //your call to database that returns a list of objects          dataList.add("value1");        dataList.add("value2");        return dataList;    }}

Cache配置myehcache.xml：

<ehcache><diskStore path="D://localcache"/><cache name="stateCache" maxEntriesLocalHeap="10000" maxEntriesLocalDisk="1000" eternal="false" diskSpoolBufferSizeMB="20" timeToIdleSeconds="300" timeToLiveSeconds="600" memoryStoreEvictionPolicy="LFU" transactionalMode="off"><bootstrapCacheLoaderFactory class="com.test.encache.MyBootstrapCacheLoaderFactory"  properties="ASYNCHRONOUS=true"/></cache><cache name="stateCache2" maxEntriesLocalHeap="10000" maxEntriesLocalDisk="1000" eternal="false" diskSpoolBufferSizeMB="20" timeToIdleSeconds="300" timeToLiveSeconds="600" memoryStoreEvictionPolicy="LFU" transactionalMode="off"><bootstrapCacheLoaderFactory class="com.test.encache.MyBootstrapCacheLoaderFactory"  properties="ASYNCHRONOUS=false"/></cache></ehcache>

CacheManager配置ApplicationContext.xml：

<?xml version="1.0" encoding="UTF-8" ?><beans xmlns="http://www.springframework.org/schema/beans"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p"xmlns:context="http://www.springframework.org/schema/context"xmlns:aop="http://www.springframework.org/schema/aop" xmlns:tx="http://www.springframework.org/schema/tx"xmlns:ehcache="http://ehcache-spring-annotations.googlecode.com/svn/schema/ehcache-spring"xsi:schemaLocation="http://www.springframework.org/schema/beans        http://www.springframework.org/schema/beans/spring-beans-3.0.xsd       http://ehcache-spring-annotations.googlecode.com/svn/schema/ehcache-spring     http://ehcache-spring-annotations.googlecode.com/svn/schema/ehcache-spring/ehcache-spring-1.1.xsd"     default-autowire="byType">    <ehcache:annotation-driven cache-manager="ehCacheManager" /> <bean id="ehCacheManager" class="org.springframework.cache.ehcache.EhCacheManagerFactoryBean"> <property name="configLocation"> <value>src/config/myehcache.xml</value> </property></bean>     </beans>

最后是测试代码：BootstrapCacheLoaderTest.java：

/** *  * Copyright (c) 2004-2014 All Rights Reserved. */package com.test.encache;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.IOException;import java.util.Properties;import net.sf.ehcache.Cache;import net.sf.ehcache.CacheManager;import net.sf.ehcache.Element;import org.apache.log4j.PropertyConfigurator;import org.slf4j.Logger;import org.slf4j.LoggerFactory;import org.springframework.context.ApplicationContext;import org.springframework.context.support.FileSystemXmlApplicationContext;/** *  * @author  * @version $Id: BootstrapCacheLoader.java, v 0.1 2014年10月18日 上午11:31:06 Exp $ */public class BootstrapCacheLoaderTest {    private static String       log4jFileName      = "src/config/log4j.properties";    private static String       xmlFileName        = "src/config/ApplicationContext.xml";    private static String       ehcacheXmlFileName = "src/config/myehcache.xml";    private static final Logger logger             = LoggerFactory                                                       .getLogger(BootstrapCacheLoaderTest.class);    private static CacheManager ehCacheManager;    public static void main(String[] args) {        configProperty();        xmlLoad(ehcacheXmlFileName);        String[] cacheNamesStrings = ehCacheManager.getCacheNames();        logger.info("the number of caches in ehCacheManager : " + cacheNamesStrings.length);        Cache cache = ehCacheManager.getCache(CacheConstants.CACHE_NAME1);        Element element = cache.get(CacheConstants.KEY_ARRAY[0]);        logger.info("the element of key  " + CacheConstants.KEY_ARRAY[0] + " is " + element);    }    /**     * config properties     *      */    private static void configProperty() {        Properties properties = new Properties();        FileInputStream istream;        try {            istream = new FileInputStream(log4jFileName);            properties.load(istream);            istream.close();        } catch (FileNotFoundException e) {            logger.error("File not found", e);        } catch (IOException e) {            logger.error("load file erroe", e);        } finally {        }        //properties.setProperty("log4j.appender.file.File",logFile);         PropertyConfigurator.configure(properties);        logger.info("config properties success.");    }    private static void xmlLoad(String fileName) {        ApplicationContext ctx = new FileSystemXmlApplicationContext(xmlFileName);        ehCacheManager = (CacheManager) ctx.getBean("ehCacheManager");    }}

输出结果：
2014-10-18 15:17:45 INFO  BootstrapCacheLoaderTest:71 - config properties success.
2014-10-18 15:17:45 INFO  FileSystemXmlApplicationContext:513 - Refreshing org.springframework.context.support.FileSystemXmlApplicationContext@687b6889: startup date [Sat Oct 18 15:17:45 CST 2014]; root of context hierarchy
2014-10-18 15:17:45 INFO  XmlBeanDefinitionReader:316 - Loading XML bean definitions from file [D:\code\test\encache\src\config\ApplicationContext.xml]
2014-10-18 15:17:45 INFO  EhCacheManagerFactoryBean:136 - Initializing EhCache CacheManager
2014-10-18 15:17:46 INFO  MyBootstrapCacheLoaderFactory:38 - MyBootstrapCacheLoaderFactory : create a BootstrapCacheLoader
2014-10-18 15:17:46 INFO  MyBootstrapCacheLoaderFactory:38 - MyBootstrapCacheLoaderFactory : create a BootstrapCacheLoader
2014-10-18 15:17:46 INFO  MyBootstrapCacheLoaderFactory:34 - load your cache with whatever you want....
2014-10-18 15:17:46 INFO  MyBootstrapCacheLoaderFactory:51 - load end....
2014-10-18 15:17:46 INFO  MyBootstrapCacheLoaderFactory:34 - load your cache with whatever you want....
2014-10-18 15:17:46 INFO  MyBootstrapCacheLoaderFactory:51 - load end....
2014-10-18 15:17:46 INFO  BootstrapCacheLoaderTest:43 - the number of caches in ehCacheManager : 2
2014-10-18 15:17:46 INFO  BootstrapCacheLoaderTest:46 - the element of key  KEY1 is [ key = KEY1, value=value1, version=1, hitCount=1, CreationTime = 1413616666238, LastAccessTime = 1413616666302 ]

参考资料

Ehcache关于预热机制的官方文档

Load EhCache diskstore content into memory

How to load data to Ehcache when the application starts