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