Spring仅仅是提供了对缓存的支持，但它并没有任何的缓存功能的实现，spring使用的是第三方的缓存框架来实现缓存的功能。其中，spring对EHCache提供了很好的支持。
在介绍Spring的缓存配置之前，我们先看一下EHCache是如何配置。
<?xml version="1.0" encoding="UTF-8" ?> <ehcache> <!-- 定义默认的缓存区，如果在未指定缓存区时，默认使用该缓存区 --> <defaultCache maxElementsInMemory="500" eternal="true" overflowToDisk="false" memoryStoreEvictionPolicy="LFU"> </defaultCache> <!-- 定义名字为"dao.select"的缓存区 --> <cache name="dao.select" maxElementsInMemory="500" eternal="true" overflowToDisk="false" memoryStoreEvictionPolicy="LFU" /> </ehcache>
由于Spring的缓存机制是基于Spring的AOP，那么在Spring Cache中应该存在着一个Advice。没错，在Spring Cache中的Advice是存在的，它就是org.springframework.cache.Cache。我们看一下它的接口定义：
/* * Copyright 2002-2011 the original author or authors. * * Licensed 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.springframework.cache; /** * Interface that defines the common cache operations. * * <b>Note:</b> Due to the generic use of caching, it is recommended that * implementations allow storage of <tt>null</tt> values (for example to * cache methods that return {@code null}). * * @since 3.1 */ public interface Cache { /** * Return the cache name. */ String getName(); /** * Return the the underlying native cache provider. */ Object getNativeCache(); /** * Return the value to which this cache maps the specified key. Returns * <code>null</code> if the cache contains no mapping for this key. * @param key key whose associated value is to be returned. * @return the value to which this cache maps the specified key, * or <code>null</code> if the cache contains no mapping for this key */ ValueWrapper get(Object key); /** * Associate the specified value with the specified key in this cache. * <p>If the cache previously contained a mapping for this key, the old * value is replaced by the specified value. * @param key the key with which the specified value is to be associated * @param value the value to be associated with the specified key */ void put(Object key, Object value); /** * Evict the mapping for this key from this cache if it is present. * @param key the key whose mapping is to be removed from the cache */ void evict(Object key); /** * Remove all mappings from the cache. */ void clear(); /** * A (wrapper) object representing a cache value. */ interface ValueWrapper { /** * Return the actual value in the cache. */ Object get(); } }
evict,put方法就是Advice的功能方法，或者可以这样去理解。
但spring并不是直接使用org.springframework.cache.Cache，spring把Cache对象交给org.springframework.cache.CacheManager来管理，下面是org.springframework.cache.CacheManager接口的定义：
/* * Copyright 2002-2011 the original author or authors. * * Licensed 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.springframework.cache; import java.util.Collection; /** * A manager for a set of {@link Cache}s. * * @since 3.1 */ public interface CacheManager { /** * Return the cache associated with the given name. * @param name cache identifier (must not be {@code null}) * @return associated cache, or {@code null} if none is found */ Cache getCache(String name); /** * Return a collection of the caches known by this cache manager. * @return names of caches known by the cache manager. */ Collection<String> getCacheNames(); }
在spring对EHCache的支持中，org.springframework.cache.ehcache.EhCacheManager就是org.springframework.cache.CacheManager的一个实现
<!-- 该Bean是一个org.springframework.cache.CacheManager对象 属性cacheManager是一个net.sf.ehcache.CacheManager对象 --> <bean id="cacheManager" class="org.springframework.cache.ehcache.EhCacheCacheManager"> <property name="cacheManager"> <bean class="org.springframework.cache.ehcache.EhCacheManagerFactoryBean"> <property name="configLocation" value="classpath:ehcache-config.xml"></property> </bean> </property> </bean>
基于xml方式的缓存配置
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:cache="http://www.springframework.org/schema/cache" xmlns:context="http://www.springframework.org/schema/context" xmlns:aop="http://www.springframework.org/schema/aop" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.1.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.1.xsd http://www.springframework.org/schema/cache http://www.springframework.org/schema/cache/spring-cache-3.1.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-3.1.xsd "> <context:component-scan base-package="com.sin90lzc"></context:component-scan> <bean id="cacheManager" class="org.springframework.cache.ehcache.EhCacheCacheManager"> <property name="cacheManager"> <bean class="org.springframework.cache.ehcache.EhCacheManagerFactoryBean"> <property name="configLocation" value="classpath:ehcache-config.xml"></property> </bean> </property> </bean> <cache:advice id="cacheAdvice" cache-manager="cacheManager"> <cache:caching> <cache:cacheable cache="dao.select" method="select" key="#id" /> <cache:cache-evict cache="dao.select" method="save" key="#obj" /> </cache:caching> </cache:advice> <aop:config> <aop:advisor advice-ref="cacheAdvice" pointcut="execution(* com.sin90lzc.train.spring_cache.simulation.DaoImpl.*(..))"/> </aop:config> </beans>
注解驱动缓存配置
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:cache="http://www.springframework.org/schema/cache" xmlns:context="http://www.springframework.org/schema/context" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.1.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.1.xsd http://www.springframework.org/schema/cache http://www.springframework.org/schema/cache/spring-cache-3.1.xsd"> <context:component-scan base-package="com.sin90lzc"></context:component-scan> <!-- 该Bean是一个org.springframework.cache.CacheManager对象 属性cacheManager是一个net.sf.ehcache.CacheManager对象 --> <bean id="cacheManager" class="org.springframework.cache.ehcache.EhCacheCacheManager"> <property name="cacheManager"> <bean class="org.springframework.cache.ehcache.EhCacheManagerFactoryBean"> <property name="configLocation" value="classpath:ehcache-config.xml"></property> </bean> </property> </bean> <cache:annotation-driven /> <!-- 启用缓存注解功能，这个是必须的，否则注解不会生效，另外，该注解一定要声明在spring主配置文件中才会生效 --> <!-- <cache:annotation-driven cache-manager="cacheManager"/> --> </beans>
package com.sin90lzc.train.spring_cache.simulation; import org.springframework.cache.annotation.CacheEvict; import org.springframework.cache.annotation.Cacheable; import org.springframework.stereotype.Component; @Component public class DaoImpl implements Dao { /** * value定义了缓存区（缓存区的名字），每个缓存区可以看作是一个Map对象 * key作为该方法结果缓存的唯一标识， */ @Cacheable(value = { "dao.select" },key="#id") @Override public Object select(int id) { System.out.println("do in function select()"); return new Object(); } @CacheEvict(value = { "dao.select" }, key="#obj") @Override public void save(Object obj) { System.out.println("do in function save(obj)"); } }
@Cacheable：负责将方法的返回值加入到缓存中
@CacheEvict：负责清除缓存
@Cacheable 支持如下几个参数：
value：缓存位置名称，不能为空，如果使用EHCache，就是ehcache.xml中声明的cache的name
key：缓存的key，默认为空，既表示使用方法的参数类型及参数值作为key，支持SpEL
condition：触发条件，只有满足条件的情况才会加入缓存，默认为空，既表示全部都加入缓存，支持SpEL
例如：
//将缓存保存进andCache，并使用参数中的userId加上一个字符串(这里使用方法名称)作为缓存的key @Cacheable(value="andCache",key="#userId + 'findById'") public SystemUser findById(String userId) { SystemUser user = (SystemUser) dao.findById(SystemUser.class, userId); return user ; } //将缓存保存进andCache，并当参数userId的长度小于32时才保存进缓存，默认使用参数值及类型作为缓存的key @Cacheable(value="andCache",condition="#userId.length < 32") public boolean isReserved(String userId) { System.out.println("hello andCache"+userId); return false; }
@CacheEvict 支持如下几个参数：
value：缓存位置名称，不能为空，同上
key：缓存的key，默认为空，同上
condition：触发条件，只有满足条件的情况才会清除缓存，默认为空，支持SpEL
allEntries：true表示清除value中的全部缓存，默认为false
例如：
//清除掉指定key的缓存 @CacheEvict(value="andCache",key="#user.userId + 'findById'") public void modifyUserRole(SystemUser user) { System.out.println("hello andCache delete"+user.getUserId()); } //清除掉全部缓存 @CacheEvict(value="andCache",allEntries=true) public final void setReservedUsers(String[] reservedUsers) { System.out.println("hello andCache deleteall"); }