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");
}