二级缓存其实没啥文档，在mapper配置上
<cache eviction="LRU" flushInterval="60000" type="org.apache.ibatis.caches.memcached.XMemcachedCache" />，
然后再加个xmemcached配置文件，在项目的resources/xmemcached.xml里配置具体的地址信息, 具体配置信息如下：

	<bean class="org.mybatis.caches.xmemcached.SpringContextHolder" />
	
	<bean name="memcachedClientBuilder" class="org.mybatis.caches.xmemcached.MybatisXMemcachedClientBuilder">
		<!-- XMemcachedClientBuilder have two arguments.First is server list,and 
			second is weights array. -->
		<constructor-arg>
			<list>
				<bean class="java.net.InetSocketAddress">
					<constructor-arg>
						<value>localhost</value>
					</constructor-arg>
					<constructor-arg>
						<value>11211</value>
					</constructor-arg>
				</bean>
 				<bean class="java.net.InetSocketAddress">
					<constructor-arg>
						<value>localhost</value>
					</constructor-arg>
					<constructor-arg>
						<value>12001</value>
					</constructor-arg>
				</bean> -->
			</list>
		</constructor-arg>
 		<constructor-arg>
			<list>
				<value>1</value>
				<value>2</value>
			</list>
		</constructor-arg> -->
		<property name="connectionPoolSize" value="2"></property>
		<property name="commandFactory">
			<bean class="net.rubyeye.xmemcached.command.TextCommandFactory"></bean>
		</property>
		<property name="sessionLocator">
			<bean class="net.rubyeye.xmemcached.impl.KetamaMemcachedSessionLocator"></bean>
		</property>
		<property name="transcoder">
			<bean class="net.rubyeye.xmemcached.transcoders.SerializingTranscoder" />
		</property>
		
		<property name="keyPrefix" value="mybatis-xmemcached-"></property>
		<!-- unit:seconds -->
		<property name="expiration" value="300"></property>
	</bean>
	
	<!-- Use factory bean to build memcached client -->
	<bean name="xmemcachedClient" factory-bean="memcachedClientBuilder"
		factory-method="build" destroy-method="shutdown" />