二级缓存是多个SqlSession共享的，其作用域是mapper的同一个namespace，不同的sqlSession两次执行相同namespace下的sql语句且向sql中传递参数也相同即最终执行相同的sql语句，第一次执行完毕会将数据库中查询的数据写到缓存（内存），第二次会从缓存中获取数据将不再从数据库查询，从而提高查询效率。Mybatis默认没有开启二级缓存需要在setting全局参数中配置开启二级缓存。

下面是使用Ehcache来作为Mybatis二级缓存的实例：

application.properties开启mybatis中二级缓存

==mybatis.configuration.cache-enabled=true==

默认二级缓存是开启的

server.port=80
# 数据源配置
spring.datasource.url=jdbc:mysql://localhost:3306/ssb_test
spring.datasource.driver-class-name=com.mysql.jdbc.Driver
spring.datasource.username=root
spring.datasource.password=root
#连接池配置
#spring.datasource.type=org.apache.commons.dbcp2.BasicDataSource

#mybatis
#entity扫描的包名
mybatis.type-aliases-package=com.xiaolyuh.domain.model
#Mapper.xml所在的位置
mybatis.mapper-locations=classpath*:/mybaits/*Mapper.xml
#开启MyBatis的二级缓存
mybatis.configuration.cache-enabled=true

#pagehelper
pagehelper.helperDialect=mysql
pagehelper.reasonable=true
pagehelper.supportMethodsArguments=true
pagehelper.params=count=countSql

#日志配置
logging.level.com.xiaolyuh=debug
logging.level.org.springframework.web=debug
logging.level.org.springframework.transaction=debug
logging.level.org.mybatis=debug

debug=false

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <artifactId>spring-boot-student-mybatis-ehcache</artifactId>
    <packaging>jar</packaging>

    <name>spring-boot-student-mybatis-ehcache</name>
    <description>Demo Mybatis ehcache for Spring Boot</description>

    <parent>
        <groupId>com.xiaolyuh</groupId>
        <artifactId>spring-boot-student</artifactId>
        <version>0.0.1-SNAPSHOT</version>
        <relativePath />
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
        </dependency>

        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>1.3.0</version>
        </dependency>
        <!--pagehelper -->
        <dependency>
            <groupId>com.github.pagehelper</groupId>
            <artifactId>pagehelper-spring-boot-starter</artifactId>
            <version>1.1.1</version>
        </dependency>

        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>1.2.31</version>
        </dependency>

        <dependency>
            <groupId>net.sf.ehcache</groupId>
            <artifactId>ehcache</artifactId>
        </dependency>

        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis-ehcache</artifactId>
            <version>1.0.0</version>
        </dependency>
    </dependencies>

</project>

Ehcache配置

在src\main\resources目录下创建ehcache.xml文件，内容如下：

<?xml version="1.0" encoding="UTF-8"?>
<ehcache>

    <!--
        http://www.cnblogs.com/lzy1991/p/5335249.html
        http://www.cnblogs.com/little-fly/p/6251439.html
        缓存配置
           diskStore：指定数据在磁盘中的存储位置。
           name:缓存名称。
           defaultCache：当借助CacheManager.add("demoCache")创建Cache时，EhCache便会采用<defalutCache/>指定的的管理策略,以下属性是必须的：
           maxElementsInMemory：缓存最大个数。
           eternal:对象是否永久有效，一但设置了，timeout将不起作用。
           timeToIdleSeconds：设置对象在失效前的允许闲置时间（单位：秒）。仅当eternal=false对象不是永久有效时使用，可选属性，默认值是0，也就是可闲置时间无穷大。
           timeToLiveSeconds：设置对象在失效前允许存活时间（单位：秒）。最大时间介于创建时间和失效时间之间。仅当eternal=false对象不是永久有效时使用，默认是0.，也就是对象存活时间无穷大。
           overflowToDisk：当内存中对象数量达到maxElementsInMemory时，Ehcache将会对象写到磁盘中。
           diskSpoolBufferSizeMB：这个参数设置DiskStore（磁盘缓存）的缓存区大小。默认是30MB。每个Cache都应该有自己的一个缓冲区。
           maxElementsOnDisk：硬盘最大缓存个数。
           diskPersistent：是否缓存虚拟机重启期数据 Whether the disk store persists between restarts of the Virtual Machine. The default value is false.
           diskExpiryThreadIntervalSeconds：磁盘失效线程运行时间间隔，默认是120秒。
           memoryStoreEvictionPolicy：当达到maxElementsInMemory限制时，Ehcache将会根据指定的策略去清理内存。默认策略是LRU（最近最少使用）。你可以设置为FIFO（先进先出）或是LFU（较少使用）。
           clearOnFlush：内存数量最大时是否清除。
    -->
    <diskStore path="e:\ehcache" />
    <defaultCache
            maxElementsInMemory="10000"
            eternal="false"
            timeToIdleSeconds="120"
            timeToLiveSeconds="120"
            overflowToDisk="true"
            maxElementsOnDisk="10000000"
            diskPersistent="false"
            diskExpiryThreadIntervalSeconds="120"
            memoryStoreEvictionPolicy="LRU"
    />
</ehcache>

Mapper文件

<cache /> 添加这个节点会默认将该namespace下所有的的select语句缓存。如果不需要进行缓存，需要设置useCache="false"。

 <select id="findByPage" resultMap="BaseResultMap" useCache="false">

完整的Mapper文件，如下：

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
<mapper namespace="com.xiaolyuh.domain.mapper.PersonMapper">
    <!--mybatis ehcache缓存配置 -->
    <!-- 以下两个<cache>标签二选一,第一个可以输出日志,第二个不输出日志 -->
    <!--<cache type="org.mybatis.caches.ehcache.LoggingEhcache" />
    <cache type="org.mybatis.caches.ehcache.EhcacheCache"/>-->

    <!--根据需求调整缓存参数：-->
    <cache type="org.mybatis.caches.ehcache.EhcacheCache">
        <property name="timeToIdleSeconds" value="3600"/>
        <property name="timeToLiveSeconds" value="3600"/>
        <!-- 同ehcache参数maxElementsInMemory -->
        <property name="maxEntriesLocalHeap" value="1000"/>
        <!-- 同ehcache参数maxElementsOnDisk -->
        <property name="maxEntriesLocalDisk" value="10000000"/>
        <property name="memoryStoreEvictionPolicy" value="LRU"/>
    </cache>

    <resultMap id="BaseResultMap" type="com.xiaolyuh.domain.model.Person">
        <!--
          WARNING - @mbggenerated
          This element is automatically generated by MyBatis Generator, do not modify.
        -->
        <id column="id" property="id" jdbcType="BIGINT"/>
        <result column="name" property="name" jdbcType="VARCHAR"/>
        <result column="age" property="age" jdbcType="INTEGER"/>
        <result column="address" property="address" jdbcType="VARCHAR"/>
    </resultMap>
    <sql id="Base_Column_List">
        <!--
          WARNING - @mbggenerated
          This element is automatically generated by MyBatis Generator, do not modify.
        -->
        id, name, age, address
    </sql>
    <select id="selectByPrimaryKey" resultMap="BaseResultMap" parameterType="java.lang.Long">
        <!--
          WARNING - @mbggenerated
          This element is automatically generated by MyBatis Generator, do not modify.
        -->
        select
        <include refid="Base_Column_List"/>
        from person
        where id = #{id,jdbcType=BIGINT}
    </select>
    <delete id="deleteByPrimaryKey" parameterType="java.lang.Long">
        <!--
          WARNING - @mbggenerated
          This element is automatically generated by MyBatis Generator, do not modify.
        -->
        delete from person
        where id = #{id,jdbcType=BIGINT}
    </delete>
    <insert id="insert" parameterType="com.xiaolyuh.domain.model.Person">
        <!--
          WARNING - @mbggenerated
          This element is automatically generated by MyBatis Generator, do not modify.
        -->
        <selectKey resultType="java.lang.Long" keyProperty="id" order="AFTER">
            SELECT LAST_INSERT_ID()
        </selectKey>
        insert into person (name, age, address
        )
        values (#{name,jdbcType=VARCHAR}, #{age,jdbcType=INTEGER}, #{address,jdbcType=VARCHAR}
        )
    </insert>
    <insert id="insertSelective" parameterType="com.xiaolyuh.domain.model.Person">
        <!--
          WARNING - @mbggenerated
          This element is automatically generated by MyBatis Generator, do not modify.
        -->
        <selectKey resultType="java.lang.Long" keyProperty="id" order="AFTER">
            SELECT LAST_INSERT_ID()
        </selectKey>
        insert into person
        <trim prefix="(" suffix=")" suffixOverrides=",">
            <if test="name != null">
                name,
            </if>
            <if test="age != null">
                age,
            </if>
            <if test="address != null">
                address,
            </if>
        </trim>
        <trim prefix="values (" suffix=")" suffixOverrides=",">
            <if test="name != null">
                #{name,jdbcType=VARCHAR},
            </if>
            <if test="age != null">
                #{age,jdbcType=INTEGER},
            </if>
            <if test="address != null">
                #{address,jdbcType=VARCHAR},
            </if>
        </trim>
    </insert>
    <update id="updateByPrimaryKeySelective" parameterType="com.xiaolyuh.domain.model.Person">
        <!--
          WARNING - @mbggenerated
          This element is automatically generated by MyBatis Generator, do not modify.
        -->
        update person
        <set>
            <if test="name != null">
                name = #{name,jdbcType=VARCHAR},
            </if>
            <if test="age != null">
                age = #{age,jdbcType=INTEGER},
            </if>
            <if test="address != null">
                address = #{address,jdbcType=VARCHAR},
            </if>
        </set>
        where id = #{id,jdbcType=BIGINT}
    </update>
    <update id="updateByPrimaryKey" parameterType="com.xiaolyuh.domain.model.Person">
        <!--
          WARNING - @mbggenerated
          This element is automatically generated by MyBatis Generator, do not modify.
        -->
        update person
        set name = #{name,jdbcType=VARCHAR},
        age = #{age,jdbcType=INTEGER},
        address = #{address,jdbcType=VARCHAR}
        where id = #{id,jdbcType=BIGINT}
    </update>

    <!-- 对这个语句useCache="true"默认是true，可以不写 -->
    <select id="findAll" resultMap="BaseResultMap" useCache="true">
        select
        <include refid="Base_Column_List"/>
        from person
    </select>

    <!-- 对这个语句禁用二级缓存 -->
    <select id="findByPage" resultMap="BaseResultMap" useCache="false">
        select
        <include refid="Base_Column_List"/>
        from person
    </select>
</mapper>

实体类

package com.xiaolyuh.domain.model;

import java.io.Serializable;

public class Person implements Serializable {

    private Long id;

    /**
     * 名称
     */
    private String name;

    /**
     * 年龄
     */
    private Integer age;

    /**
     * 地址
     */
    private String address;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }
}

Mapper-类

package com.xiaolyuh.domain.mapper;

import com.github.pagehelper.Page;
import com.xiaolyuh.domain.model.Person;
import org.apache.ibatis.annotations.Mapper;

import java.util.List;

@Mapper//声明成mybatis Dao层的Bean，也可以在配置类上使用@MapperScan("com.xiaolyuh.domain.mapper")注解声明
public interface PersonMapper {

    int deleteByPrimaryKey(Long id);

    int insert(Person record);

    int insertSelective(Person record);

    Person selectByPrimaryKey(Long id);

    int updateByPrimaryKeySelective(Person record);

    int updateByPrimaryKey(Person record);

    /**
     * 获取所有数据
     * @return
     */
    List<Person> findAll();

    /**
     * 分页查询数据
     * @return
     */
    Page<Person> findByPage();
}

Severice接口类

package com.xiaolyuh.service;

import com.github.pagehelper.Page;
import com.xiaolyuh.domain.model.Person;

import java.util.List;

/**
 * Created by yuhao.wang on 2017/6/19.
 */
public interface PersonService {

    List<Person> findAll();

    /**
     * 分页查询
     * @param pageNo 页号
     * @param pageSize 每页显示记录数
     * @return
     */
    Page<Person> findByPage(int pageNo, int pageSize);

    void insert(Person person);
}

Severice实现类

package com.xiaolyuh.service.impl;

import com.github.pagehelper.Page;
import com.github.pagehelper.PageHelper;
import com.xiaolyuh.domain.mapper.PersonMapper;
import com.xiaolyuh.domain.model.Person;
import com.xiaolyuh.service.PersonService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

import java.util.List;

/**
 * Created by yuhao.wang on 2017/6/19.
 */
@Service
@Transactional(readOnly = true)
public class PersonServiceImpl implements PersonService {

    @Autowired
    private PersonMapper personMapper;

    @Override
    public List<Person> findAll() {
        return personMapper.findAll();
    }

    @Override
    public Page<Person> findByPage(int pageNo, int pageSize) {
        PageHelper.startPage(pageNo, pageSize);
        return personMapper.findByPage();
    }

    @Override
    @Transactional
    public void insert(Person person) {
        personMapper.insert(person);
    }

}

测试类

package com.xiaolyuh;

import com.github.pagehelper.Page;
import com.xiaolyuh.domain.model.Person;
import com.xiaolyuh.service.PersonService;
import org.junit.Assert;
import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import com.alibaba.fastjson.JSON;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

import java.util.List;

@RunWith(SpringRunner.class)
@SpringBootTest
public class PersonMapperTests {

    private Logger logger = LoggerFactory.getLogger(PersonMapperTests.class);

    @Autowired
    private PersonService personService;

    @Before
    public void testInsert() {
        Person person = new Person();
        person.setName("测试");
        person.setAddress("address");
        person.setAge(10);
        personService.insert(person);

        Assert.assertNotNull(person.getId());
        logger.debug(JSON.toJSONString(person));
    }

    @Test
    public void testFindAll() {
        List<Person> persons = personService.findAll();

        Assert.assertNotNull(persons);
        logger.debug(JSON.toJSONString(persons));
    }

    @Test
    public void testFindByPage() {
        Page<Person> persons = personService.findByPage(1, 2);

        Assert.assertNotNull(persons);
        logger.debug(persons.toString());
        logger.debug(JSON.toJSONString(persons));
    }

    @Test
    public void testCacheByPage() {
        long begin = System.currentTimeMillis();
        List<Person> persons = personService.findAll();
        long ing = System.currentTimeMillis();
        personService.findAll();
        long end = System.currentTimeMillis();
        logger.debug("第一次请求时间：" + (ing - begin) + "ms");
        logger.debug("第二次请求时间:" + (end - ing) + "ms");

        Assert.assertNotNull(persons);
        logger.debug(persons.toString());
        logger.debug(JSON.toJSONString(persons));
    }

}

执行测试类，打印日志信息

 Cache Hit Ratio [com.xiaolyuh.domain.mapper.PersonMapper]: 0.5
2017-06-28 10:15:32.214 DEBUG 10472 --- [           main] org.mybatis.spring.SqlSessionUtils       : Releasing transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@3f6c2763]
2017-06-28 10:15:32.214 DEBUG 10472 --- [           main] org.mybatis.spring.SqlSessionUtils       : Transaction synchronization committing SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@3f6c2763]
2017-06-28 10:15:32.214 DEBUG 10472 --- [           main] org.mybatis.spring.SqlSessionUtils       : Transaction synchronization deregistering SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@3f6c2763]
2017-06-28 10:15:32.214 DEBUG 10472 --- [           main] org.mybatis.spring.SqlSessionUtils       : Transaction synchronization closing SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@3f6c2763]
2017-06-28 10:15:32.223 DEBUG 10472 --- [           main] com.xiaolyuh.PersonMapperTests           : 第一次请求时间：26ms
2017-06-28 10:15:32.223 DEBUG 10472 --- [           main] com.xiaolyuh.PersonMapperTests           : 第二次请求时间:11ms

源码

https://github.com/wyh-spring-ecosystem-student/spring-boot-student/tree/releases

spring-boot-student-mybatis-ehcache工程