带你深入理解MyBatis缓存机制

<mapper namespace="com.zengchuiyu.mybatis.dao.EmployeeMapper">
    <!-- 启动二级缓存功能 -->
    <cache/>

public class Employee implements Serializable {

public class CacheTest {

    private SqlSessionFactory factory;

    @Before
    public void init() throws IOException {

        factory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsStream("mybatis-config.xml"));

    }

    //测试二级缓存，（mybatis自带的）
    @Test
    public void test1(){

        SqlSession session = factory.openSession();

        EmployeeMapper mapper = session.getMapper(EmployeeMapper.class);

        Employee employee = mapper.selectEmpById(2);
        System.out.println("employee = " + employee);

        //在执行第二次查询前，关闭当前SqlSession
        session.close();

        //开启新的SqlSession
        session = factory.openSession();

        mapper = session.getMapper(EmployeeMapper.class);
        employee = mapper.selectEmpById(2);
        System.out.println("employee = " + employee);

        session.close();
    }
}

Cache Hit Ratio [com.atguigu.mybatis.EmployeeMapper]: 0.0（0/1)
Cache Hit Ratio [com.atguigu.mybatis.EmployeeMapper]: 0.5（1/2）
Cache Hit Ratio [com.atguigu.mybatis.EmployeeMapper]: 0.6666666666666666（2/3）
Cache Hit Ratio [com.atguigu.mybatis.EmployeeMapper]: 0.75（3/4）
Cache Hit Ratio [com.atguigu.mybatis.EmployeeMapper]: 0.8（4/5）

<!-- Mybatis EHCache整合包 -->
<dependency>
    <groupId>org.mybatis.caches</groupId>
    <artifactId>mybatis-ehcache</artifactId>
    <version>1.2.1</version>
</dependency>
<!-- slf4j日志门面的一个具体实现 -->
<dependency>
    <groupId>ch.qos.logback</groupId>
    <artifactId>logback-classic</artifactId>
    <version>1.2.3</version>
</dependency>

<?xml version="1.0" encoding="utf-8" ?>
<ehcache xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:noNamespaceSchemaLocation="../config/ehcache.xsd">
    <!-- 磁盘保存路径 -->
    <diskStore path="D:zengchuiyuehcache"/>
    
    <defaultCache
            maxElementsInMemory="1000"
            maxElementsOnDisk="10000000"
            eternal="false"
            overflowToDisk="true"
            timeToIdleSeconds="120"
            timeToLiveSeconds="120"
            diskExpiryThreadIntervalSeconds="120"
            memoryStoreEvictionPolicy="LRU">
    </defaultCache>
</ehcache>

<?xml version="1.0" encoding="UTF-8"?>
<configuration debug="true">
    <!-- 指定日志输出的位置 -->
    <appender name="STDOUT"
        class="ch.qos.logback.core.ConsoleAppender">
        <encoder>
            <!-- 日志输出的格式 -->
            <!-- 按照顺序分别是：时间、日志级别、线程名称、打印日志的类、日志主体内容、换行 -->
            <pattern>[%d{HH:mm:ss.SSS}] [%-5level] [%thread] [%logger] [%msg]%n</pattern>
        </encoder>
    </appender>
    
    <!-- 设置全局日志级别。日志级别按顺序分别是：DEBUG、INFO、WARN、ERROR -->
    <!-- 指定任何一个日志级别都只打印当前级别和后面级别的日志。 -->
    <root level="DEBUG">
        <!-- 指定打印日志的appender，这里通过“STDOUT”引用了前面配置的appender -->
        <appender-ref ref="STDOUT" />
    </root>
    
    <!-- 根据特殊需求指定局部日志级别 -->
    <logger name="com.atguigu.crowd.mapper" level="DEBUG"/>
    
</configuration>