Mybatis 二级缓存

之前我们介绍过映射器与XML配置职责分离，本篇我们在此基础上介绍Mybatis中二级缓存的使用。

如果您对映射器与XML配置职责分离不太了解，建议您先进行了解后再阅读本篇，可以参考：

Mybatis 映射器与XML配置职责分离https://blog.csdn.net/m1729339749/article/details/133196679

一、数据准备

这里我们直接使用脚本初始化数据库中的数据

-- 如果数据库不存在则创建数据库
CREATE DATABASE IF NOT EXISTS demo DEFAULT CHARSET utf8;
-- 切换数据库
USE demo;
-- 创建用户表
CREATE TABLE IF NOT EXISTS T_USER(
  ID INT PRIMARY KEY,
  USERNAME VARCHAR(32) NOT NULL,
  AGE INT NOT NULL 
);
-- 插入用户数据
INSERT INTO T_USER(ID, USERNAME, AGE)
VALUES(1, '张三', 20),(2, '李四', 22),(3, '王五', 24);

创建了一个名称为demo的数据库；并在库里创建了名称为T_USER的用户表并向表中插入了数据

二、创建实体类

在cn.horse.demo下创建UserInfo、UserInfoQuery类，另外需要特别注意缓存的对象类型必须实现Serializable接口

UserInfo类：

package cn.horse.demo;

import java.io.Serializable;

public class UserInfo implements Serializable {
    private static final long serialVersionUID = 9213975268411777481L;
    private Integer id;
    private String name;
    private Integer age;

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

    public Integer getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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

    public Integer getAge() {
        return age;
    }

    @Override
    public String toString() {
        StringBuilder stringBuilder = new StringBuilder();
        stringBuilder.append('{');
        stringBuilder.append("id: " + this.id);
        stringBuilder.append(", ");
        stringBuilder.append("name: " + this.name);
        stringBuilder.append(", ");
        stringBuilder.append("age: " + this.age);
        stringBuilder.append('}');
        return stringBuilder.toString();
    }
}

UserInfoQuery类：

package cn.horse.demo;

public class UserInfoQuery {

    private Integer startAge;
    private Integer endAge;

    public void setStartAge(Integer startAge) {
        this.startAge = startAge;
    }

    public Integer getStartAge() {
        return startAge;
    }

    public void setEndAge(Integer endAge) {
        this.endAge = endAge;
    }

    public Integer getEndAge() {
        return endAge;
    }
}

三、创建映射器、Mapper配置

在cn.horse.demo下创建UserInfoMapper接口

UserInfoMapper接口：

package cn.horse.demo;

import org.apache.ibatis.annotations.*;

import java.util.List;

public interface UserInfoMapper {

    List<UserInfo> find(@Param("query") UserInfoQuery query);

    Integer insert(@Param("userInfoList") List<UserInfo> userInfoList);

    Integer update(@Param("userInfoList") List<UserInfo> userInfoList);

    Integer delete(@Param("idList") List<Integer> idList);
}

在resources下创建cn/horse/demo目录，并在此目录下创建UserInfoMapper.xml配置文件

UserInfoMapper.xml配置：

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="cn.horse.demo.UserInfoMapper">

    <cache />

    <resultMap id="userInfoMap" type="cn.horse.demo.UserInfo">
        <result column="ID" property="id" />
        <result column="USERNAME" property="name"/>
        <result column="AGE" property="age"/>
    </resultMap>

    <select id="find" parameterType="cn.horse.demo.UserInfoQuery" resultMap="userInfoMap">
        SELECT
            ID,
            USERNAME,
            AGE
        FROM T_USER
        <where>
            <if test="null != query.startAge">
                AND AGE &gt;= #{query.startAge}
            </if>
            <if test="null != query.endAge">
                AND AGE &lt;= #{query.endAge}
            </if>
        </where>
    </select>

    <insert id="insert">
        INSERT INTO T_USER(ID,
            USERNAME,
            AGE)
        VALUES
        <foreach collection="userInfoList" item="userInfo" separator=",">
            (#{userInfo.id}, #{userInfo.name}, #{userInfo.age})
        </foreach>
    </insert>

    <update id="update">
        <foreach collection="userInfoList" item="userInfo" separator=";" close=";">
            UPDATE T_USER
            <set>
                <if test="null != userInfo.name and '' != userInfo.name">
                    USERNAME = #{userInfo.name},
                </if>
                <if test="null != userInfo.age">
                    AGE = #{userInfo.age},
                </if>
            </set>
            WHERE ID = #{userInfo.id}
        </foreach>
    </update>

    <delete id="delete">
        DELETE FROM T_USER
        <where>
            ID IN
            <foreach collection="idList" item="id" open="(" separator="," close=")">
                #{id}
            </foreach>
        </where>
    </delete>
</mapper>

注意：cache标签代表在此命名空间下使用二级缓存

四、引入配置文件

在resources下新建mybatis-config.xml配置文件，并引入UserInfoMapper映射器。

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <settings>
        <setting name="logImpl" value="JDK_LOGGING"/>
    </settings>

    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="org.gjt.mm.mysql.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/demo?useUnicode=true&amp;useSSL=false&amp;characterEncoding=utf8&amp;allowMultiQueries=true"/>
                <property name="username" value="root"/>
                <property name="password" value="horse"/>
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <mapper class="cn.horse.demo.UserInfoMapper" />
    </mappers>
</configuration>

这里我们使用mapper引入映射器，只需要设置class属性为UserInfoMapper接口的全限类名。

五、启动程序配置

1、会话工具类

在cn.horse.demo包下新建SqlSessionUtils工具类

package cn.horse.demo;

import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import java.io.InputStream;
import java.util.Objects;

public class SqlSessionUtils {

    private static final SqlSessionFactory sqlSessionFactory;
    static {
        // 读取mybatis配置文件
        InputStream inputStream = ClassLoader.getSystemClassLoader().getResourceAsStream("mybatis-config.xml");
        // 根据配置创建SqlSession工厂
        sqlSessionFactory = new SqlSessionFactoryBuilder()
                .build(inputStream);
    }

    /**
     * 开启会话
     * @return
     */
    public static SqlSession openSession() {
        return sqlSessionFactory.openSession();
    }

    /**
     * 关闭会话
     * @param sqlSession
     */
    public static void closeSession(SqlSession sqlSession) {
        if(Objects.nonNull(sqlSession)) {
            sqlSession.close();
        }
    }
}

2、JDK 日志系统配置

在resources的目录下新建logging.properties配置文件

handlers=java.util.logging.ConsoleHandler
.level=INFO

cn.horse.demo.UserInfoMapper.level=FINER
java.util.logging.ConsoleHandler.level=ALL
java.util.logging.ConsoleHandler.formatter=java.util.logging.SimpleFormatter
java.util.logging.SimpleFormatter.format=%1$tY-%1$tm-%1$td %1$tT.%1$tL %4$s %3$s - %5$s%6$s%n

在cn.horse.demo下创建JdkLogConfig类

JdkLogConfig类：

package cn.horse.demo;

import java.io.IOException;
import java.io.InputStream;
import java.util.logging.LogManager;

public class JdkLogConfig {

    public JdkLogConfig() {
        try {
            InputStream inputStream = ClassLoader.getSystemClassLoader().getResourceAsStream("logging.properties");
            LogManager.getLogManager().readConfiguration(inputStream);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
}

3、启动程序配置

package cn.horse.demo;

import org.apache.ibatis.session.SqlSession;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.function.Consumer;
import java.util.logging.Level;
import java.util.logging.Logger;

public class Main {

    private static final Logger LOGGER;

    static {
        // 引入JDK日志配置
        System.setProperty("java.util.logging.config.class", "cn.horse.demo.JdkLogConfig");
        LOGGER = Logger.getLogger("cn.horse.demo.Main");
    }

    public static void main(String[] args) throws InterruptedException {
    }

    private static void batchInsert(final List<UserInfo> userInfoList) {
        LOGGER.log(Level.FINER, "--------------- 插入 ----------------");
        execute((UserInfoMapper userInfoMapper) -> {
            Integer total = userInfoMapper.insert(userInfoList);
            LOGGER.log(Level.INFO, "插入条数: " + total);
        });
    }

    private static void batchUpdate(final List<UserInfo> userInfoList) {
        LOGGER.log(Level.FINER, "--------------- 更新 ----------------");
        execute((UserInfoMapper userInfoMapper) -> {
            Integer total = userInfoMapper.update(userInfoList);
            LOGGER.log(Level.INFO, "更新条数: " + total);
        });
    }

    private static void batchDelete(final List<Integer> idList) {
        LOGGER.log(Level.FINER, "--------------- 删除 ----------------");
        execute((UserInfoMapper userInfoMapper) -> {
            Integer total = userInfoMapper.delete(idList);
            LOGGER.log(Level.INFO, "删除条数: " + total);
        });
    }

    private static void selectGreaterThan(Integer age) {
        LOGGER.log(Level.FINER, "--------------- 查询 ----------------");
        execute((UserInfoMapper userInfoMapper) -> {
            UserInfoQuery query = new UserInfoQuery();
            query.setStartAge(age);
            List<UserInfo> userInfoList = userInfoMapper.find(query);
            for (UserInfo userInfo: userInfoList) {
                LOGGER.log(Level.INFO, userInfo.toString());
            }
        });
    }

    private static void execute(Consumer<UserInfoMapper> function) {
        SqlSession sqlSession = null;
        try {
            sqlSession = SqlSessionUtils.openSession();
            function.accept(sqlSession.getMapper(UserInfoMapper.class));
            sqlSession.commit();
        } finally {
            SqlSessionUtils.closeSession(sqlSession);
        }
    }
}

execute方法用于执行操作，方法中使用sqlSession.getMapper方法获取映射器对象，然后将映射器对象具体的执行操作委托给了Consumer对象。

六、何时存取二级缓存

// 查询
selectGreaterThan(20);
// 查询
selectGreaterThan(20);

执行后的结果如下：

从打印的SQL执行记录可以看出，第二次查询时使用到了缓存，说明在第一次查询时就写入了缓存，其实是select标签中的SQL语句执行时会使用缓存或者对查询结果进行缓存。

七、何时过期二级缓存

1、insert标签

// 查询
selectGreaterThan(20);
// 插入
List<UserInfo> insertUserInfoList = new ArrayList<>();
UserInfo insertUserInfo1 = new UserInfo();
insertUserInfo1.setId(5);
insertUserInfo1.setName("王五1");
insertUserInfo1.setAge(5);
insertUserInfoList.add(insertUserInfo1);
UserInfo insertUserInfo2 = new UserInfo();
insertUserInfo2.setId(6);
insertUserInfo2.setName("王五2");
insertUserInfo2.setAge(6);
insertUserInfoList.add(insertUserInfo2);
batchInsert(insertUserInfoList);
// 查询
selectGreaterThan(20);

执行后的结果如下：

从打印的SQL执行记录可以看出，第二次查询时未使用缓存，说明在第一次查询时写入的缓存过期了，其实是insert标签中的SQL语句执行后会使缓存过期。

2、update标签

// 查询
selectGreaterThan(20);
// 更新
List<UserInfo> updateUserInfoList = new ArrayList<>();
UserInfo updateUserInfo1 = new UserInfo();
updateUserInfo1.setId(5);
updateUserInfo1.setName("王五11");
updateUserInfoList.add(updateUserInfo1);
UserInfo updateUserInfo2 = new UserInfo();
updateUserInfo2.setId(6);
updateUserInfo2.setAge(26);
updateUserInfoList.add(updateUserInfo2);
batchUpdate(updateUserInfoList);
// 查询
selectGreaterThan(20);

执行后的结果如下：

从打印的SQL执行记录可以看出，第二次查询时未使用缓存，说明在第一次查询时写入的缓存过期了，其实是update标签中的SQL语句执行后会使缓存过期。

3、delete标签

// 查询
selectGreaterThan(20);
// 删除
batchDelete(Arrays.asList(5, 6));
// 查询
selectGreaterThan(20);

执行后的结果如下：

从打印的SQL执行记录可以看出，第二次查询时未使用缓存，说明在第一次查询时写入的缓存过期了，其实是delete标签中的SQL语句执行后会使缓存过期。

八、可能出现的问题

2023-09-19 17:27:58.570 较详细 cn.horse.demo.Main - --------------- 查询 ----------------
2023-09-19 17:27:58.850 详细 cn.horse.demo.UserInfoMapper - Cache Hit Ratio [cn.horse.demo.UserInfoMapper]: 0.0
2023-09-19 17:27:59.009 详细 cn.horse.demo.UserInfoMapper.find - ==>  Preparing: SELECT ID, USERNAME, AGE FROM T_USER WHERE AGE >= ? 
2023-09-19 17:27:59.032 详细 cn.horse.demo.UserInfoMapper.find - ==> Parameters: 20(Integer)
2023-09-19 17:27:59.039 较详细 cn.horse.demo.UserInfoMapper.find - <==    Columns: ID, USERNAME, AGE
2023-09-19 17:27:59.039 较详细 cn.horse.demo.UserInfoMapper.find - <==        Row: 1, 张三, 20
2023-09-19 17:27:59.040 较详细 cn.horse.demo.UserInfoMapper.find - <==        Row: 2, 李四, 22
2023-09-19 17:27:59.041 较详细 cn.horse.demo.UserInfoMapper.find - <==        Row: 3, 王五, 24
2023-09-19 17:27:59.041 详细 cn.horse.demo.UserInfoMapper.find - <==      Total: 3
2023-09-19 17:27:59.042 信息 cn.horse.demo.Main - {id: 1, name: 张三, age: 20}
2023-09-19 17:27:59.043 信息 cn.horse.demo.Main - {id: 2, name: 李四, age: 22}
2023-09-19 17:27:59.043 信息 cn.horse.demo.Main - {id: 3, name: 王五, age: 24}
Exception in thread "main" org.apache.ibatis.cache.CacheException: Error serializing object.  Cause: java.io.NotSerializableException: cn.horse.demo.UserInfo
	at org.apache.ibatis.cache.decorators.SerializedCache.serialize(SerializedCache.java:102)
	at org.apache.ibatis.cache.decorators.SerializedCache.putObject(SerializedCache.java:56)
	at org.apache.ibatis.cache.decorators.LoggingCache.putObject(LoggingCache.java:51)
	at org.apache.ibatis.cache.decorators.SynchronizedCache.putObject(SynchronizedCache.java:45)
	at org.apache.ibatis.cache.decorators.TransactionalCache.flushPendingEntries(TransactionalCache.java:122)
	at org.apache.ibatis.cache.decorators.TransactionalCache.commit(TransactionalCache.java:105)
	at org.apache.ibatis.cache.TransactionalCacheManager.commit(TransactionalCacheManager.java:44)
	at org.apache.ibatis.executor.CachingExecutor.close(CachingExecutor.java:61)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.close(DefaultSqlSession.java:264)
	at cn.horse.demo.SqlSessionUtils.closeSession(SqlSessionUtils.java:35)
	at cn.horse.demo.Main.execute(Main.java:120)
	at cn.horse.demo.Main.selectLessThan(Main.java:103)
	at cn.horse.demo.Main.main(Main.java:25)
Caused by: java.io.NotSerializableException: cn.horse.demo.UserInfo
	at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1184)
	at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:348)
	at java.util.ArrayList.writeObject(ArrayList.java:768)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:1154)
	at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1496)
	at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
	at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
	at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:348)
at org.apache.ibatis.cache.decorators.SerializedCache.serialize(SerializedCache.java:97)

从日志中可以看出，出现问题的原因是缓存的对象类型未实现Serializable接口；只需要将缓存的对象类型实现Serializable接口即可解决。