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11.4 注解使用二级缓存

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11.4 注解使用二级缓存

项目结构

数据库表

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# 创建数据库表
DROP TABLE IF EXISTS `tb_user`;
CREATE TABLE `tb_user` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(18) DEFAULT NULL,
  `sex` char(2) DEFAULT NULL,
  `age` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
# 插入数据
INSERT INTO `tb_user` VALUES ('1', '小明', '男', '21');
INSERT INTO `tb_user` VALUES ('2', '小王', '男', '22');
INSERT INTO `tb_user` VALUES ('3', '小丽', '女', '18');
INSERT INTO `tb_user` VALUES ('4', '小芳', '女', '18');
INSERT INTO `tb_user` VALUES ('5', '小王', '男', '22');

mybatis相关配置

db.properties

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# 保存为db.properties文件,然后在mybatis-config.xml中通过下面标签引入:
# <properties resource="db.properties"/>
# 下面的标签放在mybatis-config.xml文件的environments标签的environment子标签的子标签dataSource标签中
# <property name="driver" value="${driver}"/><property name="url" value="${url}"/><property name="username" value="${username}"/><property name="password" value="${password}"/>
driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/mybatis
username=root
password=root

log4j.xml

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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE log4j:configuration 
    PUBLIC "-//LOG4J//DTD LOG4J//EN" 
    "https://logging.apache.org/log4j/1.2/apidocs/org/apache/log4j/xml/doc-files/log4j.dtd" >
<!-- 请在mybatis-config.xml中配置如下设置 -->
<!-- <settings> -->
<!--     <setting -->
<!--         name="logImpl" -->
<!--         value="log4j"/> -->
<!-- </settings> -->
<log4j:configuration>
    <appender
        name="STDOUT"
        class="org.apache.log4j.ConsoleAppender">
        <layout class="org.apache.log4j.PatternLayout">
            <param
                name="ConversionPattern"
                value="%5p [%t] %m%n"/>
        </layout>
    </appender>
    <logger name="mapper.UserMapper">
        <level value="DEBUG"/>
    </logger>
    <root>
        <level value="ERROR"/>
        <appender-ref ref="STDOUT"/>
    </root>
</log4j:configuration>

mybatis-config.xml

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<?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">
<!-- 该配置文件包含对 MyBatis 系统的核心设置 -->
<configuration>
    <properties resource="db.properties"/>
    <settings>
        <setting
            name="logImpl"
            value="log4j"/>
    </settings>
    <environments default="mysql">
        <environment id="mysql">
            <transactionManager type="JDBC"/>
            <dataSource type="pooled">
                <property
                    name="driver"
                    value="${driver}"/>
                <property
                    name="url"
                    value="${url}"/>
                <property
                    name="username"
                    value="${username}"/>
                <property
                    name="password"
                    value="${password}"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper class="mapper.UserMapper"/>
    </mappers>
</configuration>

持久化对象

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package domain;
import java.io.Serializable;
public class User
    implements Serializable
{
    // 使用缓存需要可序列话
    private static final long serialVersionUID = 2667279148834038605L;
    private Integer id;
    private String name;
    private String sex;
    private Integer age;
    public User()
    {}
    // 此处省略getter和setter方法,请自己补上
    @Override
    public String toString()
    {
        return "User [id=" + id + ", name=" + name + ", sex=" + sex + ", age=" + age + "]";
    }
}

mapper接口

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package mapper;
import java.util.List;
import org.apache.ibatis.annotations.CacheNamespace;
import org.apache.ibatis.annotations.Delete;
import org.apache.ibatis.annotations.Options;
import org.apache.ibatis.annotations.Select;
import org.apache.ibatis.cache.decorators.LruCache;
import domain.User;
@CacheNamespace(
    eviction = LruCache.class,
    flushInterval = 60000,
    size = 512,
    readWrite = true
)
public interface UserMapper{
    /**
     * 根据id查询用户信息.
     * 
     * @param  id
     * @return
     */
    @Select("select * from tb_user where id=#{id}")
    @Options(useCache = true)
    User selectUserById(Integer id);
    /**
     * 查询所有的用户信息.
     * 
     * @return
     */
    @Select("select * from tb_user")
    @Options(useCache = true)
    List<User> selectAllUsers();
    /**
     * 根据id删除用户信息.
     * 
     * @param id
     */
    @Delete("delete from tb_user where id=#{id}")
    void deleteUserById(Integer id);
}

UserMapper接口中只是将之前写在XML文件当中的二级缓存配置写在了注解当中,其他并无不同。
@CacheNamespace注解用来配置二级缓存,如下所示:

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@CacheNamespace(
    eviction = LruCache.class,
    flushInterval = 60000,
    size = 512,
    readWrite = true
)
  • eviction属性表示要使用的回收策略的class,所有回收策略的类型都位于org.apache.ibatis.cache.decorators包下。
  • flushInterval表示刷新时间间隔,单位为毫秒
  • size表示缓存数目
  • readWrite=true表示只读

SqlSession工厂类

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package fractory;
import java.io.IOException;
import java.io.InputStream;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
public class SqlSessionFratoryTools {
    private static SqlSessionFactory sqlSessionFactory = null;
    static
    {
        try
        {
            InputStream mybatisConfigXML = Resources.getResourceAsStream("mybatis-config.xml");
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(mybatisConfigXML);
        } catch (IOException e)
        {
            e.printStackTrace();
        }
    }
    public static SqlSession getSqlSession()
    {
        return sqlSessionFactory.openSession();
    }
}

测试类

按id查询

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package test;
import org.apache.ibatis.session.SqlSession;
import domain.User;
import fractory.SqlSessionFratoryTools;
import mapper.UserMapper;
public class SelectTest{
    public static void main(String[] args)
    {
        SqlSession sqlSession = null;
        try
        {
            // 加载mybatis-config.xml,获取SqlSession实例
            sqlSession = SqlSessionFratoryTools.getSqlSession();
            // 获取mapper接口代理对象
            UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
            User user = userMapper.selectUserById(1);
            System.out.println(user);
            // 关闭一级缓存
            sqlSession.close();
            // 重新获取会话
            sqlSession = SqlSessionFratoryTools.getSqlSession();
            // 重新获取mapper接口代理对象
            userMapper = sqlSession.getMapper(UserMapper.class);
            System.out.println("-----------------------------------------------");
            user = userMapper.selectUserById(1);
            System.out.println(user);
            // 提交事务
            sqlSession.commit();
        } catch (Exception e)
        {
            // 出错回滚事务
            sqlSession.rollback();
            e.printStackTrace();
        } finally
        {
            // 关闭会话
            if(sqlSession != null)
                sqlSession.close();
        }
    }
}

运行效果:

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DEBUG [main] Cache Hit Ratio [mapper.UserMapper]: 0.0
DEBUG [main] ==>  Preparing: select * from tb_user where id=? 
DEBUG [main] ==> Parameters: 1(Integer)
DEBUG [main] <==      Total: 1
User [id=1, name=小明, sex=男, age=21]
-----------------------------------------------
DEBUG [main] Cache Hit Ratio [mapper.UserMapper]: 0.5
User [id=1, name=小明, sex=男, age=21]

在关闭第一个sqlSession时,查询的信息会保存到二级缓存中,重新获取sqlSession,再次执行相同的查询时,二级缓存中已经后该数据,不需要再次执行sql语句,而是从二级缓存中返回数据.

按id删除

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package test;

import java.util.List;
import org.apache.ibatis.session.SqlSession;
import domain.User;
import fractory.SqlSessionFratoryTools;
import mapper.UserMapper;

public class DeleteUserTest{
    public static void main(String[] args)
    {
        SqlSession sqlSession = null;
        try
        {
            // 加载mybatis-config.xml,获取SqlSession实例
            sqlSession = SqlSessionFratoryTools.getSqlSession();
            // 获取mapper接口代理对象
            UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
            List<User> users = userMapper.selectAllUsers();
            users.forEach(user-> System.out.println(user));
            System.out.println("----------------------------------------");
            // userMapper.deleteUserById(users.get(0).getId());
            sqlSession.close();
            System.out.println("----------------------------------------");
            // 再次加载mybatis-config.xml,获取SqlSession实例
            sqlSession = SqlSessionFratoryTools.getSqlSession();
            // 再次获取mapper接口代理对象
            userMapper = sqlSession.getMapper(UserMapper.class);
            users = userMapper.selectAllUsers();
            users.forEach(user-> System.out.println(user));
            // 提交事务
            sqlSession.commit();
        } catch (Exception e)
        {
            // 出错回滚事务
            sqlSession.rollback();
            e.printStackTrace();
        } finally
        {
            // 关闭会话
            if(sqlSession != null)
                sqlSession.close();
        }

    }
}

运行效果:

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DEBUG [main] Cache Hit Ratio [mapper.UserMapper]: 0.0
DEBUG [main] ==>  Preparing: select * from tb_user 
DEBUG [main] ==> Parameters: 
DEBUG [main] <==      Total: 5
User [id=1, name=小明, sex=男, age=21]
User [id=2, name=小王, sex=男, age=22]
User [id=3, name=小丽, sex=女, age=18]
User [id=4, name=小芳, sex=女, age=18]
User [id=5, name=小王, sex=男, age=22]
----------------------------------------
----------------------------------------
DEBUG [main] Cache Hit Ratio [mapper.UserMapper]: 0.5
User [id=1, name=小明, sex=男, age=21]
User [id=2, name=小王, sex=男, age=22]
User [id=3, name=小丽, sex=女, age=18]
User [id=4, name=小芳, sex=女, age=18]
User [id=5, name=小王, sex=男, age=22]

测试并没有执行删除语句,第二次查询时从二级缓存从返回数据.
取消删除语句的注释,再吃执行,运行效果如下:

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DEBUG [main] Cache Hit Ratio [mapper.UserMapper]: 0.0
DEBUG [main] ==>  Preparing: select * from tb_user 
DEBUG [main] ==> Parameters: 
DEBUG [main] <==      Total: 5
User [id=1, name=小明, sex=男, age=21]
User [id=2, name=小王, sex=男, age=22]
User [id=3, name=小丽, sex=女, age=18]
User [id=4, name=小芳, sex=女, age=18]
User [id=5, name=小王, sex=男, age=22]
----------------------------------------
DEBUG [main] ==>  Preparing: delete from tb_user where id=? 
DEBUG [main] ==> Parameters: 1(Integer)
DEBUG [main] <==    Updates: 1
----------------------------------------
DEBUG [main] Cache Hit Ratio [mapper.UserMapper]: 0.0
DEBUG [main] ==>  Preparing: select * from tb_user 
DEBUG [main] ==> Parameters: 
DEBUG [main] <==      Total: 5
User [id=1, name=小明, sex=男, age=21]
User [id=2, name=小王, sex=男, age=22]
User [id=3, name=小丽, sex=女, age=18]
User [id=4, name=小芳, sex=女, age=18]
User [id=5, name=小王, sex=男, age=22]

DML语句(insert,update,delete)会清空缓存,所以第二次查询时缓存中没有信息,需要再次执行SQL语句从数据库中查询信息.

原文链接: 11.4 注解使用二级缓存