11.4 注解使用二级缓存

发表于 2019-06-18 更新于 2020-06-05 分类于 4 Spring+Mybatis企业应用实战(第2版) ，第11章 MyBatis的注解配置， 11.4 注解使用二级缓存 Waline：本文字数： 12k 阅读时长 ≈ 11 分钟

11.4 注解使用二级缓存

项目结构

展开/折叠

G:\workspace_web2\MyATwoLevelCacheTest
├─src\
│ ├─db.properties
│ ├─domain\
│ │ └─User.java
│ ├─fractory\
│ │ └─SqlSessionFactoryTools.java
│ ├─log4j.xml
│ ├─mapper\
│ │ └─UserMapper.java
│ ├─mybatis-config.xml
│ ├─tb_user.sql
│ └─test\
│   ├─DeleteUserTest.java
│   └─SelectTest.java
└─WebContent\
  ├─META-INF\
  │ └─MANIFEST.MF
  └─WEB-INF\
    └─lib\
      ├─commons-logging-1.2.jar
      ├─log4j-1.2.17.jar
      ├─log4j-api-2.3.jar
      ├─log4j-core-2.3.jar
      ├─mybatis-3.4.5.jar
      └─mysql-connector-java-5.1.44-bin.jar

数据库表

/MyATwoLevelCacheTest/src/tb_user.sql

-- 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`)
);
-- 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

/MyATwoLevelCacheTest/src/db.properties

#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

<?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

<?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

/MyATwoLevelCacheTest/src/domain/User.java

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

/MyATwoLevelCacheTest/src/mapper/UserMapper.java

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 用户记录
     */
    @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 用户列表
     */
    @Select("select * from tb_user")
    @Options(useCache = true)
    List<User> selectAllUsers();

    /**
     * 根据id删除用户信息.
     * 
     * @param id 主键
     */
    @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

@CacheNamespace注解用来配置二级缓存,如下所示:

@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

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 SqlSessionFactoryTools {
    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SelectTest.java

/MyATwoLevelCacheTest/src/test/SelectTest.java

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:

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,由于二级缓存中已经有该数据,所以不需要再次执行sql语句,而是直接从二级缓存中返回数据.

按id删除DeleteUserTest.java

/MyATwoLevelCacheTest/src/test/DeleteUserTest.java

package test;

import java.util.List;
import org.apache.ibatis.session.SqlSession;
import domain.User;
import fractory.SqlSessionFactoryTools;
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 = SqlSessionFactoryTools.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.commit();
            sqlSession.close();
            System.out.println("----------------------------------------");
            // 再次加载mybatis-config.xml,获取SqlSession实例
            sqlSession = SqlSessionFactoryTools.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:

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:

// 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.commit();
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));

再次执行,运行效果如下:

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: 4
  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语句会清空缓存

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.