缓存即为存在内存中的临时数据.将用户经常查询的数据存放在缓存(内存)中,用户去查询数据就不用去每次去数据库中查询,而是去缓存中查询,从而提高了查询的效率,解决了高并发系统的性能问题.MyBatis提供了两种缓存机制：一级缓存（本地）和二级缓存（全局）
1、默认情况下，只有一级缓存( SqlSession级别的缓存也称为本地缓存)开启。
2、二级缓存需要手动开启和配置，他是基于namespace级别的缓存。
3、为了提高扩展性。MyBatis定义了缓存接口Cache。我们可以通过实现Cache接口来自定义二级缓存
1. 基础环境
1.1 数据库准备
USE mybatis;
# 创建一个名称为tb_book的表
CREATE TABLE tb_book(
id INT PRIMARY KEY AUTO_INCREMENT,
name VARCHAR(255),
price double,
author VARCHAR(40)
);
# 插入3条数据
INSERT INTO tb_book(name,price,author) VALUES('Java基础入门',45.0,'Liy');
INSERT INTO tb_book(name,price,author) VALUES('Java基础案例教程',48.0,'Tom');
INSERT INTO tb_book(name,price,author) VALUES('JavaWeb程序设计任务教程',50.0,'Jack');
1.2 Idea环境搭建
1.2.1 创建一个cache的module
1.2.2 在pom.xml中引入所需要的包
mybatis, mysql-connector-java, junit, log4j, lombok
<?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">
<parent>
<artifactId>mybatis-series</artifactId>
<groupId>com.biem</groupId>
<version>1.0-SNAPSHOT</version>
</parent>
<modelVersion>4.0.0</modelVersion>
<artifactId>cache</artifactId>
<properties>
<maven.compiler.source>8</maven.compiler.source>
<maven.compiler.target>8</maven.compiler.target>
</properties>
<dependencies>
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
</dependency>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<scope>test</scope>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
</dependency>
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
</dependency>
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.16</version>
</dependency>
</dependencies>
</project>
1.2.3 创建包：com.biem.pojo, com.biem.mapper, com.biem.util
1.2.4 在resource下添加配置文件
1.2.4.1 添加配置文件jdbc.properties
jdbc.driver=com.mysql.cj.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/mybatis?serverTimezone=UTC
jdbc.username=root
jdbc.password=root
1.2.4.2 添加配置文件log4j.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">
<appender name="STDOUT" class="org.apache.log4j.ConsoleAppender">
<param name="Encoding" value="UTF-8"/>
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%-5p %d{MM-dd HH:mm:ss,SSS} %m (%F:%L) \n"/>
</layout>
</appender>
<logger name="java.sql">
<level value="debug"/>
</logger>
<logger name="org.apache.ibatis">
<level value="info"/>
</logger>
<root>
<level value="debug"/>
<appender-ref ref="STDOUT"/>
</root>
</log4j:configuration>
1.2.4.3 添加MyBatis的核心配置类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">
<configuration>
<!--引入properties文件-->
<properties resource="jdbc.properties"></properties>
<!--将下划线映射为驼峰-->
<settings>
<setting name="mapUnderscoreToCamelCase" value="true"/>
</settings>
<!--设置类型别名-->
<typeAliases>
<package name="com.biem.pojo"/>
</typeAliases>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="${jdbc.driver}"/>
<property name="url" value="${jdbc.url}"/>
<property name="username" value="${jdbc.username}"/>
<property name="password" value="${jdbc.password}"/>
</dataSource>
</environment>
</environments>
<!-- 引入映射文件 -->
<mappers>
<package name="com.biem.mapper"/>
</mappers>
</configuration>
1.2.4.4 创建映射文件所在的目录
1.2.5 添加工具类com.biem.util.MyBatisUtil.java
package com.biem.util;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import java.io.IOException;
import java.io.InputStream;
/**
* ClassName: MybatisUtil
* Package: com.biem.util
* Description:
*
* @Create 2023/4/5 22:23
* @Version 1.0
*/
public class MyBatisUtil {
//利用static(静态)属于类不属于对象,且全局唯一
private static SqlSessionFactory sqlSessionFactory = null;
//利用静态块在初始化类时实例化sqlSessionFactory
static {
InputStream is= null;
try {
is = Resources.getResourceAsStream("mybatis-config.xml");
sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
} catch (IOException e) {
e.printStackTrace();
throw new ExceptionInInitializerError(e);
}
}
/**
* openSession 创建一个新的SqlSession对象
* @return SqlSession对象
*/
public static SqlSession openSession(boolean autoCommit){
return sqlSessionFactory.openSession(autoCommit);
}
public static SqlSession openSession(){
return sqlSessionFactory.openSession();
}
/**
* 释放一个有效的SqlSession对象
* @param session 准备释放SqlSession对象
*/
public static void closeSession(SqlSession session){
if(session != null){
session.close();
}
}
}
1.2.6 实体类com.biem.pojo.Book.java
package com.biem.pojo;
import lombok.*;
/**
* ClassName: Book
* Package: com.biem.pojo
* Description:
*
* @Create 2023/5/18 7:58
* @Version 1.0
*/
@Getter
@Setter
@ToString
@NoArgsConstructor
@AllArgsConstructor
public class Book {
private Integer id;
private String name;
private Integer price;
private String author;
}
1.2.7 mapper接口
package com.biem.mapper;
/**
* ClassName: BookMapper
* Package: com.biem.mapper
* Description:
*
* @Create 2023/5/18 8:01
* @Version 1.0
*/
public interface BookMapper {
}
1.2.7 mapper映射文件
<?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.biem.mapper.BookMapper">
<!-- sql语句要和接口的方法名保持一致 -->
</mapper>
2. 一级缓存（本地）
MyBatis的一级缓存是SqlSession级别的缓存。
如果同一个SqlSession对象多次执行完全相同的SQL语句，在第一次执行完成后，MyBatis会将查询的结果写入到一级缓存中。此后如果程序没有执行插入、更新、删除操作。当第二次执行相同的查询语句时，MyBatis会直接读取一级缓存中的数据，而不在去数据库查询，从而提高了数据库的查询效率。
测试案例1：
从数据库tb_book查询id为1的图书信息的时候，当第一次查询后会将结果写入MyBatis的一级缓存，当程序第二次查询id为1的图书信息，MyBatis会直接从一级缓存中读取。
2.1 接口添加方法
package com.biem.mapper;
import com.biem.pojo.Book;
public interface BookMapper {
public Book findBookById(Integer id);
}
2.2 映射文件添加实现
<?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.biem.mapper.BookMapper">
<!-- sql语句要和接口的方法名保持一致 -->
<!--public Book findBookById(Integer id);-->
<select id="findBookById" parameterType="Integer" resultType="Book">
select * from tb_book where id=#{id}
</select>
</mapper>
2.3 测试方法
package com.biem.test;
import com.biem.mapper.BookMapper;
import com.biem.pojo.Book;
import com.biem.util.MyBatisUtil;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
/**
* ClassName: UserTest
* Package: com.biem.test
* Description:
*
* @Create 2023/5/18 8:44
* @Version 1.0
*/
public class UserTest {
@Test
public void findBookById(){
SqlSession session = MyBatisUtil.openSession();
BookMapper mapper = session.getMapper(BookMapper.class);
Book book = mapper.findBookById(1);
System.out.println("book = " + book);
session.close();
}
@Test
public void testCache1(){
SqlSession session = MyBatisUtil.openSession();
BookMapper mapper1 = session.getMapper(BookMapper.class);
Book book1 = mapper1.findBookById(1);
System.out.println("book1 = " + book1);
BookMapper mapper2 = session.getMapper(BookMapper.class);
Book book2 = mapper2.findBookById(1);
System.out.println("book1 = " + book2);
session.close();
}
}
2.4 结果分析
findBookById输出如下：
DEBUG 05-18 09:07:47,909 ==> Preparing: select * from tb_book where id=? (BaseJdbcLogger.java:137)
DEBUG 05-18 09:07:47,986 ==> Parameters: 1(Integer) (BaseJdbcLogger.java:137)
DEBUG 05-18 09:07:48,047 <== Total: 1 (BaseJdbcLogger.java:137)
book = Book(id=1, name=Java基础入门, price=45, author=Liy)
testCache1输出如下
DEBUG 05-18 09:07:48,056 ==> Preparing: select * from tb_book where id=? (BaseJdbcLogger.java:137)
DEBUG 05-18 09:07:48,057 ==> Parameters: 1(Integer) (BaseJdbcLogger.java:137)
DEBUG 05-18 09:07:48,059 <== Total: 1 (BaseJdbcLogger.java:137)
book1 = Book(id=1, name=Java基础入门, price=45, author=Liy)
book1 = Book(id=1, name=Java基础入门, price=45, author=Liy)
从上述输出可以看出testCache1只是查询了一次，第二次查询的时候并没有连接数据库
testCache1fail输出如下
DEBUG 05-18 09:14:30,875 ==> Preparing: select * from tb_book where id=? (BaseJdbcLogger.java:137)
DEBUG 05-18 09:14:30,953 ==> Parameters: 1(Integer) (BaseJdbcLogger.java:137)
DEBUG 05-18 09:14:31,015 <== Total: 1 (BaseJdbcLogger.java:137)
book1 = Book(id=1, name=Java基础入门, price=45, author=Liy)
DEBUG 05-18 09:14:31,059 ==> Preparing: select * from tb_book where id=? (BaseJdbcLogger.java:137)
DEBUG 05-18 09:14:31,060 ==> Parameters: 1(Integer) (BaseJdbcLogger.java:137)
DEBUG 05-18 09:14:31,065 <== Total: 1 (BaseJdbcLogger.java:137)
book1 = Book(id=1, name=Java基础入门, price=45, author=Liy)
3. 二级缓存（全局）
3.1 开启缓存前配置
3.1.1 实体类实现Serializable 接口
package com.biem.pojo;
import lombok.*;
import java.io.Serializable;
@Getter
@Setter
@ToString
@NoArgsConstructor
@AllArgsConstructor
public class Book implements Serializable {
private Integer id;
private String name;
private Integer price;
private String author;
}
3.1.2 mybatis-config.xml中开启二级缓存全局配置
mybatis-config.xml中添加
<settings>
<setting name="cacheEnabled" value="true"/>
</settings>
3.1.3 开启当前mapper下的二级缓存BookMapper.xml
BookMapper.xml添加
<cache></cache>
3.2 添加测试方法UserTest.java
@Test
public void testCache2_0(){
SqlSession session1 = MyBatisUtil.openSession();
BookMapper mapper1 = session1.getMapper(BookMapper.class);
Book book1 = mapper1.findBookById(1);
System.out.println("book1 = " + book1);
SqlSession session2 = MyBatisUtil.openSession();
BookMapper mapper2 = session2.getMapper(BookMapper.class);
Book book2 = mapper2.findBookById(1);
System.out.println("book1 = " + book2);
session1.close();
session2.close();
}
@Test
public void testCache2_1(){
SqlSession session1 = MyBatisUtil.openSession();
BookMapper mapper1 = session1.getMapper(BookMapper.class);
Book book1 = mapper1.findBookById(1);
System.out.println("book1 = " + book1);
session1.close();
SqlSession session2 = MyBatisUtil.openSession();
BookMapper mapper2 = session2.getMapper(BookMapper.class);
Book book2 = mapper2.findBookById(1);
System.out.println("book1 = " + book2);
session2.close();
}
3.3结果分析
testCache2_1进行了一次查询，结果如下：
DEBUG 05-18 09:40:00,228 Cache Hit Ratio [com.biem.mapper.BookMapper]: 0.0 (LoggingCache.java:60)
DEBUG 05-18 09:40:02,793 ==> Preparing: select * from tb_book where id=? (BaseJdbcLogger.java:137)
DEBUG 05-18 09:40:02,867 ==> Parameters: 1(Integer) (BaseJdbcLogger.java:137)
DEBUG 05-18 09:40:02,944 <== Total: 1 (BaseJdbcLogger.java:137)
book1 = Book(id=1, name=Java基础入门, price=45, author=Liy)
WARN 05-18 09:40:02,960 As you are using functionality that deserializes object streams, it is recommended to define the JEP-290 serial filter. Please refer to https://docs.oracle.com/pls/topic/lookup?ctx=javase15&id=GUID-8296D8E8-2B93-4B9A-856E-0A65AF9B8C66 (SerialFilterChecker.java:46)
DEBUG 05-18 09:40:02,968 Cache Hit Ratio [com.biem.mapper.BookMapper]: 0.5 (LoggingCache.java:60)
book1 = Book(id=1, name=Java基础入门, price=45, author=Liy)
testCache2_2进行了一次查询，结果如下：
DEBUG 05-18 09:41:38,669 Cache Hit Ratio [com.biem.mapper.BookMapper]: 0.0 (LoggingCache.java:60)
DEBUG 05-18 09:41:41,356 ==> Preparing: select * from tb_book where id=? (BaseJdbcLogger.java:137)
DEBUG 05-18 09:41:41,433 ==> Parameters: 1(Integer) (BaseJdbcLogger.java:137)
DEBUG 05-18 09:41:41,504 <== Total: 1 (BaseJdbcLogger.java:137)
book1 = Book(id=1, name=Java基础入门, price=45, author=Liy)
WARN 05-18 09:41:41,523 As you are using functionality that deserializes object streams, it is recommended to define the JEP-290 serial filter. Please refer to https://docs.oracle.com/pls/topic/lookup?ctx=javase15&id=GUID-8296D8E8-2B93-4B9A-856E-0A65AF9B8C66 (SerialFilterChecker.java:46)
DEBUG 05-18 09:41:41,529 Cache Hit Ratio [com.biem.mapper.BookMapper]: 0.5 (LoggingCache.java:60)
book2 = Book(id=1, name=Java基础入门, price=45, author=Liy)
DEBUG 05-18 09:41:41,531 Cache Hit Ratio [com.biem.mapper.BookMapper]: 0.6666666666666666 (LoggingCache.java:60)
book3 = Book(id=1, name=Java基础入门, price=45, author=Liy)
testCache2_0和testCache1一样的内容，输出结果如下：
DEBUG 05-18 09:39:11,470 Cache Hit Ratio [com.biem.mapper.BookMapper]: 0.0 (LoggingCache.java:60)
DEBUG 05-18 09:39:14,368 ==> Preparing: select * from tb_book where id=? (BaseJdbcLogger.java:137)
DEBUG 05-18 09:39:14,501 ==> Parameters: 1(Integer) (BaseJdbcLogger.java:137)
DEBUG 05-18 09:39:14,567 <== Total: 1 (BaseJdbcLogger.java:137)
book1 = Book(id=1, name=Java基础入门, price=45, author=Liy)
DEBUG 05-18 09:39:14,580 Cache Hit Ratio [com.biem.mapper.BookMapper]: 0.0 (LoggingCache.java:60)
DEBUG 05-18 09:39:14,656 ==> Preparing: select * from tb_book where id=? (BaseJdbcLogger.java:137)
DEBUG 05-18 09:39:14,656 ==> Parameters: 1(Integer) (BaseJdbcLogger.java:137)
DEBUG 05-18 09:39:14,659 <== Total: 1 (BaseJdbcLogger.java:137)
book1 = Book(id=1, name=Java基础入门, price=45, author=Liy)
testCache2_0依然进行了两次查询，session.close()执行之前并没有刷新缓存。
