24.MyBatis缓存

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Hibernate和MyBatis缓存对比

框架 缓存 作用范围 默认开启
Hibernate 一级缓存 Session 是
二级缓存 SessionFactory 否
MyBatis 一级缓存 SqlSession 是
二级缓存 SqlSessionFactory 否

MyBatis缓存

MyBatis一级缓存

在SqlSession范围内，当查询相同的对象时，会使用缓存中的数据，而不会再次查询。

只要SqlSession不关闭，使用SqlSession去查询同一个对象，就只会执行一条sql

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package com.course.test;

import java.util.List;

import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import com.course.dao.DepartmentDao;
import com.course.util.MyBatisUtil;
import com.course.vo.Department;

public class DepartmentTest {

	private SqlSession sqlSession = MyBatisUtil.openSqlSession();
	private DepartmentDao departmentDao = sqlSession.getMapper(DepartmentDao.class);
	
	@Test
	public void getDepartmentById() {
		Integer departmentId = 1;
		Department department1 = departmentDao.getDepartmentById(departmentId);
		Department department2 = departmentDao.getDepartmentById(departmentId);
		
		System.out.println(department1);
		System.out.println(department2);
		
	}
}
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DEBUG [main] - ==>  Preparing: select * from department where department_id = ? 
DEBUG [main] - ==> Parameters: 1(Integer)
DEBUG [main] - <==      Total: 1
Department [department_id=1, department_name=Retail Department, location=5 floor, employees=null]
Department [department_id=1, department_name=Retail Department, location=5 floor, employees=null]

只执行了一次查询

MyBatis二级缓存

作用范围为SqlSessionFactory，需要手动启用。

Mapper.xml中添加<cache></cache>标签，该Mapper.xml中的所有sql都会开启二级缓存，不仅<select>，包括<insert><update><delete>都会开启二级缓存。

如果想要让某个sql不开启二级缓存，添加属性useCache="false"，默认值为true

Mapper.xml

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<?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.course.dao.abc.UserDao">
	
	<cache></cache>

	<insert id="addUserXml" parameterType="com.course.vo.User">
		insert into user(name, age, address, birthday) 
			values(#{name}, #{age}, #{address}, #{birthday})
	</insert>
	
	<update id="updateUser" parameterType="com.course.vo.User">
		update user set name=#{name}, age=#{age}, address=#{address}, birthday=#{birthday}
			where id=#{id}
	</update>
	
	<delete id="deleteUser" parameterType="int">
		delete from user 
			where id=#{val}
	</delete>
	
	<select id="getUserById" parameterType="int" resultType="com.course.vo.User">
		select * from user where id=#{val}
	</select>
	
	<select id="getAllUser" useCache="false" resultType="com.course.vo.User">
		select * from user
	</select>
</mapper>

mybatis.cfg.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">
  
<!-- MyBatis的整体配置 -->
<configuration>

	<settings>
		<!-- 开启二级缓存 -->
		<setting name="cacheEnabled" value="true"/>
	</settings>
    
</configuration>

MyBatis和Hibernate的比较

Hibernate: 自动生成表，生成关系，对于单表的CRUD，不用写sql和hql

mybatis: 对于多表连接查询等等更加方便，因为sql写起来简单

Mybatis半自动化模式操作数据，hibenate完全面向对象操作数据

Mybatis运行的性能高于hibernate的性能

Mybatis开发速度低于hibernate的开发速度

Mybatis应用在互联网项目的开发，Hibernate用在传统的MIS(Management Information System，管理信息系统)系统开发