Day34——MyBatis一级缓存的使用

我就是我 2023-07-04 15:42 9阅读 0赞

# 一. 例子 #

EmployeeMapperCache.java

package com.atguigu.mybatis.dao;
    
    import com.atguigu.mybatis.beans.Employee;
    
    public interface EmployeeMapperCache { 
    
    	public Employee selectEmployeeById(Integer id);
    	
    }

EmployeeMapperCache.xml

<?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.atguigu.mybatis.dao.EmployeeMapperCache">
    	  
    	  
    	  <select id="selectEmployeeById" resultType="com.atguigu.mybatis.beans.Employee">
    	      select id, last_name, email, gender from tbl_employee where id = #{id}
    	  </select>
    	  
    	
    </mapper>

TestMyBatisCache.java

package com.atguigu.mybatis.test;
    
    import java.io.InputStream;
    import java.util.ArrayList;
    import java.util.List;
    
    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 org.junit.Test;
    
    import com.atguigu.mybatis.beans.Employee;
    import com.atguigu.mybatis.dao.EmployeeMapperCache;
    import com.atguigu.mybatis.dao.EmployeeMapperDynamicSQL;
    
    public class TestMyBatisCache { 
    
        /** * 一级缓存（本地缓存）： * 1. 一级缓存默认是开启的 * 2. 一级缓存是SqlSession级别的缓存。每一个SqlSession对象都有自己的一级缓存 * 3. 一级缓存的工作机制： * 一个SqlSession对象第一次查数据，会从数据库中把对应的数据查询到， * 并且会将查询到的数据保存到当前SqlSession对象的一级缓存中。再使用 * 当前的SqlSession对象进行后续的查询相同的数据，都可以从一级缓存中获取到对应 * 的数据。 * 4. 实际上一级缓存就是一个Map。key：hashCode+查询的SqlId+编写的sql查询语句+参数 * */
    	@Test
    	public void testFirstLevelCache() throws Exception{ 
    		 SqlSessionFactory ssf = getSqlSessionFactory();
    		 SqlSession session = ssf.openSession();
    		 
    		 try { 
    			 EmployeeMapperCache mapper = session.getMapper(EmployeeMapperCache.class);
    			 
                 Employee employee1 = mapper.selectEmployeeById(1001);
                 System.out.println("employee1:" + employee1);
    			 
                 System.out.println("------------------------------------------");
                 
                 Employee employee2 = mapper.selectEmployeeById(1001);
                 System.out.println("employee2:" + employee2);
                 
                 session.commit();
    			 
    		} finally { 
    			// TODO: handle finally clause
    			session.close();
    		}
    	}
    	
    	
    	
    	public SqlSessionFactory getSqlSessionFactory() throws Exception { 
    		String resource = "mybatis-config.xml"; 
    		InputStream inputStream = 
    				Resources.getResourceAsStream(resource); 
    		SqlSessionFactory sqlSessionFactory = 
    				new SqlSessionFactoryBuilder().build(inputStream);
    		return sqlSessionFactory;
    	}
    	
    	
    }