mybatis的二级缓存使用

阳光穿透心脏的1/2处 2023-02-15 13:50 13阅读 0赞

我们首先要知道mybatis中的一级缓存是在没有关闭session的时候，执行相同的select时候，二次以后的查询不会发送select语句至数据库，以减少对数据库的联机操作。

二级缓存是建立了2个session以后执行相同的select语句后依然也不会再数据库执行select语句，而内容依然从缓存中读取出来。  
我们看一下如果使用mybatis的二级缓存；希望大家可以仔细阅读，里面有一些注意细节，这些细节对于初学者很有帮助。  
（1）在mybatis的核心配置文件中开启二级环境配置  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poYW5nNjEzMjMyNg_size_16_color_FFFFFF_t_70]

(2)pojo映射类实现Serializable接口

package com.zxf.pojo;
    
    
    
    import java.io.Serializable;
    
    
    public class Employee implements Serializable{ 
        private String emp_no;
        private String emp_name;
        private String dept_id;
        private String emp_gender;
    
        public String getEmp_gender() { 
            return emp_gender;
        }
    
        public void setEmp_gender(String emp_gender) { 
            this.emp_gender = emp_gender;
        }
    
        
    
        public String getDept_id() { 
            return dept_id;
        }
    
        public void setDept_id(String dept_id) { 
            this.dept_id = dept_id;
        }
    
       
    
        public String getEmp_name() { 
            return emp_name;
        }
    
        public void setEmp_name(String emp_name) { 
            this.emp_name = emp_name;
        }
    
        public String getEmp_no() { 
    
            return emp_no;
        }
    
        public void setEmp_no(String emp_no) { 
            this.emp_no = emp_no;
        }
    }

(3) Mapper数据库操作接口

public interface EmployeeMapper { 
     public List<Employee> getAll4();
    }

(4) Mapper接口映射配置文件

<?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.zxf.mapper.EmployeeMapper">
        
        <cache eviction="FIFO" flushInterval="6000" readOnly="false" size="1024"></cache>
          <select id="getAll4" resultType="emp">
            select  <include refid="emp_1"/>    from employee_basic
        </select>
        </mapper>

(5)测试类

@Test
        public void test2() throws Exception{ 
            InputStream is= Resources.getResourceAsStream("mybatis_config.xml");
            SqlSessionFactory factory=new SqlSessionFactoryBuilder().build(is);
            SqlSession session1=factory.openSession();
            SqlSession session2=factory.openSession();
            EmployeeMapper mapper1 = session1.getMapper(EmployeeMapper.class);
            EmployeeMapper mapper2=session2.getMapper(EmployeeMapper.class);
            List<Employee> all_1 = mapper1.getAll4();
            List<Employee> all_2 = mapper2.getAll4();
            for(Employee e:all_1){ 
                System.out.println(e.getEmp_name()+":"+e.getEmp_no());
            }
             session1.close();
            /* 这里要记住一个地方，第二次查询必须要等第一次的session关闭以后才可以。 否则二级缓存没有作用，依然还会执行二次select语句发送至数据库 */
    
            for(Employee e:all_2){ 
                System.out.println(e.getEmp_name()+"===>"+e.getEmp_no());
            }
             session2.close();
    
        }

(6)运行结果1  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poYW5nNjEzMjMyNg_size_16_color_FFFFFF_t_70 1]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poYW5nNjEzMjMyNg_size_16_color_FFFFFF_t_70 2]  
运行结果2  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poYW5nNjEzMjMyNg_size_16_color_FFFFFF_t_70 3]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poYW5nNjEzMjMyNg_size_16_color_FFFFFF_t_70 4]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poYW5nNjEzMjMyNg_size_16_color_FFFFFF_t_70 5]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poYW5nNjEzMjMyNg_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/20200605213039105.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poYW5nNjEzMjMyNg==,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poYW5nNjEzMjMyNg_size_16_color_FFFFFF_t_70 1]: https://img-blog.csdnimg.cn/20200605213626725.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poYW5nNjEzMjMyNg==,size_16,color_FFFFFF,t_70
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