MyBatis一级缓存实战

梦里梦外; 2021-07-24 12:25 445阅读 0赞

**一 领域模型**

package org.fkit.domain;
    import java.io.Serializable;
    /**
    *
    * 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`)
    )
    */
    public class User implements Serializable{
         
         private static final long serialVersionUID = 1L;
         
         private Integer id;
         private String name;
         private String sex;
         private Integer age;
         
         public User() {
               super();
               // TODO Auto-generated constructor stub
         }
         
         public User( String name, String sex, Integer age) {
               super();
               this.name = name;
               this.sex = sex;
               this.age = age;
         }
         public Integer getId() {
               return id;
         }
         public void setId(Integer id) {
               this.id = id;
         }
         public String getName() {
               return name;
         }
         public void setName(String name) {
               this.name = name;
         }
         public String getSex() {
               return sex;
         }
         public void setSex(String sex) {
               this.sex = sex;
         }
         public Integer getAge() {
               return age;
         }
         public void setAge(Integer age) {
               this.age = age;
         }
         @Override
         public String toString() {
               return "User [id=" + id + ", name=" + name + ", sex="  + sex + ", age="
                         + age + "]";
         }
         
         
    }

**二 会话工厂**

package org.fkit.factory;
    
    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 FKSqlSessionFactory {
        
        private static SqlSessionFactory sqlSessionFactory = null;
        
        // 初始化创建SqlSessionFactory对象
        static{
            try (// 读取mybatis-config.xml文件
                    InputStream is = Resources.getResourceAsStream("mybatis-config.xml");
                ){
                sqlSessionFactory = new SqlSessionFactoryBuilder()
                        .build(is);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        
        // 获取SqlSession对象的静态方法
        public static SqlSession getSqlSession(){
            return sqlSessionFactory.openSession();
        }
    
        // 获取SqlSessionFactory的静态方法
        public static SqlSessionFactory getSqlSessionFactory() {
            return sqlSessionFactory;
        }
    
    }

**三 mapper**

1 UserMapper

package org.fkit.mapper;
    
    import java.util.List;
    import org.fkit.domain.User;
    
    public interface UserMapper {
        
        // 根据id查询User
        User selectUserById(Integer id);
        
        // 查询所有User
        List<User> selectAllUser();
        
        // 根据id删除User
        void deleteUserById(Integer id);
    
    }

2 UserMapper.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="org.fkit.mapper.UserMapper">
         
      
      <select id="selectUserById" parameterType="int"
      resultType="org.fkit.domain.User">
          SELECT * FROM TB_USER WHERE id = #{id}
      </select>
      
      
      <select id="selectAllUser" resultType="org.fkit.domain.User">
          SELECT * FROM TB_USER
      </select>
      
      
      <delete id="deleteUserById" parameterType="int">
          DELETE FROM TB_USER WHERE id = #{id}
      </delete>
      
    </mapper>

**四 配置文件**

1 db.properties

driver=com.mysql.jdbc.Driver
    url=jdbc:mysql://127.0.0.1:3306/mybatis
    username=root
    password=123456

2 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">  
            <layout class="org.apache.log4j.PatternLayout">  
                <param name="ConversionPattern" value="%5p [%t] %m%n"  />  
            </layout>  
        </appender>   
         <logger name="org.fkit.mapper">  
            <level value="DEBUG" />  
        </logger>
        <root>  
            <level value="ERROR" />  
            <appender-ref ref="STDOUT" />  
        </root>  
    </log4j:configuration>

3 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>
         <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 resource="org/fkit/mapper/UserMapper.xml"/>
      </mappers>
    </configuration>

**五 测试**

package org.fkit.test;
    
    import org.apache.ibatis.session.SqlSession;
    import org.fkit.domain.User;
    import org.fkit.factory.FKSqlSessionFactory;
    import org.fkit.mapper.UserMapper;
    
    public class OneLevelCacheTest {
    
        public static void main(String[] args)  {
    
            // 定义SqlSession变量
            SqlSession sqlSession = null;
            try {
                // 创建SqlSession实例
                sqlSession = FKSqlSessionFactory.getSqlSession();
                OneLevelCacheTest t = new OneLevelCacheTest();
    
    //            t.testCache1(sqlSession);
    //            t.testCache2(sqlSession);
    //            t.testCache3(sqlSession);
                t.testCache4();
                
                // 提交事务
                sqlSession.commit();
            } catch (Exception e) {
                // 回滚事务
                sqlSession.rollback();
                e.printStackTrace();
            }finally {
                // 关闭SqlSession
                if(sqlSession != null)
                    sqlSession.close();
            }
        }
        
         /*
          * 一级缓存: 也就Session级的缓存(默认开启)
          */
        public void testCache1 (SqlSession sqlSession){
            // 获得UserMapping对象
            UserMapper um = sqlSession.getMapper(UserMapper.class);
            // 查询id为1的User对象，会执行select语句
            User user = um.selectUserById(1);
            System.out.println(user);
            // 再次查询id为1的User对象,因为是同一个SqlSession,所以会从之前的一级缓存中查找数据
            User user2 = um.selectUserById(1);
            System.out.println(user2);
        }
        
        // 测试一级缓存执行DML语句并提交
        public void testCache2 (SqlSession sqlSession){
            // 获得UserMapping对象
            UserMapper um = sqlSession.getMapper(UserMapper.class);
            // 查询id为1的User对象，会执行select语句
            User user = um.selectUserById(1);
            System.out.println(user);
            // 执行delete操作
            um.deleteUserById(5);
            // commit提交
            sqlSession.commit();
            // 再次查询id为1的User对象,因为DML操作会清空SqlSession缓存,所以会再次执行select语句
            User user2 = um.selectUserById(1);
            System.out.println(user2);
        }
        
        // 测试一级缓存clearCache
        public void testCache3 (SqlSession sqlSession){
            // 获得UserMapping对象
            UserMapper um = sqlSession.getMapper(UserMapper.class);
            // 查询id为1的User对象，会执行select语句
            User user = um.selectUserById(1);
            System.out.println(user);
            // 清空一级缓存
            sqlSession.clearCache();
            // 再次获得UserMapping对象
            um = sqlSession.getMapper(UserMapper.class);
            // 再次访问，因为SqlSession一级缓存已经清空,所以会再次执行select语句
            User user2 = um.selectUserById(1);
            System.out.println(user2);
        }
        
        // 测试一级缓存close
        public void testCache4 (){
            // 使用工厂类获得SqlSession对象
            SqlSession sqlSession = FKSqlSessionFactory.getSqlSession();
            // 获得UserMapping对象
            UserMapper um = sqlSession.getMapper(UserMapper.class);
            // 查询id为1的User对象，会执行select语句
            User user = um.selectUserById(1);
            System.out.println(user);
            // 关闭一级缓存
            sqlSession.close();
            // 再次访问,重新获取一级缓存，然后才能查找数据，否则会抛出异常
            SqlSession sqlSession2 = FKSqlSessionFactory.getSqlSession();
            // 再次获得UserMapping对象
            um = sqlSession2.getMapper(UserMapper.class);
            // 再次访问，因为现在使用的是一个新的SqlSession对象,所以会再次执行select语句
            User user2 = um.selectUserById(1);
            System.out.println(user2);
            // 关闭SqlSession对象
            sqlSession2.close();
        }
    
    }

**六 测试结果**

1 testCache1

DEBUG [main] ==>  Preparing: SELECT * FROM TB_USER WHERE id = ?
    DEBUG [main] ==> Parameters: 1(Integer)
    DEBUG [main] <==      Total: 1
    User [id=1, name=cakin, sex=男, age=18]
    User [id=1, name=cakin, sex=男, age=18]

2 testCache2

DEBUG [main] ==>  Preparing: SELECT * FROM TB_USER WHERE id = ?
    DEBUG [main] ==> Parameters: 1(Integer)
    DEBUG [main] <==      Total: 1
    User [id=1, name=cakin, sex=男, age=18]
    DEBUG [main] ==>  Preparing: DELETE FROM TB_USER WHERE id = ?
    DEBUG [main] ==> Parameters: 5(Integer)
    DEBUG [main] <==    Updates: 0
    DEBUG [main] ==>  Preparing: SELECT * FROM TB_USER WHERE id = ?
    DEBUG [main] ==> Parameters: 1(Integer)
    DEBUG [main] <==      Total: 1
    User [id=1, name=cakin, sex=男, age=18]

3 testCache3

DEBUG [main] ==>  Preparing: SELECT * FROM TB_USER WHERE id = ?
    DEBUG [main] ==> Parameters: 1(Integer)
    DEBUG [main] <==      Total: 1
    User [id=1, name=cakin, sex=男, age=18]
    DEBUG [main] ==>  Preparing: SELECT * FROM TB_USER WHERE id = ?
    DEBUG [main] ==> Parameters: 1(Integer)
    DEBUG [main] <==      Total: 1
    User [id=1, name=cakin, sex=男, age=18]

4 testCache4

DEBUG [main] ==>  Preparing: SELECT * FROM TB_USER WHERE id = ?
    DEBUG [main] ==> Parameters: 1(Integer)
    DEBUG [main] <==      Total: 1
    User [id=1, name=cakin, sex=男, age=18]
    DEBUG [main] ==>  Preparing: SELECT * FROM TB_USER WHERE id = ?
    DEBUG [main] ==> Parameters: 1(Integer)
    DEBUG [main] <==      Total: 1
    User [id=1, name=cakin, sex=男, age=18]