Mybatis学习笔记10 高级映射及延迟加载

Mybatis学习笔记9 动态SQL_biubiubiu0706的博客-CSDN博客

无论简单映射(前面所学的单表和对象之间的映射关系)还是高级映射

说到底都是java对象和数据库表记录之间的映射关系

准备数据库表:一个班级对应多个学生.班级表:t_class 学生表:s_stu(自增)

新建模块

项目整体结构

pom.xml


<?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">
    <modelVersion>4.0.0</modelVersion>
 
    <groupId>org.example</groupId>
    <artifactId>mybatis-09</artifactId>
    <version>1.0-SNAPSHOT</version>
 
    <properties>
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
    </properties>
 
    <dependencies>
        <!--mybatis依赖-->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.10</version>
        </dependency>
        <!--mysql依赖-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.30</version>
        </dependency>
        <!--logback依赖-->
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-classic</artifactId>
            <version>1.2.11</version>
        </dependency>
        <!--junit依赖-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13.2</version>
            <scope>test</scope>
        </dependency>
    </dependencies>
</project>

SqlSessionUtil


package example.utils;
 
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;
 
/**
 * @author hrui
 * @date 2023/9/8 14:55
 */
public class SqlSessionUtil {
 
    //工具类的构造方法一般都是私有化
    //方法都是静态的
    //为了防止new对象,构造方法私有化
    private SqlSessionUtil(){
 
    }
    private static SqlSessionFactory sqlSessionFactory;
 
    //类加载时候执行
    //SqlSessionUtil工具类在被加载的时候,解析mybatis-config1.xml.创建sqlSessionFactory对象
    static{
        try {
            //SqlSessionFactoryBuilder sqlSessionFactoryBuilder=new SqlSessionFactoryBuilder();
            //下面这么写的原因是SqlSessionFactoryBuilder就是为了创建sqlSessionFactory而来的,使用完后,就不需要,都不需要创建个局部变量
            //一个sqlSessionFactory对应一个数据库
            sqlSessionFactory= new SqlSessionFactoryBuilder().build(Resources.getResourceAsStream("mybatis-config1.xml"));
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
 
    //全局的 服务器级别的,一个服务器当中定义一个即可
    private static ThreadLocal<SqlSession> local=new ThreadLocal<>();
 
    //获取会话对象 返回会话对象
    public static SqlSession openSession(){
        SqlSession sqlSession=local.get();
        if(sqlSession==null){
            sqlSession = sqlSessionFactory.openSession();
            local.set(sqlSession);
        }
 
        return sqlSession;
    }
 
    //提供一个关闭的方法
    public static void close(SqlSession sqlSession){
        if(sqlSession!=null){
            //因为核心配置文件中配置POOLED  这里关闭是交还给连接池
            sqlSession.close();
            //注意移除SqlSession对象和当前线程的绑定关系
            //因为Tomcat服务器支持线程池 比如说t1线程用完了,close交还给连接池了,这个sqlSession属于不可用的状态,你没有remove出去 如果t2线程拿到了,那么这个sqlSession不可用
            local.remove();
        }
    }
}

logback.xml


<?xml version="1.0" encoding="UTF-8"?>
<configuration debug="false">
    <!--定义⽇志⽂件的存储地址-->
    <property name="LOG_HOME" value="D:/home"/>
    <!-- 控制台输出 -->
    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
        <encoder class="ch.qos.logback.classic.encoder.PatternLayoutEncoder">
            <!--格式化输出：%d表示⽇期，%thread表示线程名，%-5level：级别从左显示5
           个字符宽度%msg：⽇志消息，%n是换⾏符-->
            <pattern>%d{yyyy-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{50} - %msg%n</pattern>
        </encoder>
    </appender>
    <!-- 按照每天⽣成⽇志⽂件 -->
    <appender name="FILE" class="ch.qos.logback.core.rolling.RollingFileAppender">
        <rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">
            <!--⽇志⽂件输出的⽂件名-->
            <FileNamePattern>${LOG_HOME}/TestWeb.log.%d{yyyy-MM-dd}.log</FileNamePattern>
            <!--⽇志⽂件保留天数-->
            <MaxHistory>30</MaxHistory>
        </rollingPolicy>
        <encoder class="ch.qos.logback.classic.encoder.PatternLayoutEncoder">
            <!--格式化输出：%d表示⽇期，%thread表示线程名，%-5level：级别从左显示5
           个字符宽度%msg：⽇志消息，%n是换⾏符-->
            <pattern>%d{yyyy-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logge
                r{50} - %msg%n</pattern>
        </encoder>
        <!--⽇志⽂件最⼤的⼤⼩-->
        <triggeringPolicy class="ch.qos.logback.core.rolling.SizeBasedTriggeringPolicy">
            <MaxFileSize>100MB</MaxFileSize>
        </triggeringPolicy>
    </appender>
    <!--mybatis log configure-->
    <logger name="com.apache.ibatis" level="TRACE"/>
    <logger name="java.sql.Connection" level="DEBUG"/>
    <logger name="java.sql.Statement" level="DEBUG"/>
    <logger name="java.sql.PreparedStatement" level="DEBUG"/>
    <!-- ⽇志输出级别,logback⽇志级别包括五个：TRACE < DEBUG < INFO < WARN < ERROR -->
    <root level="DEBUG">
        <appender-ref ref="STDOUT"/>
        <appender-ref ref="FILE"/>
    </root>
</configuration>

核心配置文件


"1.0" encoding="UTF-8" ?>
configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <settings>
        
        <setting name="mapUnderscoreToCamelCase" value="true"/>
    settings>
 
    
    <typeAliases>
        <package name="example.pojo"/>
        
    typeAliases>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="1"/>
                <property name="username" value="1"/>
                <property name="password" value="1!"/>
                <property name="poolMaximumActiveConnections" value="10"/>
 
                <property name="poolMaximumIdleConnections" value="5"/>
                <property name="poolMaximumCheckoutTime" value="20000"/>
            dataSource>
        environment>
    environments>
    
    
    
    <mappers>
        <mapper resource="mapper/StuMapper.xml"/>
        <mapper resource="mapper/ClazzMapper.xml"/>
    mappers>
configuration>