【mybatis基础(一)】mybatis入门案例

什么是 MyBatis？

        MyBatis 是一款优秀的持久层框架，它支持自定义 SQL、存储过程以及高级映射。MyBatis 免除了几乎所有的 JDBC 代码以及设置参数和获取结果集的工作。MyBatis 可以通过简单的 XML 或注解来配置和映射原始类型、接口和 Java POJO（Plain Old Java Objects，普通老式 Java 对象）为数据库中的记录。mybatis – MyBatis 3 | 简介

一、入门案例

1、依赖准备

    <dependencies>
        <dependency>
            <groupId>org.mybatisgroupId>
            <artifactId>mybatisartifactId>
            <version>3.5.5version>
        dependency>
        <dependency>
            <groupId>mysqlgroupId>
            <artifactId>mysql-connector-javaartifactId>
            <version>8.0.11version>
        dependency>
        <dependency>
            <groupId>junitgroupId>
            <artifactId>junitartifactId>
            <version>4.12version>
            <scope>testscope>
        dependency>
        <dependency>
            <groupId>log4jgroupId>
            <artifactId>log4jartifactId>
            <version>1.2.12version>
        dependency>
    dependencies>

2、数据库准备

DROP TABLE IF EXISTS `tb_users`;
CREATE TABLE `tb_users`  (
  `id` int(20) NOT NULL COMMENT '编号主键',
  `username` varchar(50) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NOT NULL COMMENT '用户名',
  `birthday` date NOT NULL COMMENT '出生日期',
  `sex` varchar(2) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NOT NULL COMMENT '性别',
  `address` varchar(100) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NOT NULL COMMENT '地址',
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8mb4 COLLATE = utf8mb4_0900_ai_ci ROW_FORMAT = Dynamic;
 

 3、编写Entity层

public class User implements Serializable {
 
    private Integer id;
    private String username;
    private Date birthday;
    private String sex;
    private String address;
 
    /*
        提供set、get方法
    */
 
    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", birthday=" + birthday +
                ", sex='" + sex + '\'' +
                ", address='" + address + '\'' +
                '}';
    }
}

 4、编写Dao层

public interface UserDao {
    List findAll();
}

 5、Dao层的Mapper映射文件

写法一、使用配置文件编写sql

mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.qiu.dao.UserDao">
    
    <select id="findAll" resultType="com.qiu.model.User">
        select *
        from tb_users;
    select>
mapper>

 6、DataSource 配置文件（dao层对应mapper.xml文件）

configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <environments default="mysql">
        <environment id="mysql">
            
            <transactionManager type="JDBC">transactionManager>
            
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/test2?
                        serverTimezone=UTC&useUnicode=true&characterEncoding=utf8"/>
                <property name="username" value="${username}"/>
                <property name="password" value="${password}"/>
            dataSource>
        environment>
    environments>
    
    <mappers>
        <mapper resource="mapper/UserMapper.xml"/>
    mappers>
configuration>

 注意mapper标签用法

<mappers>
  <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
mappers>
<mappers>
  <mapper url="file:///var/mappers/AuthorMapper.xml"/>
mappers>
<mappers>
  <mapper class="org.mybatis.builder.AuthorMapper"/>
mappers>

7、编写测试类

public class MybatisTest {
    public static void main(String[] args) throws IOException {
        //1、读取配置文件
        InputStream in = Resources.getResourceAsStream("config/SqlMapConfig.xml");
        //2.创建 SqlSessionFactory 的构建者对象
        SqlSessionFactoryBuilder builder=new SqlSessionFactoryBuilder();
        //3.使用构建者创建工厂对象 SqlSessionFactory
        SqlSessionFactory sessionFactory = builder.build(in);
        //4.使用 SqlSessionFactory 生产 SqlSession 对象
        SqlSession sqlSession = sessionFactory.openSession();
        //5.使用 SqlSession 创建 dao 接口的代理对象
        UserDao userMapper = sqlSession.getMapper(UserDao.class);
        //6.使用代理对象执行查询所有方法 List
        List users = userMapper.findAll();
        for (User user : users) {
            System.out.println(user);
        }
        //7.释放资源
        sqlSession.close();
        in.close();
    }
}

 【显示结果】

 写法二、使用注解编写sql

public interface UserDao {
    @Select("select * from tb_users")
    List findAll();
}

更改mapperbb标签，其他不变 

 OKk!!! 入门mybatis