MyBatis入门篇

持久层解决方案

JDBC技术：Connection; PreparedStatement; ResultSet
Spring的JdbcTemplate: Spring中对jdbc的简单封装
Apache的DBUtils:它和Spring的JdbcTemplate很想，也是对Jdbc的简单封装

但是，以上都不是框架，JDBC是规范，Spring的JdbcTemplate和Apache的DBUtils都只是工具类

MyBatis框架概述

mybatis是一款优秀的基于java的持久层框架。采用ORM思想解决实体和数据映射的问题，对jdbc进行了封装，屏蔽了jdbc api底层访问细节，使得开发人员不用于jdbc api打交道，就可以完成对数据库的持久化操作。ORM: Object Relational Mapping 对象关系映射简单的说，就是把数据库表和实体类以及实体类的属性对应起来，让我们可以操作实体类就实现操作数据库表。mybatis官方文档：https://mybatis.org/mybatis-3/zh/index.html

入门案例

需要的maven依赖

<dependencies>
  <dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis</artifactId>
    <version>3.5.4</version>
  </dependency>
  <dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.19</version>
  </dependency>
  <dependency>
    <groupId>log4j</groupId>
    <artifactId>log4j</artifactId>
    <version>1.2.17</version>
  </dependency>
  <dependency>
    <groupId>junit</groupId>
    <artifactId>junit</artifactId>
    <version>4.12</version>
  </dependency>
</dependencies>

在导入mybatis依赖之后，只需要通过配置文件和实体类文件就可以

<!--mybatis config文件-->
<?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>
    <!--配置环境-->
    <environments default="mysql">
        <!--mysql环境-->
        <environment id="mysql">
            <!--事务-->
            <transactionManager type="JDBC"/>
            <!--数据源-->
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://127.0.0.1:3306/mybatis-learn?serverTimezone=UTC"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
    <!--配置mapper-->
    <mappers>
        <mapper resource="mapper/UserMapper.xml"/>
    </mappers>
</configuration>

//实体类，对应数据库中的表
public class User {
    private Long userId;
    private String userName;
    private Long sex;
    private String address;
    private String email;
    private String phone;
    private String password;

    public Long getUserId() {
        return userId;
    }

    public void setUserId(Long userId) {
        this.userId = userId;
    }

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public Long getSex() {
        return sex;
    }

    public void setSex(Long sex) {
        this.sex = sex;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getPhone() {
        return phone;
    }

    public void setPhone(String phone) {
        this.phone = phone;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    @Override
    public String toString() {
        return "User{" +
                "userId=" + userId +
                ", userName='" + userName + '\'' +
                ", sex=" + sex +
                ", address='" + address + '\'' +
                ", email='" + email + '\'' +
                ", phone='" + phone + '\'' +
                ", password='" + password + '\'' +
                '}';
    }
}

// UserMapper 接口
public interface UserMapper {
    List<User> selectAll();
    @Select("select * from user")
    List<User> findAll();
}

// 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="infra.mapper.UserMapper">
    <!-- 根据命名空间+方法名确定对应Mapper的全限定类名   -->
    <select id="selectAll" resultType="domain.entity.User">
        select * from user
    </select>
</mapper>

// 测试类
public class TestUser {
    @Test
    public void test1(){
        InputStream inputStream = null;
        SqlSession session = null;
        try {
            // 1. 读取配置文件
            String resource = "mybatis-config.xml";
            inputStream = Resources.getResourceAsStream(resource);
            // 2. 创建SqlSessionFactory对象
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
            // 3. 使用sqlSessionFactory生产SqlSession对象
            session = sqlSessionFactory.openSession();
            // 4. 使用SqlSession创建Mapper的动态代理对象
            UserMapper mapper = session.getMapper(UserMapper.class);
            // 5. 使用代理对象执行方法
            List<User> users = mapper.selectAll();
            System.out.println(users.toString());
            List<User> all = mapper.findAll();
            System.out.println(all.toString());
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            // 6. 释放资源
            if(null != inputStream){
                try {
                    inputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if(null != session){
                session.close();
            }
        }
    }
}

通过上面简单的案例可以达到初步使用mybatis的目的。

持久层解决方案#

MyBatis框架概述#

入门案例#

持久层解决方案

MyBatis框架概述

入门案例