mybatis 第一个程序

思路：搭建环境 + 导入 Mybatis + 编写代码 + 测试

2.1 创建项目

• 导入依赖

  <!--导入依赖-->
  <dependencies>
      <!--mysql驱动-->
      <dependency>
          <groupId>mysql</groupId>
          <artifactId>mysql-connector-java</artifactId>
          <version>8.0.21</version>
      </dependency>
  
      <!--mybatis-->
      <dependency>
          <groupId>org.mybatis</groupId>
          <artifactId>mybatis</artifactId>
          <version>3.5.2</version>
      </dependency>
  
      <!--junit-->
      <dependency>
          <groupId>junit</groupId>
          <artifactId>junit</artifactId>
          <version>4.12</version>
      </dependency>
  </dependencies>
  

• 搭建数据库

create database mybatis;

use mybatis;

create table user(
	id int(20) not null primary key,
	name varchar(30) default null,
	pwd varchar(30) default null
);

insert into `user`(id, name, pwd) values
(1, '小费', '123456'),
(2, '小尤', '542103'),
(3, '小白', '888521')

2.2 创建一个模块

• 编写 mybatis 的核心配置文件

  <?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>
      <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="jdbc:mysql://localhost:3306/mybatis?useSSL=true&amp;useUnicode=true&amp;characterEncoding=utf8&amp;serverTimezone=GMT"/>
                  <property name="username" value="root"/>
                  <property name="password" value="123456"/>
              </dataSource>
          </environment>
      </environments>
  
      <mappers>
          <mapper resource="com/alivin/dao/UserMapper.xml"/>
      </mappers>
  </configuration>
  

• 编写 mybatis 工具类

  public class MybatisUtils {
  
      private static SqlSessionFactory sqlSessionFactory;
  
      static {
          try {
              // 1. 加载资源
              String resource = "mybatis-config.xml";
              // 2. 获取输入流
              InputStream inputStream = Resources.getResourceAsStream(resource);
              // 3. 使用 mybatis 获取 sqlSessionFactory 对象
              sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
          } catch (IOException e) {
              e.printStackTrace();
          }
      }
  
      // 有了 SqlSessionFactory，就可以从中获得 SqlSession 的实例
      // SqlSession 提供了在数据库执行 SQL 命令所需的所有方法
      public static SqlSession getSqlSession() {
          return sqlSessionFactory.openSession();
      }
  
  }
  
  

• 编写代码

  • 实体类

    public class User {
        private int id;
        private String name;
        private  String pwd;
    
        public User() {
        }
    
        public User(int id, String name, String pwd) {
            this.id = id;
            this.name = name;
            this.pwd = pwd;
        }
    
        public int getId() {
            return id;
        }
    
        public void setId(int id) {
            this.id = id;
        }
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public String getPwd() {
            return pwd;
        }
    
        public void setPwd(String pwd) {
            this.pwd = pwd;
        }
        
        @Override
        public String toString() {
            return "User{" +
                    "id=" + id +
                    ", uname='" + uname + '\'' +
                    ", pwd='" + pwd + '\'' +
                    '}';
        }
    }
    
    

  • Dao 接口

    public interface UserDao {
        List<User> getUserList();
    }
    

  • 接口实现类由原来的 UserDaoImpl 转变成一个 Mapper 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">
    <!--namespace=绑定了一个对应的 Dao/Mapper 接口-->
    <mapper namespace="com.alivin.dao.UserDao">
        <!--select 查询语句-->
        <select id="getUserList" resultType="com.alivin.pojo.User">
            select * from mybatis.user
        </select>
    </mapper>
    

2.4 测试

junit 测试

@Test
public void test() {
    // 获得 SqlSession 对象
    SqlSession sqlSession = MybatisUtils.getSqlSession();
    // 执行 SQL
    UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
    List<User> userList = userMapper.getUserList();

    for (User user : userList) {
        System.out.println(user);
    }

    sqlSession.close();
}