Mybatis学习笔记 1

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POJO为数据库中的记录。

如何获得Mybatis的三种方式

• Maven仓库

  <!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
  <dependency>
      <groupId>org.mybatis</groupId>
      <artifactId>mybatis</artifactId>
      <version>3.5.9</version>
  </dependency>
  

• Github https://github.com/mybatis/mybatis-3

• 中文文档：https://mybatis.org/mybatis-3/zh/index.html

第一个Mybatis程序

• 搭建环境

• 新建一个Maven项目

  <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
  <dependency>
      <groupId>mysql</groupId>
      <artifactId>mysql-connector-java</artifactId>
      <version>5.1.46</version>
  </dependency>
  <!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
  <dependency>
      <groupId>org.mybatis</groupId>
      <artifactId>mybatis</artifactId>
      <version>3.5.9</version>
  </dependency>
  

• 编写核心配置文档

  <?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="${driver}"/>
          <property name="url" value="${url}"/>
          <property name="username" value="${username}"/>
          <property name="password" value="${password}"/>
        </dataSource>
      </environment>
    </environments>
    <mappers>
      <mapper resource="org/mybatis/example/BlogMapper.xml"/>
    </mappers>
  </configuration>
  

• 编写mybatis工具类

  public class MybatisUtil {
  	
  	private static SqlSessionFactory sqlSessionFactory = null;
  	
  	static {
  		InputStream inputStream;
  		try {
  			String resource = "mybatis-config.xml";
  			inputStream = Resources.getResourceAsStream(resource);
  			sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
  		} catch (IOException e) {
  			e.printStackTrace();
  		}
  	}
  	
  	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 int getId() {
  		return id;
  	}
  
  	public void setId(int id) {
  		this.id = id;
  	}
  	........
  }
  

• 编写对应的Dao接口

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

• 接口实现类由原来的UserDaoImpl转变为一个Mapper文件

  public class UserDaoImpl implements UserDao {
  
  	@Override
  	public List<User> getUserList() {
  		return null;
  	}
  }
  

  <?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="spring.helloMybatis.test01.UserDao">
    <select id="getUserList" resultType="spring.helloMybatis.test01.User">
      select * from mybatis.user where id = #{id}
    </select>
  </mapper>
  

• 测试

  public void test() {
  		
  	//第一步，获取sqlSession对象
  	SqlSession sqlSession = MybatisUtil.getSqlSession();
  		
  	//方式一：通过getMapper
  	UserDao userDao = sqlSession.getMapper(UserDao.class);
  	List<User> userList = userDao.getUserList();
  	for (User user :userList) {
  		System.out.println(user.toString());
  	}
  		
  	//方式二：通过命名空间
  	List<User> selectList = sqlSession.selectList("spring.helloMybatis.test01.UserDao.getUserList");
  	for (User user :selectList) {
  		System.out.println(user.toString());
  	}
  		
  	//关闭sqlSession
  	qlSession.close();
  }
  

• 特别注意点

  //namespace中的包名其实就是接口名
  <mapper namespace="spring.helloMybatis.test01.UserDao">
  
  //id其实就是接口中的方法名
  <select id="getUserList" resultType="spring.helloMybatis.test01.User">
      select * from mybatis.user where id = #{id}
  </select>