Mybatis介绍

<dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>3.5.7</version>
    </dependency>

2.在utils目录下目录下建立一个MybatisUtils类，通过这个工具类获得一个 sqlSession.

public class MybatisUtils {
    private static sqlSessionFactory sqlSessionFactory;

    static {
        try {
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsstream(resource);
            sqlSessionFactory = new sqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printstacktrace();
        }
    }
    //既然有了 sqlSessionFactory，顾名思义，我们可以从中获得 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();
    }
}

3.在resources目录下添加对 MyBatis 系统的核心设置的XML 配置文件mybatis-config.xml

<?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>

  <!--每写一个接口实现xml文件，都需要在这里配置相应的xml路径，现在先不写
  <mappers>
    <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
    <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
    <mapper resource="org/mybatis/builder/PostMapper.xml"/>
  </mappers>
  -->
</configuration>

4.在resources目录下添加一个db.properties文件，进行数据库的配置,

driver=org.postgresql.Driver
url=jdbc:postgresql://localhost:5432/postgres
username=username
password=123456

并在mybatis-config.xml中添加

5.在dao目录下建立对应的接口和实现类。不过使用了Mybatis后，用xml文件代替原来的实现类，这个文件头为

<?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指向的是dao接口文件的路径-->
<mapper namespace="org.mybatis.example.BlogMapper">
<!--id指向接口的方法名，resultType指向pojo包下的类名路径-->
  <select id="selectBlog" resultType="Blog">
    select * from Blog where id = #{id}
  </select>
</mapper>

6.测试函数

public void text() {
        //第一步获取sqlSession对象
        sqlSession sqlSession = MybatisUtils.getsqlSession();
        //方法一
        //第二步执行sql语句
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        List<User> userList = mapper.getUserList();
        //方法二
        //淘汰了//List<User> userList=sqlSession.selectList("com.huang.dao.UserDao.getUserList");
        for (User user : userList) {
            System.out.println(user);
        }
        //关闭资源
        sqlSession.close();
    }

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