初学mybatis

区别:

　　com.mysql.jdbc.Driver 是 mysql-connector-java 5中的

　　com.mysql.cj.jdbc.Driver 是 mysql-connector-java 6以上的版本中的

第一步导入相应的依赖 

<dependencies>
    <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>8.0.20</version>
    </dependency>
    <!-- https://mvnrepository.com/artifact/junit/junit -->
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.12</version>
    </dependency>
    <!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>3.5.2</version>
    </dependency>
</dependencies>

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

注意点 mapper对应的resource以/为分割

编写工具类为获得sqlsession的实例

public class MybatisUtil {
    private static SqlSessionFactory sqlSessionFactory;
    //加载资源
    static {
        try {
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    //创建工具类获取sqlsession对象
    public static SqlSession getSqlSession(){
        return sqlSessionFactory.openSession();
    }
}

 

接下来编写接口类 以UserMapper为例

public interface UserMapper {
    List<User> getUser();
}

添加xml绑定此接口

<?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="com.Reader.Dao.UserMapper">
    <select id="getUser" resultType="com.Reader.pojo.User">
        select * from mybatis.user;
    </select>
</mapper>

注意点 namespace与resultType为全路径

 当使用

        <package name="com.Reader.pojo"/>

可使用注解

@Alias("hello")进行单个类的命名修改