初次体验MyBatis的注意事项

<?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.jdbc.Driver" />
            <property name="url" value="jdbc:mysql://localhost:3306/mybatis" />
            <property name="username" value="root" />
            <property name="password" value="123456" />
         </dataSource>
      </environment>
   </environments>
   <!-- 将我们写好的sql映射文件（EmployeeMapper.xml）一定要注册到全局配置文件（mybatis-config.xml）中 -->
   <mappers>
      <mapper resource="EmployeeMapper.xml" />
   </mappers>
</configuration>

<?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.atguigu.mybatis.dao.EmployeeMapper">
<!-- 
namespace:名称空间;指定为接口的全类名
id：唯一标识
resultType：返回值类型
#{id}：从传递过来的参数中取出id值

public Employee getEmpById(Integer id);
分离实现与接口
 -->
   <select id="getEmpById" resultType="com.atguigu.mybatis.bean.Employee">
      select id,last_name lastName,email,gender from tbl_employee where id = #{id}
   </select>
</mapper>

<mappers>
   <mapper resource="EmployeeMapper.xml" />
</mappers>

String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

SqlSession openSession = sqlSessionFactory.openSession();

try {
   Employee employee = openSession.selectOne(
         "com.atguigu.mybatis.dao.EmployeeMapper.getEmpById", 1); // spacename + sqlId
   System.out.println(employee);
} finally {
   openSession.close();
}

mybatis：    Mapper.java(接口) ====>  xxMapper.xml(实现)