mybatis（Mybatis与hibernate的不同、原始Dao开发、Mapper动态代理开发）

1、Mybatis与hibernate的不同

（1）Mybatis和hibernate不同，它不完全是一个ORM框架，因为MyBatis需要程序员自己编写Sql语句。mybatis可以通过XML或注解方式灵活配置要运行的sql语句，并将java对象和sql语句映射生成最终执行的sql，最后将sql执行的结果再映射生成java对象。

 mybatis需要在配置文件中书写sql语句：

    <delete id="deleteStudentById" parameterType="Integer">
        delete from student
        where studentno = #{value}
    </delete>

（2）Mybatis学习门槛低，简单易学，程序员直接编写原生态sql，可严格控制sql执行性能，灵活度高，非常适合对关系数据模型要求不高的软件开发，例如互联网软件、企业运营类软件等，因为这类软件需求变化频繁，一但需求变化要求成果输出迅速。但是灵活的前提是mybatis无法做到数据库无关性，如果需要实现支持多种数据库的软件则需要自定义多套sql映射文件，工作量大。

（3）Hibernate对象/关系映射能力强，数据库无关性好，对于关系模型要求高的软件（例如需求固定的定制化软件）如果用hibernate开发可以节省很多代码，提高效率。但是Hibernate的学习门槛高，要精通门槛更高，而且怎么设计O/R映射，在性能和对象模型之间如何权衡，以及怎样用好Hibernate需要具有很强的经验和能力才行。总之，按照用户的需求在有限的资源环境下只要能做出维护性、扩展性良好的软件架构都是好架构，所以框架只有适合才是最好。 

2、原始Dao开发

（1）创建接口：

public interface StudentDao {
    public Student selectStudentById(Integer id);
}

（2）创建接口的实现类：

public class StudentDaoImp implements StudentDao{
    private SqlSessionFactory sqlSessionFactory;

    public StudentDaoImp(SqlSessionFactory sqlSessionFactory) {
        this.sqlSessionFactory = sqlSessionFactory;
    }

    public Student selectStudentById(Integer studentno){
        SqlSession sqlSession = sqlSessionFactory.openSession();
        return sqlSession.selectOne("test.findStudentById", studentno);
    }
}

（3）创建测试类：

public class Test1 {
    public SqlSessionFactory sqlSessionFactory;

    public void before() throws Exception {
        String resource = "sqlMapConfig.xml";
        InputStream in = Resources.getResourceAsStream(resource);
        sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
    }

    public void testDao() throws Exception {
        StudentDao studentDao = new StudentDaoImp(sqlSessionFactory);
        Student student=studentDao.selectStudentById(201811);
        System.out.println(student);
    }

    public static void main(String args []){
        Test1 test1=new Test1();
        try {
            test1.before();
            test1.testDao();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

DEBUG [main] - Logging initialized using 'class org.apache.ibatis.logging.slf4j.Slf4jImpl' adapter.
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - Opening JDBC Connection
DEBUG [main] - Created connection 1750905143.
DEBUG [main] - Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@685cb137]
DEBUG [main] - ==>  Preparing: select * from student where studentno = ? 
DEBUG [main] - ==> Parameters: 201811(Integer)
DEBUG [main] - <==      Total: 1
Student [studentno=201811, sname=zhai, sex=男, birthday=1998-11-11, classno=tx171, point=890, phone=1234567890, email=null]

3、mapper动态代理开发

（1）接口：

public interface StudentMapper {
     Student findStudentById(Integer studentno);
}

• Mapper接口方法名和xml中定义的每个statement的id相同
• Mapper接口方法的输入参数类型和mapper.xml中定义的每个sql 的parameterType的类型相同
• Mapper接口方法的输出参数类型和mapper.xml中定义的每个sql的resultType的类型相同

（2）配置文件（注意命名空间）：

<mapper namespace="pers.zhb.mapper.StudentMapper">
    <select id="findStudentById" parameterType="Integer" resultType="pers.zhb.pojo.Student">
        select * from student where studentno = #{v}
    </select>

注意：xml文件中的namespace与mapper接口的类路径相同

（3）测试：

public class StudentMapperTest {
    public void testMapper() throws Exception {
        //加载核心配置文件
        String resource = "sqlMapConfig.xml";
        InputStream in = Resources.getResourceAsStream(resource);
        //创建SqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
        //创建SqlSession
        SqlSession sqlSession = sqlSessionFactory.openSession();
        //SqlSEssion帮我生成一个实现类  （给接口）
        StudentMapper studentMapper = sqlSession.getMapper(StudentMapper.class);

        Student student = studentMapper.findStudentById(201811);
        System.out.println(student);
    }

DEBUG [main] - Logging initialized using 'class org.apache.ibatis.logging.slf4j.Slf4jImpl' adapter.
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - Opening JDBC Connection
DEBUG [main] - Created connection 1291286504.
DEBUG [main] - Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@4cf777e8]
DEBUG [main] - ==>  Preparing: select * from student where studentno = ? 
DEBUG [main] - ==> Parameters: 201811(Integer)
DEBUG [main] - <==      Total: 1
Student [studentno=201811, sname=zhai, sex=男, birthday=1998-11-11, classno=tx171, point=890, phone=1234567890, email=null]