public interface UserDao {
 //根据id查询用户信息
 public User findUserById(int id) throws Exception;
 //添加用户信息
 public void insertUser(User user) throws Exception;
 //删除用户信息
 public void deleteUser(int id) throws Exception;
}

public class UserDaoImpl implements UserDao{
 //需要向dao实现类中注入SqlSessionFactory
 //这里通过构造方法注入
 private SqlSessionFactory sqlSessionFactory;
 public UserDaoImpl(SqlSessionFactory sqlSessionFactory) {
  super();
  this.sqlSessionFactory = sqlSessionFactory;
 }
 @Override
 public User findUserById(int id) throws Exception {
  SqlSession sqlSession=sqlSessionFactory.openSession();
  User user=sqlSession.selectOne("test.findUserById", id);
  //释放资源
  sqlSession.close();
  return user;
 }
 @Override
 public void insertUser(User user) throws Exception {
  SqlSession sqlSession=sqlSessionFactory.openSession();
  sqlSession.insert("test.insertUser", user);
  //提交事务
  sqlSession.commit();
  //释放资源
  sqlSession.close();
 }
 @Override
 public void deleteUser(int id) throws Exception {
  SqlSession sqlSession=sqlSessionFactory.openSession();
  sqlSession.delete("test.deleteUser", id);
  //提交事务
  sqlSession.commit();
  //释放资源
  sqlSession.close();
 }
}

public class UserDaoImplTest {
 private SqlSessionFactory sqlSessionFactory;
 @Before
 public void setUp() throws IOException{
  //创建sqlSessionFactory
  //mybatis配置文件
  String resource="SqlMapConfig.xml";
  //得到配置文件流
  InputStream inputStream=Resources.getResourceAsStream(resource);
  //创建会话工厂，传入mybatis的配置文件信息
  sqlSessionFactory=new SqlSessionFactoryBuilder().build(inputStream);
 }
 @Test
 public void findUserByIdTest() throws Exception{
  UserDao userDao=new UserDaoImpl(sqlSessionFactory);
  User user=userDao.findUserById(1);
  System.out.println(user);
 }
}

User user = sqlSession.selectOne("test.findUserById", id);
sqlSession.insert("test.insertUser", user);
......

package joanna.yan.mybatis.mapper;
import java.util.List;
import joanna.yan.mybatis.entity.User;
/**
 * 相当于dao接口
 * @author Joanna.Yan
 *
 */
public interface UserMapper {
 //根据id查询用户信息
 public User findUserById(int id) throws Exception;
 //根据名字查询用户
 public List<User> findUserByName(String name) throws Exception;
 //添加用户信息
 public void insertUser(User user) throws Exception;
 //删除用户信息
 public void deleteUser(int id) throws Exception;
}

<?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命名空间，作用就是对sql进行分类化的管理，理解为sql隔离
 注意：使用mapper代理开发时，namespace有特殊作用，namespace等于mapper接口地址 -->
<mapper namespace="joanna.yan.mybatis.mapper.UserMapper">
 <select id="findUserById" parameterType="java.lang.Integer" resultType="joanna.yan.mybatis.entity.User">
  select * from user where id=#{id}
 </select>
 <select id="findUserByName" parameterType="java.lang.String" resultType="joanna.yan.mybatis.entity.User">
  select * from user where username LIKE '%${value}%'
 </select>
</mapper>

public class UserMapperTest {
private SqlSessionFactory sqlSessionFactory;
 @Before
 public void setUp() throws IOException{
  //创建sqlSessionFactory
  //mybatis配置文件
  String resource="SqlMapConfig.xml";
  //得到配置文件流
  InputStream inputStream=Resources.getResourceAsStream(resource);
  //创建会话工厂，传入mybatis的配置文件信息
  sqlSessionFactory=new SqlSessionFactoryBuilder().build(inputStream);
 }
 @Test
 public void findUserByIdTest() throws Exception{
  SqlSession sqlSession=sqlSessionFactory.openSession();
  //创建UserMapper对象，mybatis自动生成mapper代理对象
  UserMapper userMapper=sqlSession.getMapper(UserMapper.class);
  //调用userMapper的方法
  User user=userMapper.findUserById(1);
  System.out.println(user);
 }
 @Test
 public void findUserByNameTest() throws Exception{
  SqlSession sqlSession=sqlSessionFactory.openSession();
  //创建UserMapper对象，mybatis自动生成mapper代理对象
  UserMapper userMapper=sqlSession.getMapper(UserMapper.class);
  //调用userMapper的方法
  List<User> list=userMapper.findUserByName("小明");
  System.out.println(list);
 }
}