MyBatis框架：第五章：源码解析及Mapper接口方式的mybatis的增，删，改，查实现

public interface UserMapper {    
    // 保存用户
    public int saveUser(User user);    
    // 更新用户
    public int updateUser(User user);    
    // 根据id删除用户
    public int deleteUserById(int id);    
    // 根据id搜索用户
    public User findUserById(int id);    
    // 搜索全部用户
    public List<User> findUsers();
}

<?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.dao.UserMapper">
<!--  public Integer saveUser(User user); -->
  <insert id="saveUser" parameterType="com.pojo.User">
    insert into t_user(`last_name`,`sex`) values(#{lastName},#{sex})
  </insert>
<!--  public Integer updateUser(User user); -->
  <update id="updateUser" parameterType="com.pojo.User">
    update t_user set last_name = #{lastName} , sex = #{sex} where id = #{id}
  </update>
<!--  public Integer deleteUserById(Integer id); -->
  <delete id="deleteUserById">
    delete from t_user where id = #{id}
  </delete> 
<!--  public User findUserById(Integer id); -->
  <select id="findUserById" resultType="com.pojo.User">
    select id,last_name lastName,sex from t_user where id = #{id}
  </select>
<!--  public List<User> findUsers(); -->
  <select id="findUsers" resultType="com.pojo.User">
    select id,last_name lastName,sex from t_user
  </select>
</mapper>

public class UserMapperTest {
  static SqlSessionFactory sqlSessionFactory;
  @BeforeClass
  public static void setUpBeforeClass() throws Exception {
    String url = "mybatis-config.xml";
    // 读取配置文件
    InputStream inputStream = Resources.getResourceAsStream(url);
    // 创建SqlSessionFactory对象
    sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
  }
  @Test
  public void testSaveUser() {
    SqlSession session = sqlSessionFactory.openSession();
    try {
      UserMapper userMapper = session.getMapper(UserMapper.class);
      User user = new User(0, "ddddd", 1);
      userMapper.saveUser(user);
      session.commit();
      System.out.println(user);
    } finally {
      session.close();
    }
  }
  @Test
  public void testUpdateUser() {
    SqlSession session = sqlSessionFactory.openSession();
    try {
      UserMapper userMapper = session.getMapper(UserMapper.class);
      User user = new User(4, "eeeee", 1);
      userMapper.updateUser(user);
      session.commit();
    } finally {
      session.close();
    }
  }
  @Test
  public void testDeleteUserById() {
    SqlSession session = sqlSessionFactory.openSession();
    try {
      UserMapper userMapper = session.getMapper(UserMapper.class);
      userMapper.deleteUserById(4);
      session.commit();
    } finally {
      session.close();
    }
  }
  @Test
  public void testFindUserById() {
    SqlSession session = sqlSessionFactory.openSession();
    try {
      UserMapper userMapper = session.getMapper(UserMapper.class);
      System.out.println(userMapper.findUserById(1));
    } finally {
      session.close();
    }
  }
  @Test
  public void testFindUsers() {
    SqlSession session = sqlSessionFactory.openSession();
    try {
      UserMapper userMapper = session.getMapper(UserMapper.class);
      System.out.println(userMapper.findUsers());
    } finally {
      session.close();
    }
  }
}

public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
    return mapperRegistry.getMapper(type, sqlSession);
  }

@SuppressWarnings("unchecked")
  public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
    final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type);
    if (mapperProxyFactory == null) {
      throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
    }
    try {
      return mapperProxyFactory.newInstance(sqlSession);
    } catch (Exception e) {
      throw new BindingException("Error getting mapper instance. Cause: " + e, e);
    }
  }

@SuppressWarnings("unchecked")
  protected T newInstance(MapperProxy<T> mapperProxy) {
    return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
  }

   case SELECT:
            if (method.returnsVoid() && method.hasResultHandler()) {
              executeWithResultHandler(sqlSession, args);
              result = null;
            } else if (method.returnsMany()) {
              result = executeForMany(sqlSession, args);
            } else if (method.returnsMap()) {
              result = executeForMap(sqlSession, args);
            } else if (method.returnsCursor()) {
              result = executeForCursor(sqlSession, args);
            } else {
              Object param = method.convertArgsToSqlCommandParam(args);
              result = sqlSession.selectOne(command.getName(), param);
            }
            break;

  // 根据id搜索用户
  public User findUserById(int id);    
  // 搜索全部用户
  public List<User> findUsers();

public MethodSignature(Configuration configuration, Class<?> mapperInterface, Method method) {
  Type resolvedReturnType = TypeParameterResolver.resolveReturnType(method, mapperInterface);
  if (resolvedReturnType instanceof Class<?>) {
    this.returnType = (Class<?>) resolvedReturnType;
  } else if (resolvedReturnType instanceof ParameterizedType) {
    this.returnType = (Class<?>) ((ParameterizedType) resolvedReturnType).getRawType();
  } else {
    this.returnType = method.getReturnType();
  }
  this.returnsVoid = void.class.equals(this.returnType);
  this.returnsMany = (configuration.getObjectFactory().isCollection(this.returnType) || this.returnType.isArray());

if (method.hasRowBounds()) {
          RowBounds rowBounds = method.extractRowBounds(args);
          result = sqlSession.<E>selectList(command.getName(), param, rowBounds);
        } else {
          result = sqlSession.<E>selectList(command.getName(), param);
        }