旧的设计方案

开发api的时候,需要先定义好接口的数据响应结果.如下是一个很简单直接的Controller实现方法及响应结果定义.

@RestController
@RequestMapping("/users")
public class UserController {

 @Inject
 private UserService userService;

 @GetRequest("/{userId:\\d+}")
 public ResponseBean signin(@PathVariable long userId) {
  try {
   User user = userService.getUserBaseInfo(userId);
   return ResponseBean.success(user);
  } catch (ServiceException e) {
   return new ReponseBean(e.getCode(), e.getMsg());
  } catch (Exception e) {
   return ResponseBean.systemError();
  }
 }
}

{
 code: "",
 data: {}, // 可以是对象或者数组
 msg: ""
}

从上面的代码，我们可以看到对于每个 Controller 方法，都会有很多重复的代码出现，我们应该设法去避免重复的代码。将重复的代码移除之后，可以得到如下的代码，简单易懂。

@RestController
@RequestMapping("/users")
public class UserController {
  
 @Inject
 private UserService userService;

 @GetRequest("/{userId:\\d+}")
 public User signin(@PathVariable long userId) {
  return userService.getUserBaseInfo(userId);
 }
}

在以上的实现中，还做了一个必要的要求，就是 ServiceException 需要定义为 RuntimeException的子类，而不是 Exception的子类。由于 ServiceException 表示服务异常，一般发生这种异常是应该直接提示前端，而无需进行其他特殊处理的。在定义为 RuntimeException 的子类之后，会减少大量的异常抛出声明，而且不再需要在事务@Transactional 中进行特殊声明。

统一 Controller 返回值格式

在开发的过程中，我发现上面的结构

@ControllerAdvice
public class ControllerResponseHandler implements ResponseBodyAdvice<Object> {
 
 private Logger logger = LogManager.getLogger(getClass());

 @Override
 public boolean supports(MethodParameter returnType, Class<? extends HttpMessageConverter<?>> converterType) {
  // 支持所有的返回值类型
  return true;
 }

 @Override
 public Object beforeBodyWrite(Object body, MethodParameter returnType, MediaType selectedContentType,
   Class<? extends HttpMessageConverter<?>> selectedConverterType, ServerHttpRequest request,
   ServerHttpResponse response) {
  if(body instanceof ResponseBean) {
   return body;
  } else {
   // 所有没有返回　ResponseBean　结构的结果均认为是成功的
   return ResponseBean.success(body);
  }
 }
}

统一异常处理

如下的代码中，ServiceException ServiceMessageException ValidatorErrorType FieldValidatorError 均为自定义类。

@ControllerAdvice
public class ControllerExceptionHandler {

 private Logger logger = LogManager.getLogger(getClass());

 private static final String logExceptionFormat = "[EXIGENCE] Some thing wrong with the system: %s";

 /**
  * 自定义异常
  */
 @ExceptionHandler(ServiceMessageException.class)
 public ResponseBean handleServiceMessageException(HttpServletRequest request, ServiceMessageException ex) {
  logger.debug(ex);
  return new ResponseBean(ex.getMsgCode(), ex.getMessage());
 }

 /**
  * 自定义异常
  */
 @ExceptionHandler(ServiceException.class)
 public ResponseBean handleServiceException(HttpServletRequest request, ServiceException ex) {
  logger.debug(ex);
  String message = codeToMessage(ex.getMsgCode());
  return new ResponseBean(ex.getMsgCode(), message);
 }

 /**
  * MethodArgumentNotValidException: 实体类属性校验不通过
  * 如: listUsersValid(@RequestBody @Valid UserFilterOption option)
  */
 @ExceptionHandler(MethodArgumentNotValidException.class)
 public ResponseBean handleMethodArgumentNotValid(HttpServletRequest request, MethodArgumentNotValidException ex) {
  logger.debug(ex);
  return validatorErrors(ex.getBindingResult());
 }

 private ResponseBean validatorErrors(BindingResult result) {
  List<FieldValidatorError> errors = new ArrayList<FieldValidatorError>();
  for (FieldError error : result.getFieldErrors()) {
   errors.add(toFieldValidatorError(error));
  }
  return ResponseBean.validatorError(errors);
 }

 /**
  * ConstraintViolationException: 直接对方法参数进行校验，校验不通过。
  * 如: pageUsers(@RequestParam @Min(1)int pageIndex, @RequestParam @Max(100)int pageSize)
  */
 @ExceptionHandler(ConstraintViolationException.class)
 public ResponseBean handleConstraintViolationException(HttpServletRequest request,
   ConstraintViolationException ex) {
  logger.debug(ex);
  // 
  List<FieldValidatorError> errors = new ArrayList<FieldValidatorError>();

  for (ConstraintViolation<?> violation : ex.getConstraintViolations()) {
   errors.add(toFieldValidatorError(violation));
  }
  return ResponseBean.validatorError(errors);
 }

 private FieldValidatorError toFieldValidatorError(ConstraintViolation<?> violation) {
  Path.Node lastNode = null;
  for (Path.Node node : violation.getPropertyPath()) {
   lastNode = node;
  }

  FieldValidatorError fieldNotValidError = new FieldValidatorError();
  // fieldNotValidError.setType(ValidatorTypeMapping.toType(violation.getConstraintDescriptor().getAnnotation().annotationType()));
  fieldNotValidError.setType(ValidatorErrorType.INVALID.value());
  fieldNotValidError.setField(lastNode.getName());
  fieldNotValidError.setMessage(violation.getMessage());
  return fieldNotValidError;
 }

 private FieldValidatorError toFieldValidatorError(FieldError error) {
  FieldValidatorError fieldNotValidError = new FieldValidatorError();
  fieldNotValidError.setType(ValidatorErrorType.INVALID.value());
  fieldNotValidError.setField(error.getField());
  fieldNotValidError.setMessage(error.getDefaultMessage());
  return fieldNotValidError;
 }

 /**
  * BindException: 数据绑定异常，效果与MethodArgumentNotValidException类似，为MethodArgumentNotValidException的父类
  */
 @ExceptionHandler(BindException.class)
 public ResponseBean handleBindException(HttpServletRequest request, BindException ex) {
  logger.debug(ex);
  return validatorErrors(ex.getBindingResult());
 }

 /**
  * 返回值类型转化错误
  */
 @ExceptionHandler(HttpMessageConversionException.class)
 public ResponseBean exceptionHandle(HttpServletRequest request,
   HttpMessageConversionException ex) {
  return internalServiceError(ex);
 }
 
 /**
  * 对应 Http 请求头的 accept
  * 客户器端希望接受的类型和服务器端返回类型不一致。
  * 这里虽然设置了拦截，但是并没有起到作用。需要通过http请求的流程来进一步确定原因。
  */
 @ExceptionHandler(HttpMediaTypeNotAcceptableException.class)
 public ResponseBean handleHttpMediaTypeNotAcceptableException(HttpServletRequest request,
   HttpMediaTypeNotAcceptableException ex) {
  logger.debug(ex);
  StringBuilder messageBuilder = new StringBuilder().append("The media type is not acceptable.")
    .append(" Acceptable media types are ");
  ex.getSupportedMediaTypes().forEach(t -> messageBuilder.append(t + ", "));
  String message = messageBuilder.substring(0, messageBuilder.length() - 2);

  return new ResponseBean(HttpStatus.NOT_ACCEPTABLE.value(), message);
 }

 /**
  * 对应请求头的 content-type
  * 客户端发送的数据类型和服务器端希望接收到的数据不一致
  */
 @ExceptionHandler(HttpMediaTypeNotSupportedException.class)
 public ResponseBean handleHttpMediaTypeNotSupportedException(HttpServletRequest request,
   HttpMediaTypeNotSupportedException ex) {
   logger.debug(ex);
  StringBuilder messageBuilder = new StringBuilder().append(ex.getContentType())
    .append(" media type is not supported.").append(" Supported media types are ");
  ex.getSupportedMediaTypes().forEach(t -> messageBuilder.append(t + ", "));
  String message = messageBuilder.substring(0, messageBuilder.length() - 2);
  System.out.println(message);
  return new ResponseBean(HttpStatus.UNSUPPORTED_MEDIA_TYPE.value(), message);
 }

 /**
  * 前端发送过来的数据无法被正常处理
  * 比如后天希望收到的是一个json的数据，但是前端发送过来的却是xml格式的数据或者是一个错误的json格式数据
  */
 @ExceptionHandler(HttpMessageNotReadableException.class)
 public ResponseBean handlerHttpMessageNotReadableException(HttpServletRequest request,
   HttpMessageNotReadableException ex) {
  logger.debug(ex);
  String message = "Problems parsing JSON";
  return new ResponseBean(HttpStatus.BAD_REQUEST.value(), message);
 }

 /**
  * 将返回的结果转化到响应的数据时候导致的问题。
  * 当使用json作为结果格式时，可能导致的原因为序列化错误。
  * 目前知道，如果返回一个没有属性的对象作为结果时，会导致该异常。
  */
 @ExceptionHandler(HttpMessageNotWritableException.class)
 public ResponseBean handlerHttpMessageNotWritableException(HttpServletRequest request,
   HttpMessageNotWritableException ex) {
  return internalServiceError(ex);
 }

 /**
  * 请求方法不支持
  */
 @ExceptionHandler(HttpRequestMethodNotSupportedException.class)
 public ResponseBean exceptionHandle(HttpServletRequest request, HttpRequestMethodNotSupportedException ex) {
  logger.debug(ex);
  StringBuilder messageBuilder = new StringBuilder().append(ex.getMethod())
    .append(" method is not supported for this request.").append(" Supported methods are ");

  ex.getSupportedHttpMethods().forEach(m -> messageBuilder.append(m + ","));
  String message = messageBuilder.substring(0, messageBuilder.length() - 2);
  return new ResponseBean(HttpStatus.METHOD_NOT_ALLOWED.value(), message);
 }

 /**
  * 参数类型不匹配
  */
 @ExceptionHandler(MethodArgumentTypeMismatchException.class)
 public ResponseBean methodArgumentTypeMismatchExceptionHandler(HttpServletRequest request,
   MethodArgumentTypeMismatchException ex) {
  logger.debug(ex);
  String message = "The parameter '" + ex.getName() + "' should of type '"
    + ex.getRequiredType().getSimpleName().toLowerCase() + "'";

  FieldValidatorError fieldNotValidError = new FieldValidatorError();
  fieldNotValidError.setType(ValidatorErrorType.TYPE_MISMATCH.value());
  fieldNotValidError.setField(ex.getName());
  fieldNotValidError.setMessage(message);

  return ResponseBean.validatorError(Arrays.asList(fieldNotValidError));
 }

 /**
  * 缺少必填字段
  */
 @ExceptionHandler(MissingServletRequestParameterException.class)
 public ResponseBean exceptionHandle(HttpServletRequest request,
   MissingServletRequestParameterException ex) {
  logger.debug(ex);
  String message = "Required parameter '" + ex.getParameterName() + "' is not present";

  FieldValidatorError fieldNotValidError = new FieldValidatorError();
  fieldNotValidError.setType(ValidatorErrorType.MISSING_FIELD.value());
  fieldNotValidError.setField(ex.getParameterName());
  fieldNotValidError.setMessage(message);

  return ResponseBean.validatorError(Arrays.asList(fieldNotValidError));
 }

 /**
  * 文件上传时，缺少　file 字段
  */
 @ExceptionHandler(MissingServletRequestPartException.class)
 public ResponseBean exceptionHandle(HttpServletRequest request, MissingServletRequestPartException ex) {
  logger.debug(ex);
  return new ResponseBean(HttpStatus.BAD_REQUEST.value(), ex.getMessage());
 }

 /**
  * 请求路径不存在
  */
 @ExceptionHandler(NoHandlerFoundException.class)
 public ResponseBean exceptionHandle(HttpServletRequest request, NoHandlerFoundException ex) {
  logger.debug(ex);
  String message = "No resource found for " + ex.getHttpMethod() + " " + ex.getRequestURL();
  return new ResponseBean(HttpStatus.NOT_FOUND.value(), message);
 }

 /**
  * 缺少路径参数
  * Controller方法中定义了　@PathVariable(required=true)　的参数，但是却没有在url中提供
  */
 @ExceptionHandler(MissingPathVariableException.class)
 public ResponseBean exceptionHandle(HttpServletRequest request, MissingPathVariableException ex) {
  return internalServiceError(ex);
 }

 /**
  * 其他所有的异常
  */
 @ExceptionHandler()
 public ResponseBean handleAll(HttpServletRequest request, Exception ex) {
  return internalServiceError(ex);
 }

 private String codeToMessage(int code) {
  //TODO 这个需要进行自定，每个 code 会匹配到一个相应的 msg
  return "The code is " + code;
 }

 private ResponseBean internalServiceError(Exception ex) {
  logException(ex);
  // do something else
  return ResponseBean.systemError();
 }

 private <T extends Throwable> void logException(T e) {
  logger.error(String.format(logExceptionFormat, e.getMessage()), e);
 }
}