[译]REST API 的自定义错误消息处理

2023-08-25

1. 概述

在本教程中，我们将讨论如何为 Spring REST API 实现全局错误处理程序。

我们将使用每个异常的语义为客户端构建有意义的错误消息，其明确的目标是为客户端提供所有信息以轻松诊断问题。

2. 自定义错误消息

让我们首先实现一个用于通过线路发送错误的简单结构 — ApiError：

public class ApiError {

    private HttpStatus status;
    private String message;
    private List<String> errors;

    public ApiError(HttpStatus status, String message, List<String> errors) {
        super();
        this.status = status;
        this.message = message;
        this.errors = errors;
    }

    public ApiError(HttpStatus status, String message, String error) {
        super();
        this.status = status;
        this.message = message;
        errors = Arrays.asList(error);
    }
}

这里的信息应该很简单：

status – HTTP 状态代码
message – 与异常相关的错误消息
error – 构建的错误消息列表

当然，对于 Spring 中的实际异常处理逻辑，我们将使用 @ControllerAdvice 注解：

@ControllerAdvice
public class CustomRestExceptionHandler extends ResponseEntityExceptionHandler {
    ...
}

3. 处理错误请求异常

3.1.处理异常

现在让我们看看如何处理最常见的客户端错误 - 基本上是客户端向 API 发送无效请求的情况：

BindException – 发生致命绑定错误时抛出此异常。
MethodArgumentNotValidException – 当使用 @Valid 注解的参数验证失败时抛出此异常：

@Override
protected ResponseEntity<Object> handleMethodArgumentNotValid(
  MethodArgumentNotValidException ex,
  HttpHeaders headers,
  HttpStatus status,
  WebRequest request) {
    List<String> errors = new ArrayList<String>();
    for (FieldError error : ex.getBindingResult().getFieldErrors()) {
        errors.add(error.getField() + ": " + error.getDefaultMessage());
    }
    for (ObjectError error : ex.getBindingResult().getGlobalErrors()) {
        errors.add(error.getObjectName() + ": " + error.getDefaultMessage());
    }

    ApiError apiError =
      new ApiError(HttpStatus.BAD_REQUEST, ex.getLocalizedMessage(), errors);
    return handleExceptionInternal(
      ex, apiError, headers, apiError.getStatus(), request);
}

请注意，我们正在重写 ResponseEntityExceptionHandler 的基本方法并提供我们自己的自定义实现。情况并非总是如此。有时，我们需要处理基类中没有默认实现的自定义异常，稍后我们将在这里看到。

下一个：

MissingServletRequestPartException – 当未找到多部分请求的一部分时引发此异常。
MissingServletRequestParameterException – 当请求缺少参数时抛出此异常：

@Override
protected ResponseEntity<Object> handleMissingServletRequestParameter(
  MissingServletRequestParameterException ex, HttpHeaders headers,
  HttpStatus status, WebRequest request) {
    String error = ex.getParameterName() + " parameter is missing";

    ApiError apiError =
      new ApiError(HttpStatus.BAD_REQUEST, ex.getLocalizedMessage(), error);
    return new ResponseEntity<Object>(
      apiError, new HttpHeaders(), apiError.getStatus());
}

ConstraintViolationException – 此异常报告约束违规的结果：

@ExceptionHandler({ ConstraintViolationException.class })
public ResponseEntity<Object> handleConstraintViolation(
  ConstraintViolationException ex, WebRequest request) {
    List<String> errors = new ArrayList<String>();
    for (ConstraintViolation<?> violation : ex.getConstraintViolations()) {
        errors.add(violation.getRootBeanClass().getName() + " " +
          violation.getPropertyPath() + ": " + violation.getMessage());
    }

    ApiError apiError =
      new ApiError(HttpStatus.BAD_REQUEST, ex.getLocalizedMessage(), errors);
    return new ResponseEntity<Object>(
      apiError, new HttpHeaders(), apiError.getStatus());
}

TypeMismatchException – 当尝试设置错误类型的 bean 属性时抛出此异常。
MethodArgumentTypeMismatchException – 当方法参数不是预期类型时抛出此异常：

@ExceptionHandler({ MethodArgumentTypeMismatchException.class })
public ResponseEntity<Object> handleMethodArgumentTypeMismatch(
  MethodArgumentTypeMismatchException ex, WebRequest request) {
    String error =
      ex.getName() + " should be of type " + ex.getRequiredType().getName();

    ApiError apiError =
      new ApiError(HttpStatus.BAD_REQUEST, ex.getLocalizedMessage(), error);
    return new ResponseEntity<Object>(
      apiError, new HttpHeaders(), apiError.getStatus());
}

3.2.从客户端使用 API

现在让我们看一下遇到 MethodArgumentTypeMismatchException 的测试。

我们将发送一个 id 为 String 而不是 long 的请求：

@Test
public void whenMethodArgumentMismatch_thenBadRequest() {
    Response response = givenAuth().get(URL_PREFIX + "/api/foos/ccc");
    ApiError error = response.as(ApiError.class);

    assertEquals(HttpStatus.BAD_REQUEST, error.getStatus());
    assertEquals(1, error.getErrors().size());
    assertTrue(error.getErrors().get(0).contains("should be of type"));
}

最后，考虑到同样的请求：

Request method: GET
Request path: http://localhost:8080/spring-security-rest/api/foos/ccc

此类 JSON 错误响应如下所示：

{
    "status": "BAD_REQUEST",
    "message":
      "Failed to convert value of type [java.lang.String]
       to required type [java.lang.Long]; nested exception
       is java.lang.NumberFormatException: For input string: \"ccc\"",
    "errors": [
        "id should be of type java.lang.Long"
    ]
}

4. 处理 NoHandlerFoundException

接下来，我们可以自定义 servlet 来抛出此异常，而不是发送 404 响应：

<servlet>
    <servlet-name>api</servlet-name>
    <servlet-class>
      org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <init-param>
        <param-name>throwExceptionIfNoHandlerFound</param-name>
        <param-value>true</param-value>
    </init-param>
</servlet>

然后，一旦发生这种情况，我们可以像处理任何其他异常一样简单地处理它：

@Override
protected ResponseEntity<Object> handleNoHandlerFoundException(
  NoHandlerFoundException ex, HttpHeaders headers, HttpStatus status, WebRequest request) {
    String error = "No handler found for " + ex.getHttpMethod() + " " + ex.getRequestURL();

    ApiError apiError = new ApiError(HttpStatus.NOT_FOUND, ex.getLocalizedMessage(), error);
    return new ResponseEntity<Object>(apiError, new HttpHeaders(), apiError.getStatus());
}

这是一个简单的测试：

@Test
public void whenNoHandlerForHttpRequest_thenNotFound() {
    Response response = givenAuth().delete(URL_PREFIX + "/api/xx");
    ApiError error = response.as(ApiError.class);

    assertEquals(HttpStatus.NOT_FOUND, error.getStatus());
    assertEquals(1, error.getErrors().size());
    assertTrue(error.getErrors().get(0).contains("No handler found"));
}让我们看一下完整的请求：

Request method: DELETE
Request path: http://localhost:8080/spring-security-rest/api/xx

以及错误 JSON 响应：

{
    "status":"NOT_FOUND",
    "message":"No handler found for DELETE /spring-security-rest/api/xx",
    "errors":[
        "No handler found for DELETE /spring-security-rest/api/xx"
    ]
}

接下来，我们将看看另一个有趣的异常。

5. 处理 HttpRequestMethodNotSupportedException

当我们使用不受支持的 HTTP 方法发送请求时，会发生 HttpRequestMethodNotSupportedException：

@Override
protected ResponseEntity<Object> handleHttpRequestMethodNotSupported(
  HttpRequestMethodNotSupportedException ex,
  HttpHeaders headers,
  HttpStatus status,
  WebRequest request) {
    StringBuilder builder = new StringBuilder();
    builder.append(ex.getMethod());
    builder.append(
      " method is not supported for this request. Supported methods are ");
    ex.getSupportedHttpMethods().forEach(t -> builder.append(t + " "));

    ApiError apiError = new ApiError(HttpStatus.METHOD_NOT_ALLOWED,
      ex.getLocalizedMessage(), builder.toString());
    return new ResponseEntity<Object>(
      apiError, new HttpHeaders(), apiError.getStatus());
}

这是一个重现此异常的简单测试：

@Test
public void whenHttpRequestMethodNotSupported_thenMethodNotAllowed() {
    Response response = givenAuth().delete(URL_PREFIX + "/api/foos/1");
    ApiError error = response.as(ApiError.class);

    assertEquals(HttpStatus.METHOD_NOT_ALLOWED, error.getStatus());
    assertEquals(1, error.getErrors().size());
    assertTrue(error.getErrors().get(0).contains("Supported methods are"));
}

这是完整的请求：

Request method: DELETE
Request path: http://localhost:8080/spring-security-rest/api/foos/1

以及错误 JSON 响应：

{
    "status":"METHOD_NOT_ALLOWED",
    "message":"Request method 'DELETE' not supported",
    "errors":[
        "DELETE method is not supported for this request. Supported methods are GET "
    ]
}

6. 处理 HttpMediaTypeNotSupportedException

现在让我们处理 HttpMediaTypeNotSupportedException，当客户端发送不支持的媒体类型的请求时会发生该异常：

@Override
protected ResponseEntity<Object> handleHttpMediaTypeNotSupported(
  HttpMediaTypeNotSupportedException ex,
  HttpHeaders headers,
  HttpStatus status,
  WebRequest request) {
    StringBuilder builder = new StringBuilder();
    builder.append(ex.getContentType());
    builder.append(" media type is not supported. Supported media types are ");
    ex.getSupportedMediaTypes().forEach(t -> builder.append(t + ", "));

    ApiError apiError = new ApiError(HttpStatus.UNSUPPORTED_MEDIA_TYPE,
      ex.getLocalizedMessage(), builder.substring(0, builder.length() - 2));
    return new ResponseEntity<Object>(
      apiError, new HttpHeaders(), apiError.getStatus());
}

这是针对此问题的简单测试：

@Test
public void whenSendInvalidHttpMediaType_thenUnsupportedMediaType() {
    Response response = givenAuth().body("").post(URL_PREFIX + "/api/foos");
    ApiError error = response.as(ApiError.class);

    assertEquals(HttpStatus.UNSUPPORTED_MEDIA_TYPE, error.getStatus());
    assertEquals(1, error.getErrors().size());
    assertTrue(error.getErrors().get(0).contains("media type is not supported"));
}

最后，这是一个示例请求：

Request method: POST
Request path: http://localhost:8080/spring-security-
Headers: Content-Type=text/plain; charset=ISO-8859-1

以及错误 JSON 响应：

{
    "status":"UNSUPPORTED_MEDIA_TYPE",
    "message":"Content type 'text/plain;charset=ISO-8859-1' not supported",
    "errors":["text/plain;charset=ISO-8859-1 media type is not supported.
       Supported media types are text/xml
       application/x-www-form-urlencoded
       application/*+xml
       application/json;charset=UTF-8
       application/*+json;charset=UTF-8 */"
    ]
}

7. 默认处理程序

最后，我们将实现一个后备处理程序 - 一种包罗万象的逻辑类型，用于处理没有特定处理程序的所有其他异常：

@ExceptionHandler({ Exception.class })
public ResponseEntity<Object> handleAll(Exception ex, WebRequest request) {
    ApiError apiError = new ApiError(
      HttpStatus.INTERNAL_SERVER_ERROR, ex.getLocalizedMessage(), "error occurred");
    return new ResponseEntity<Object>(
      apiError, new HttpHeaders(), apiError.getStatus());
}

8.结论

为 Spring REST API 构建适当、成熟的错误处理程序非常困难，而且绝对是一个迭代过程。希望本教程将是一个良好的起点，也是帮助 API 客户端快速轻松地诊断错误并克服错误的良好锚点。

本教程的完整实现可以在 GitHub 项目中找到。这是一个基于 Eclipse 的项目，因此应该很容易导入并按原样运行。

原文链接：https://www.baeldung.com/global-error-handler-in-a-spring-rest-api