SpringBoot 错误处理机制与自定义错误处理实现详解

【1】SpringBoot的默认错误处理

① 浏览器访问

请求头如下：

② 使用“PostMan”访问

{
  "timestamp": 1529479254647,
  "status": 404,
  "error": "Not Found",
  "message": "No message available",
  "path": "/aaa1"
}

请求头如下：

总结：如果是浏览器访问，则SpringBoot默认返回错误页面；如果是其他客户端访问，则默认返回JSON数据。

【2】默认错误处理原理

SpringBoot默认配置了许多xxxAutoConfiguration，这里我们找ErrorMvcAutoConfiguration。

其注册部分组件如下：

① DefaultErrorAttributes

@Bean
@ConditionalOnMissingBean(value = ErrorAttributes.class, search = SearchStrategy.CURRENT)
public DefaultErrorAttributes errorAttributes() {
  return new DefaultErrorAttributes();
}

跟踪其源码如下：

public class DefaultErrorAttributes
    implements ErrorAttributes, HandlerExceptionResolver, Ordered {

  private static final String ERROR_ATTRIBUTE = DefaultErrorAttributes.class.getName()
      + ".ERROR";

  @Override
  public int getOrder() {
    return Ordered.HIGHEST_PRECEDENCE;
  }

  @Override
  public ModelAndView resolveException(HttpServletRequest request,
      HttpServletResponse response, Object handler, Exception ex) {
    storeErrorAttributes(request, ex);
    return null;
  }

  private void storeErrorAttributes(HttpServletRequest request, Exception ex) {
    request.setAttribute(ERROR_ATTRIBUTE, ex);
  }

  @Override
  public Map<String, Object> getErrorAttributes(RequestAttributes requestAttributes,
      boolean includeStackTrace) {
    Map<String, Object> errorAttributes = new LinkedHashMap<String, Object>();
    errorAttributes.put("timestamp", new Date());
    addStatus(errorAttributes, requestAttributes);
    addErrorDetails(errorAttributes, requestAttributes, includeStackTrace);
    addPath(errorAttributes, requestAttributes);
    return errorAttributes;
  }

  private void addStatus(Map<String, Object> errorAttributes,
      RequestAttributes requestAttributes) {
    Integer status = getAttribute(requestAttributes,
        "javax.servlet.error.status_code");
    if (status == null) {
      errorAttributes.put("status", 999);
      errorAttributes.put("error", "None");
      return;
    }
    errorAttributes.put("status", status);
    try {
      errorAttributes.put("error", HttpStatus.valueOf(status).getReasonPhrase());
    }
    catch (Exception ex) {
      // Unable to obtain a reason
      errorAttributes.put("error", "Http Status " + status);
    }
  }

  private void addErrorDetails(Map<String, Object> errorAttributes,
      RequestAttributes requestAttributes, boolean includeStackTrace) {
    Throwable error = getError(requestAttributes);
    if (error != null) {
      while (error instanceof ServletException && error.getCause() != null) {
        error = ((ServletException) error).getCause();
      }
      errorAttributes.put("exception", error.getClass().getName());
      addErrorMessage(errorAttributes, error);
      if (includeStackTrace) {
        addStackTrace(errorAttributes, error);
      }
    }
    Object message = getAttribute(requestAttributes, "javax.servlet.error.message");
    if ((!StringUtils.isEmpty(message) || errorAttributes.get("message") == null)
        && !(error instanceof BindingResult)) {
      errorAttributes.put("message",
          StringUtils.isEmpty(message) ? "No message available" : message);
    }
  }

  private void addErrorMessage(Map<String, Object> errorAttributes, Throwable error) {
    BindingResult result = extractBindingResult(error);
    if (result == null) {
      errorAttributes.put("message", error.getMessage());
      return;
    }
    if (result.getErrorCount() > 0) {
      errorAttributes.put("errors", result.getAllErrors());
      errorAttributes.put("message",
          "Validation failed for object='" + result.getObjectName()
              + "'. Error count: " + result.getErrorCount());
    }
    else {
      errorAttributes.put("message", "No errors");
    }
  }

  private BindingResult extractBindingResult(Throwable error) {
    if (error instanceof BindingResult) {
      return (BindingResult) error;
    }
    if (error instanceof MethodArgumentNotValidException) {
      return ((MethodArgumentNotValidException) error).getBindingResult();
    }
    return null;
  }

  private void addStackTrace(Map<String, Object> errorAttributes, Throwable error) {
    StringWriter stackTrace = new StringWriter();
    error.printStackTrace(new PrintWriter(stackTrace));
    stackTrace.flush();
    errorAttributes.put("trace", stackTrace.toString());
  }

  private void addPath(Map<String, Object> errorAttributes,
      RequestAttributes requestAttributes) {
    String path = getAttribute(requestAttributes, "javax.servlet.error.request_uri");
    if (path != null) {
      errorAttributes.put("path", path);
    }
  }

  @Override
  public Throwable getError(RequestAttributes requestAttributes) {
    Throwable exception = getAttribute(requestAttributes, ERROR_ATTRIBUTE);
    if (exception == null) {
      exception = getAttribute(requestAttributes, "javax.servlet.error.exception");
    }
    return exception;
  }

  @SuppressWarnings("unchecked")
  private <T> T getAttribute(RequestAttributes requestAttributes, String name) {
    return (T) requestAttributes.getAttribute(name, RequestAttributes.SCOPE_REQUEST);
  }

}

即，填充错误数据！

② BasicErrorController

@Bean
@ConditionalOnMissingBean(value = ErrorController.class, search = SearchStrategy.CURRENT)
public BasicErrorController basicErrorController(ErrorAttributes errorAttributes) {
  return new BasicErrorController(errorAttributes, this.serverProperties.getError(),
      this.errorViewResolvers);
}

跟踪其源码：

@Controller
@RequestMapping("${server.error.path:${error.path:/error}}")
public class BasicErrorController extends AbstractErrorController {
  //产生html类型的数据；浏览器发送的请求来到这个方法处理
  @RequestMapping(produces = "text/html")
  public ModelAndView errorHtml(HttpServletRequest request,
      HttpServletResponse response) {
    HttpStatus status = getStatus(request);
    Map<String, Object> model = Collections.unmodifiableMap(getErrorAttributes(
        request, isIncludeStackTrace(request, MediaType.TEXT_HTML)));
    response.setStatus(status.value());
    //去哪个页面作为错误页面；包含页面地址和页面内容
    ModelAndView modelAndView = resolveErrorView(request, response, status, model);
    return (modelAndView == null ? new ModelAndView("error", model) : modelAndView);
  }
  //产生json数据，其他客户端来到这个方法处理；
  @RequestMapping
  @ResponseBody
  public ResponseEntity<Map<String, Object>> error(HttpServletRequest request) {
    Map<String, Object> body = getErrorAttributes(request,
        isIncludeStackTrace(request, MediaType.ALL));
    HttpStatus status = getStatus(request);
    return new ResponseEntity<Map<String, Object>>(body, status);
  }
  //...
}

其中 resolveErrorView(request, response, status, model);方法跟踪如下：

public abstract class AbstractErrorController implements ErrorController {
protected ModelAndView resolveErrorView(HttpServletRequest request,
      HttpServletResponse response, HttpStatus status, Map<String, Object> model) {
      //拿到所有的错误视图解析器
    for (ErrorViewResolver resolver : this.errorViewResolvers) {
      ModelAndView modelAndView = resolver.resolveErrorView(request, status, model);
      if (modelAndView != null) {
        return modelAndView;
      }
    }
    return null;
  }
//...
}

③ ErrorPageCustomizer

@Bean
public ErrorPageCustomizer errorPageCustomizer() {
  return new ErrorPageCustomizer(this.serverProperties);
}

跟踪其源码：

@Override
public void registerErrorPages(ErrorPageRegistry errorPageRegistry) {
  ErrorPage errorPage = new ErrorPage(this.properties.getServletPrefix()
      + this.properties.getError().getPath());
  errorPageRegistry.addErrorPages(errorPage);
}
//getPath()->go on
  /**
   * Path of the error controller.
   */
  @Value("${error.path:/error}")
  private String path = "/error";

即，系统出现错误以后来到error请求进行处理（web.xml注册的错误页面规则）。

④ DefaultErrorViewResolver

@Bean
@ConditionalOnBean(DispatcherServlet.class)
@ConditionalOnMissingBean
public DefaultErrorViewResolver conventionErrorViewResolver() {
  return new DefaultErrorViewResolver(this.applicationContext,
      this.resourceProperties);
}

跟踪其源码：

public class DefaultErrorViewResolver implements ErrorViewResolver, Ordered {

  private static final Map<Series, String> SERIES_VIEWS;
  //错误状态码
  static {
    Map<Series, String> views = new HashMap<Series, String>();
    views.put(Series.CLIENT_ERROR, "4xx");
    views.put(Series.SERVER_ERROR, "5xx");
    SERIES_VIEWS = Collections.unmodifiableMap(views);
  }
  //...
  @Override
  public ModelAndView resolveErrorView(HttpServletRequest request, HttpStatus status,
      Map<String, Object> model) {
  // 这里如果没有拿到精确状态码(如404)的视图，则尝试拿4XX(或5XX)的视图
    ModelAndView modelAndView = resolve(String.valueOf(status), model);
    if (modelAndView == null && SERIES_VIEWS.containsKey(status.series())) {
      modelAndView = resolve(SERIES_VIEWS.get(status.series()), model);
    }
    return modelAndView;
  }

  private ModelAndView resolve(String viewName, Map<String, Object> model) {
    //默认SpringBoot可以去找到一个页面？ error/404||error/4xx
    String errorViewName = "error/" + viewName;
    //模板引擎可以解析这个页面地址就用模板引擎解析
    TemplateAvailabilityProvider provider = this.templateAvailabilityProviders
        .getProvider(errorViewName, this.applicationContext);
    if (provider != null) {
      //模板引擎可用的情况下返回到errorViewName指定的视图地址
      return new ModelAndView(errorViewName, model);
    }
    //模板引擎不可用，就在静态资源文件夹下找errorViewName对应的页面 error/404.html
    return resolveResource(errorViewName, model);
  }

  private ModelAndView resolveResource(String viewName, Map<String, Object> model) {
    //从静态资源文件夹下面找错误页面
    for (String location : this.resourceProperties.getStaticLocations()) {
      try {
        Resource resource = this.applicationContext.getResource(location);
        resource = resource.createRelative(viewName + ".html");
        if (resource.exists()) {
          return new ModelAndView(new HtmlResourceView(resource), model);
        }
      }
      catch (Exception ex) {
      }
    }
    return null;
  }

总结如下：

一但系统出现4xx或者5xx之类的错误，ErrorPageCustomizer就会生效（定制错误的响应规则），就会来到/error请求，然后被BasicErrorController处理返回ModelAndView或者JSON。

【3】定制错误响应

① 定制错误响应页面

1）有模板引擎的情况下

error/状态码–将错误页面命名为 错误状态码.html 放在模板引擎文件夹里面的error文件夹下，发生此状态码的错误就会来到 对应的页面。

我们可以使用4xx和5xx作为错误页面的文件名来匹配这种类型的所有错误，精确优先（优先寻找精确的状态码.html）。

如下图所示：

页面能获取的信息；

timestamp：时间戳
status：状态码
error：错误提示
exception：异常对象
message：异常消息
errors：JSR303数据校验的错误都在这里

2）没有模板引擎（模板引擎找不到这个错误页面），静态资源文件夹下找。

3）以上都没有错误页面，就是默认来到SpringBoot默认的错误提示页面。

WebMVCAutoConfiguration源码如下：

@Configuration
@ConditionalOnProperty(prefix = "server.error.whitelabel", name = "enabled", matchIfMissing = true)
@Conditional(ErrorTemplateMissingCondition.class)
protected static class WhitelabelErrorViewConfiguration {

  private final SpelView defaultErrorView = new SpelView(
      "<html><body><h1>Whitelabel Error Page</h1>"
          + "<p>This application has no explicit mapping for /error, so you are seeing this as a fallback.</p>"
          + "<div id='created'>${timestamp}</div>"
          + "<div>There was an unexpected error (type=${error}, status=${status}).</div>"
          + "<div>${message}</div></body></html>");

  @Bean(name = "error")
  @ConditionalOnMissingBean(name = "error")
  public View defaultErrorView() {
    return this.defaultErrorView;
  }

  // If the user adds @EnableWebMvc then the bean name view resolver from
  // WebMvcAutoConfiguration disappears, so add it back in to avoid disappointment.
  @Bean
  @ConditionalOnMissingBean(BeanNameViewResolver.class)
  public BeanNameViewResolver beanNameViewResolver() {
    BeanNameViewResolver resolver = new BeanNameViewResolver();
    resolver.setOrder(Ordered.LOWEST_PRECEDENCE - 10);
    return resolver;
  }

}

② 定制错误响应数据

第一种，使用SpringMVC的异常处理器

@ControllerAdvice
public class MyExceptionHandler {

  //浏览器客户端返回的都是json
  @ResponseBody
  @ExceptionHandler(UserNotExistException.class)
  public Map<String,Object> handleException(Exception e){
    Map<String,Object> map = new HashMap<>();
    map.put("code","user.notexist");
    map.put("message",e.getMessage());
    return map;
  }
}

这样无论浏览器还是PostMan返回的都是JSON！

第二种，转发到/error请求进行自适应效果处理

 @ExceptionHandler(UserNotExistException.class)
 public String handleException(Exception e, HttpServletRequest request){
    Map<String,Object> map = new HashMap<>();
    //传入我们自己的错误状态码 4xx 5xx
    /**
    * Integer statusCode = (Integer) request
    .getAttribute("javax.servlet.error.status_code");
    */
    request.setAttribute("javax.servlet.error.status_code",500);
    map.put("code","user.notexist");
    map.put("message","用户出错啦");
    //转发到/error
    return "forward:/error";
  }

但是此时没有将自定义 code message传过去！

第三种，注册MyErrorAttributes继承自DefaultErrorAttributes(推荐)

从第【2】部分(默认错误处理原理)中知道错误数据都是通过DefaultErrorAttributes.getErrorAttributes()方法获取，如下所示：

  @Override
  public Map<String, Object> getErrorAttributes(RequestAttributes requestAttributes,
      boolean includeStackTrace) {
    Map<String, Object> errorAttributes = new LinkedHashMap<String, Object>();
    errorAttributes.put("timestamp", new Date());
    addStatus(errorAttributes, requestAttributes);
    addErrorDetails(errorAttributes, requestAttributes, includeStackTrace);
    addPath(errorAttributes, requestAttributes);
    return errorAttributes;
  }

我们可以编写一个MyErrorAttributes继承自DefaultErrorAttributes重写其getErrorAttributes方法将我们的错误数据添加进去。

示例如下：

//给容器中加入我们自己定义的ErrorAttributes
@Component
public class MyErrorAttributes extends DefaultErrorAttributes {

  //返回值的map就是页面和json能获取的所有字段
  @Override
  public Map<String, Object> getErrorAttributes(RequestAttributes requestAttributes, boolean includeStackTrace) {
    //DefaultErrorAttributes的错误数据
    Map<String, Object> map = super.getErrorAttributes(requestAttributes, includeStackTrace);
    map.put("company","SpringBoot");
    //我们的异常处理器携带的数据
    Map<String,Object> ext = (Map<String, Object>) requestAttributes.getAttribute("ext", 0);
    map.put("ext",ext);
    return map;
  }
}

异常处理器修改如下：

@ExceptionHandler(UserNotExistException.class)
public String handleException(Exception e, HttpServletRequest request){
   Map<String,Object> map = new HashMap<>();
   //传入我们自己的错误状态码 4xx 5xx
   /**
   * Integer statusCode = (Integer) request
   .getAttribute("javax.servlet.error.status_code");
   */
   request.setAttribute("javax.servlet.error.status_code",500);
   map.put("code","user.notexist");
   map.put("message","用户出错啦");
  //将自定义错误数据放入request中
   request.setAttribute("ext",map);
   //转发到/error
   return "forward:/error";
 }

5xx.html页面代码如下：

//...
<main role="main" class="col-md-9 ml-sm-auto col-lg-10 pt-3 px-4">
  <h1>status:[[${status}]]</h1>
  <h2>timestamp:[[${timestamp}]]</h2>
  <h2>exception:[[${exception}]]</h2>
  <h2>message:[[${message}]]</h2>
  <h2>ext:[[${ext.code}]]</h2>
  <h2>ext:[[${ext.message}]]</h2>
</main>
//...

浏览器测试效果如下：

Postman测试效果如下：

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持我们。