SpringBoot - 错误处理机制与自定义错误处理实现

【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：