简单认识springboot的错误处理机制

1.Spring Boot默认的错误处理机制

默认的处理效果：

1. 浏览器返回一个错误页面404
2. 如果是其他客户端，默认响应一个json数据

原理：ErrorMvcAutoConfiguration错误处理的自动配置

给容器添加了一下组件：

//ErrorAttributes,容器中没有这个组件则自动配置一个DefaultErrorAttributes，即我们看见的错误处理
@Bean
@ConditionalOnMissingBean(
    value = {ErrorAttributes.class},
    search = SearchStrategy.CURRENT
)
public DefaultErrorAttributes errorAttributes() {
    return new DefaultErrorAttributes();
}
//ErrorController
 @Bean
    @ConditionalOnMissingBean(
        value = {ErrorController.class},
        search = SearchStrategy.CURRENT
    )
    public BasicErrorController basicErrorController(ErrorAttributes errorAttributes, ObjectProvider<ErrorViewResolver> errorViewResolvers) {
        return new BasicErrorController(errorAttributes, this.serverProperties.getError(), (List)errorViewResolvers.orderedStream().collect(Collectors.toList()));
    }
//ErrorPageCustomizer
    @Bean
    public ErrorMvcAutoConfiguration.ErrorPageCustomizer errorPageCustomizer(DispatcherServletPath dispatcherServletPath) {
        return new ErrorMvcAutoConfiguration.ErrorPageCustomizer(this.serverProperties, dispatcherServletPath);
    }
//DefaultErrorViewResolver
@Bean
        @ConditionalOnBean({DispatcherServlet.class})
        @ConditionalOnMissingBean({ErrorViewResolver.class})
        DefaultErrorViewResolver conventionErrorViewResolver() {
            return new DefaultErrorViewResolver(this.applicationContext, this.resourceProperties);
        }

步骤：

​ 一旦系统出现4xx或者5xx之类的错误，ErrorPageCustomizer就会生效（定制错误的响应规则），就会被BasicErrorController处理

​ 响应页面：去哪个页面是由DefaultErrorViewResolver解析得到的;通过DefaultErrorAttributes获得错误页面可共享的信息：

​ Status：状态码

​ exception：异常对象

​ message：异常消息

​ error ：错误提示

​ timestamp：时间戳

​ errors：jsr303校验的错误

源码如下：

1. DefaultErrorAttributes

   //帮我们在页面共享信息
       public Map<String, Object> getErrorAttributes(WebRequest webRequest, ErrorAttributeOptions options) {
           Map<String, Object> errorAttributes = this.getErrorAttributes(webRequest, options.isIncluded(Include.STACK_TRACE));　　　
           if (this.includeException != null) {
               options = options.including(new Include[]{Include.EXCEPTION});
           }
           if (!options.isIncluded(Include.EXCEPTION)) {
               errorAttributes.remove("exception");
           }
           if (!options.isIncluded(Include.STACK_TRACE)) {
               errorAttributes.remove("trace");
           }
           if (!options.isIncluded(Include.MESSAGE) && errorAttributes.get("message") != null) {
               errorAttributes.put("message", "");
           }
           if (!options.isIncluded(Include.BINDING_ERRORS)) {
               errorAttributes.remove("errors");
           }
           return errorAttributes;
       }
   
       public Map<String, Object> getErrorAttributes(WebRequest webRequest, boolean includeStackTrace) {
           Map<String, Object> errorAttributes = new LinkedHashMap();
           errorAttributes.put("timestamp", new Date());
           this.addStatus(errorAttributes, webRequest);
           this.addErrorDetails(errorAttributes, webRequest, includeStackTrace);
           this.addPath(errorAttributes, webRequest);
           return errorAttributes;
       }
   

2. BasicErrorController

   @Controller
   @RequestMapping({"${server.error.path:${error.path:/error}}"})
   public class BasicErrorController extends AbstractErrorController {
   //响应ErrorPageCustomizer发出的错误请求，${server.error.path:${error.path:/error}}如果有配置文件中配置路径，也能获取
       
       
       //浏览器发送的请求请求头带有text/html，会来到这个方法处理
        @RequestMapping(
           produces = {"text/html"}   //返回html格式
       )
       public ModelAndView errorHtml(HttpServletRequest request, HttpServletResponse response) {
           HttpStatus status = this.getStatus(request);
           Map<String, Object> model = Collections.unmodifiableMap(this.getErrorAttributes(request, this.getErrorAttributeOptions(request, MediaType.TEXT_HTML)));
           response.setStatus(status.value());
           //ModelAndView  ： 获得去往那个页面作为错误页面
           ModelAndView modelAndView = this.resolveErrorView(request, response, status, model);
           return modelAndView != null ? modelAndView : new ModelAndView("error", model);
       }
   
       //其他的设备请求头不会有text/html，就来到这个方法
       @RequestMapping   //ResponseEntity相应体力是map,list,javabean，输出格式也是json
       public ResponseEntity<Map<String, Object>> error(HttpServletRequest request) {
           HttpStatus status = this.getStatus(request);
           if (status == HttpStatus.NO_CONTENT) {
               return new ResponseEntity(status);
           } else {
               Map<String, Object> body = this.getErrorAttributes(request, this.getErrorAttributeOptions(request, MediaType.ALL));
               return new ResponseEntity(body, status);
           }
       }
   

3. ErrorPageCustomizer

      @Value("${error.path:/error}")
       private String path = "/error";
   系统出现错误以后，来到error请求进行处理；
   

4. DefaultErrorViewResolver

   protected ModelAndView resolveErrorView(HttpServletRequest request, HttpServletResponse response, HttpStatus status, Map<String, Object> model) {
       Iterator var5 = this.errorViewResolvers.iterator();
   
       ModelAndView modelAndView;
       do {
           if (!var5.hasNext()) {
               return null;
           }
   			//调用ErrorViewResolver获取所有错误页面，取到对应的就返回
           ErrorViewResolver resolver = (ErrorViewResolver)var5.next();
           modelAndView = resolver.resolveErrorView(request, status, model);
       } while(modelAndView == null);
   
       return modelAndView;
   }
   

   public ModelAndView resolveErrorView(HttpServletRequest request, HttpStatus status, Map<String, Object> model) {
       ModelAndView modelAndView = this.resolve(String.valueOf(status.value()), model);
       if (modelAndView == null && SERIES_VIEWS.containsKey(status.series())) {
           modelAndView = this.resolve((String)SERIES_VIEWS.get(status.series()), model);
       }
   
       return modelAndView;
   }
   
   private ModelAndView resolve(String viewName, Map<String, Object> model) {
       //默认SpringBoot可以去到一个页面？error/404
       String errorViewName = "error/" + viewName;
       
       //模板引擎可以解析这个页面地址就用模板引擎
       TemplateAvailabilityProvider provider = this.templateAvailabilityProviders.getProvider(errorViewName, this.applicationContext);
       //模板引擎可用的情况下返回errorViewName指定的视图地址，不可用则在静态资源文件夹下找errorViewName页面
       //error/404.html
       return provider != null ? new ModelAndView(errorViewName, model) : this.resolveResource(errorViewName, model);
   }