SpringBoot自动装配--ErrorMvcAutoConfiguration

简介

Springboot项目在启动的时候，会自动装配一些常用的配置类（xxxAuoConfiguration），今天就来看一下和error有关的自动装配

ErrorMvcAutoConfiguration

@Configuration
@ConditionalOnWebApplication(type = Type.SERVLET)
@ConditionalOnClass({ Servlet.class, DispatcherServlet.class })
// Load before the main WebMvcAutoConfiguration so that the error View is available
@AutoConfigureBefore(WebMvcAutoConfiguration.class)
@EnableConfigurationProperties({ ServerProperties.class, ResourceProperties.class })
public class ErrorMvcAutoConfiguration {}

ErrorMvcAutoConfiguration中有以下的组件：

DefaultErrorAttributes

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

DefaultErrorAttributes中有个getErrorAttributes方法，是用于获取错误信息的

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

ErrorPageCustomizer

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

其中主要有个registerErrorPages,这就是获取错误页面路径的方法。会返回一个
path=/error,所以springboot默认会跳转到/error

@Override
public void registerErrorPages(ErrorPageRegistry errorPageRegistry) {
  ErrorPage errorPage = new ErrorPage(
      this.properties.getServlet().getServletPrefix()
          + this.properties.getError().getPath());
  errorPageRegistry.addErrorPages(errorPage);
}

DefaultErrorViewResolver

@Configuration
static class DefaultErrorViewResolverConfiguration {

  private final ApplicationContext applicationContext;

  private final ResourceProperties resourceProperties;

  DefaultErrorViewResolverConfiguration(ApplicationContext applicationContext,
      ResourceProperties resourceProperties) {
    this.applicationContext = applicationContext;
    this.resourceProperties = resourceProperties;
  }

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

}

默认的错误页面解析器,其中的主要方法

@Override
public ModelAndView resolveErrorView(HttpServletRequest request, HttpStatus status,
    Map<String, Object> model) {
  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) {
  //错误页面的名称 error/状态码
  String errorViewName = "error/" + viewName;
  //Get the provider that can be used to render the given view.
  TemplateAvailabilityProvider provider = this.templateAvailabilityProviders
      .getProvider(errorViewName, this.applicationContext);
  if (provider != null) {
    return new ModelAndView(errorViewName, model);
  }
  //否则，就到静态资源中取找
  return resolveResource(errorViewName, model);
}

private ModelAndView resolveResource(String viewName, Map<String, Object> model) {
  //遍历一下静态资源的地址，看看是否存在错误页面
  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;
}

WhitelabelErrorViewConfiguration

@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;
  }

}

这个就是默认的白页，当没有自定义的error页面时，springboot默认会使用白页。如果在template中存在了error.html,就不会注册这个bean

BasicErrorController

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

BasicErrorController是默认处理/error请求的。其中有两个主要的方法

@Controller
@RequestMapping("${server.error.path:${error.path:/error}}")
public class BasicErrorController extends AbstractErrorController {
//返回的是页面，一般是浏览器发送的请求
@RequestMapping(produces = "text/html")
	public ModelAndView errorHtml(HttpServletRequest request,
			HttpServletResponse response) {
		HttpStatus status = getStatus(request);
    //获取异常的信息，其中的getErrorAttributes就是DefaultErrorAttributes中的方法
    Map<String, Object> model = Collections.unmodifiableMap(getErrorAttributes(
  				request, isIncludeStackTrace(request, MediaType.TEXT_HTML)));
		response.setStatus(status.value());
    //获取页面，就是使用DefaultErrorViewResolver中的方法
		ModelAndView modelAndView = resolveErrorView(request, response, status, model);
    //如果modeAndView是null的话，就new一个，其中viewName是error,如果template中存在自定义的error.html的话就会使用自定义的，否则使用默认的白页。
		return (modelAndView == null ? new ModelAndView("error", model) : modelAndView);
	}
//返回的是json数据
	@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<>(body, status);
	}
}