預設效果：
1）、瀏覽器，返回一個預設的錯誤頁面

　　1.1 請求頭

　　1.2返回結果

2）、如果是其他客戶端，預設響應一個json資料

　　2.1請求頭

　　2.2返回結果

步驟：
　　1）系統出現4xx或者5xx之類的錯誤；ErrorPageCustomizer就會生效（定製錯誤的響應規則）；

　　2） 根據相應規則來到/error請求；被BasicErrorController處理；

　　3）響應頁面；被Controller處理後去哪個頁面是由DefaultErrorViewResolver解析得到的；

原始碼解析

public class ErrorMvcAutoConfiguration {
　　 // 系統出現錯誤以後來到error請求進行處理；（相當於web.xml註冊錯誤頁面規則） 
    @Bean
    public ErrorPageCustomizer errorPageCustomizer() {
        return new ErrorPageCustomizer(this.serverProperties, this.dispatcherServletPath);
    }
    
    /**
     * {@link WebServerFactoryCustomizer} that configures the server's error pages.
     
 
*/
    private static class ErrorPageCustomizer implements ErrorPageRegistrar, Ordered {

        private final ServerProperties properties;

        private final DispatcherServletPath dispatcherServletPath;

        protected ErrorPageCustomizer(ServerProperties properties,
                DispatcherServletPath dispatcherServletPath) {
            
 
this.properties = properties;
            this.dispatcherServletPath = dispatcherServletPath;
        }

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

        @Override
        public int getOrder() {
            return 0;
        }

    }
}

public class ErrorProperties {
    /**
     * Path of the error controller.
     */
    @Value("${error.path:/error}")
    private String path = "/error";
    
}

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

}


public abstract class AbstractErrorController implements ErrorController {

    private final ErrorAttributes errorAttributes;

    private final List<ErrorViewResolver> errorViewResolvers;

    public AbstractErrorController(ErrorAttributes errorAttributes) {
        this(errorAttributes, null);
    }
    
    //解析錯誤頁面
    protected ModelAndView resolveErrorView(HttpServletRequest request,
            HttpServletResponse response, HttpStatus status, Map<String, Object> model) {
        for (ErrorViewResolver resolver : this.errorViewResolvers) {
            ModelAndView modelAndView = resolver.resolveErrorView(request, status, model);
            if (modelAndView != null) {
                return modelAndView;
            }
        }
        return null;
    }
    
}

/**取出配置項：server.error.path中的值。如果沒有，則取error.path的值，如果還沒有，則預設為/error路徑*/
@Controller
@RequestMapping("${server.error.path:${error.path:/error}}")
public class BasicErrorController extends AbstractErrorController {
    

    @RequestMapping(produces = "text/html")//產生html型別的資料；瀏覽器傳送的請求來到這個方法處理
    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());
        
        //去哪個頁面作為錯誤頁面；包含頁面地址和頁面內容
        ModelAndView modelAndView = resolveErrorView(request, response, status, model);
        return (modelAndView != null) ? modelAndView : new ModelAndView("error", model);
    }

    
    //產生json資料，其他客戶端來到這個方法處理；
    @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<>(body, status);
    }
}




public class DefaultErrorViewResolver implements ErrorViewResolver, Ordered {

    private static final Map<Series, String> SERIES_VIEWS;

　　 private final ResourceProperties resourceProperties;

    static {
        Map<Series, String> views = new EnumMap<>(Series.class);
        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) {
        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) {
        //預設SpringBoot可以去找到一個頁面？ error/404
        String errorViewName = "error/" + viewName;
        //模板引擎可以解析這個頁面地址就用模板引擎解析
        TemplateAvailabilityProvider provider = this.templateAvailabilityProviders
                .getProvider(errorViewName, this.applicationContext);
        if (provider != null) {
　　　　　　　//模板引擎可用的情況下返回到errorViewName指定的檢視地址
            return new ModelAndView(errorViewName, model);
        }
　　　　　//模板引擎不可用
        return resolveResource(errorViewName, model);
    }
　　//
    private ModelAndView resolveResource(String viewName, Map<String, Object> model) {
        //從靜態資原始檔夾下解析對應的頁面 error/404.html
        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;
    }
}

 靜態資原始檔夾路徑

@ConfigurationProperties(prefix = "spring.resources", ignoreUnknownFields = false)
public class ResourceProperties {

    private static final String[] CLASSPATH_RESOURCE_LOCATIONS = {
            "classpath:/META-INF/resources/", "classpath:/resources/",
            "classpath:/static/", "classpath:/public/" };

    /**
     * Locations of static resources. Defaults to classpath:[/META-INF/resources/,
     * /resources/, /static/, /public/].
     */
    private String[] staticLocations = CLASSPATH_RESOURCE_LOCATIONS;

}