1，大致流程
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；就会被BasicErrorController处理；
响应页面；去哪个页面是由DefaultErrorViewResolver解析得到的；2，错误自动配置类
ErrorMvcAutoConfiguration ，此类帮我们自动配置了：
@Bean public ErrorPageCustomizer errorPageCustomizer() { return new ErrorPageCustomizer(this.serverProperties); }private static class ErrorPageCustomizer implements ErrorPageRegistrar, Ordered { /*添加错误映射，即发生错误时会发送 /error 请求*/ @Override public void registerErrorPages(ErrorPageRegistry errorPageRegistry) { ErrorPage errorPage = new ErrorPage( this.properties.getServlet().getServletPrefix() + this.properties.getError().getPath()); errorPageRegistry.addErrorPages(errorPage); }}public class ErrorProperties { @Value("${error.path:/error}") private String path = "/error"; 3，BasicErrorController 处理 /error 请求
/*返回页面响应*/@RequestMapping(produces = "text/html") public ModelAndView errorHtml(HttpServletRequest request, HttpServletResponse response) { /*得到错误响应码*/ HttpStatus status = getStatus(request); /*得到错误要显示的响应数据*/ Map model = Collections.unmodifiableMap(getErrorAttributes( request, isIncludeStackTrace(request, MediaType.TEXT_HTML))); response.setStatus(status.value()); ModelAndView modelAndView = resolveErrorView(request, response, status, model); /*如果没有找到对应的 /error/5xx.html 视图 就会返回一个名为 error 的ModelAndView*/ return (modelAndView != null ? modelAndView : new ModelAndView("error", model)); }/*返回json响应*/ @RequestMapping @ResponseBody public ResponseEntity ①，getStatus
protected HttpStatus getStatus(HttpServletRequest request) { /*从request 获取key为 javax.servlet.error.status_code 的值*/ Integer statusCode = (Integer) request .getAttribute("javax.servlet.error.status_code"); if (statusCode == null) { /*获取不到就响应一个500*/ return HttpStatus.INTERNAL_SERVER_ERROR; } try { return HttpStatus.valueOf(statusCode); } catch (Exception ex) { /*发生错误也响应一个500*/ return HttpStatus.INTERNAL_SERVER_ERROR; } } ②，getErrorAttributes 获取错误响应数据
public abstract class AbstractErrorController implements ErrorController { private final ErrorAttributes errorAttributes; protected Map getErrorAttributes(HttpServletRequest request, boolean includeStackTrace) { WebRequest webRequest = new ServletWebRequest(request); /*就是调用ErrorAttributes 里的 getErrorAttributes 方法获取响应数据*/ return this.errorAttributes.getErrorAttributes(webRequest, includeStackTrace); }}public class ErrorMvcAutoConfiguration {/*为我们注册了一个DefaultErrorAttributes */@Bean @ConditionalOnMissingBean(value = ErrorAttributes.class, search = SearchStrategy.CURRENT) public DefaultErrorAttributes errorAttributes() { return new DefaultErrorAttributes( this.serverProperties.getError().isIncludeException()); }}//即调用了DefaultErrorAttributes 的 getErrorAttributes 方法，如下： @Override public Map getErrorAttributes(WebRequest webRequest, boolean includeStackTrace) { Map errorAttributes = new LinkedHashMap<>(); errorAttributes.put("timestamp", new Date()); addStatus(errorAttributes, webRequest); addErrorDetails(errorAttributes, webRequest, includeStackTrace); addPath(errorAttributes, webRequest); return errorAttributes; }/*总的来说就是放了如下数据页面能获取的信息；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*/ ③，name为error 的ModelAndView
public class ErrorMvcAutoConfiguration { @Configuration @ConditionalOnProperty(prefix = "server.error.whitelabel", name = "enabled", matchIfMissing = true) @Conditional(ErrorTemplateMissingCondition.class) protected static class WhitelabelErrorViewConfiguration { //这个即我们经常看到的错误页 private final SpelView defaultErrorView = new SpelView( "Whitelabel Error Page
" + "This application has no explicit mapping for /error, so you are seeing this as a fallback.
" + " ${timestamp} " + " There was an unexpected error (type=${error}, status=${status}). " + " ${message} "); // 即是这个View @Bean(name = "error") @ConditionalOnMissingBean(name = "error") public View defaultErrorView() { return this.defaultErrorView; }} 4，定制错误响应
①，编写一个错误处理类，这里还是用到了@ControllerAdvice 注解
import org.springframework.web.bind.annotation.ControllerAdvice;import org.springframework.web.bind.annotation.ExceptionHandler;import javax.servlet.http.HttpServletRequest;import java.util.HashMap;import java.util.Map;//声明是一个错误处理器@ControllerAdvicepublic class ErrorControllAdvice {// 处理那种类型的错误 @ExceptionHandler(Exception.class) public String errorHandle(HttpServletRequest request){// 添加额外错误响应数据 Map map=new HashMap<>();// 添加一个公司的响应数据 map.put("company","小米");// 放到request 中，然后在我们定制的DefaultErrorAttributes 里获取 request.setAttribute("ext",map);// 设置响应状态码 request.setAttribute("javax.servlet.error.status_code",500);// 转发到/error 请求，这样就能根据客户端优化接收何种类型数据，决定响应html还是json return "forward:/error"; }} ②，定制DefaultErrorAttributes
import org.springframework.boot.web.servlet.error.DefaultErrorAttributes;import org.springframework.stereotype.Component;import org.springframework.web.context.request.RequestAttributes;import org.springframework.web.context.request.WebRequest;import java.util.Map;@Componentpublic class MyDefaultErrorAttributes extends DefaultErrorAttributes { /*重写getErrorAttributes 方法*/ @Override public Map getErrorAttributes(WebRequest webRequest, boolean includeStackTrace) {// 获取原来的响应数据 Map map = super.getErrorAttributes(webRequest, includeStackTrace); //从请求域中拿值 Map ext = (Map ) webRequest.getAttribute("ext", RequestAttributes.SCOPE_REQUEST); //添加我们定制的响应数据 map.put("ext",ext);// 返回带有我们定制的数据的map return map; }} 5，测试
