背景
在使用SpringBoot的过程中,你肯定遇到过404错误。比如下面的代码:
@RestController @RequestMapping(value = "/hello") public class HelloWorldController { @RequestMapping("/test") public Object getObject1(HttpServletRequest request){ Response response = new Response(); response.success("请求成功..."); response.setResponseTime(); return response; } }
当我们使用错误的请求地址(POST http://127.0.0.1:8888/hello/test1?id=98)进行请求时,会报下面的错误:
{ "timestamp": "2020-11-19T08:30:48.844+0000", "status": 404, "error": "Not Found", "message": "No message available", "path": "/hello/test1" }
虽然上面的返回很清楚,但是我们的接口需要返回统一的格式,比如:
{ "rtnCode":"9999", "rtnMsg":"404 /hello/test1 Not Found" }
这时候你可能会想有Spring的统一异常处理,在Controller类上加@RestControllerAdvice注解。但是这种做法并不能统一处理404错误。
404错误产生的原因
产生404的原因是我们调了一个不存在的接口,但是为什么会返回下面的json报错呢?我们先从Spring的源代码分析下。
{ "timestamp": "2020-11-19T08:30:48.844+0000", "status": 404, "error": "Not Found", "message": "No message available", "path": "/hello/test1" }
为了代码简单起见,这边直接从DispatcherServlet的doDispatch方法开始分析。(如果不知道为什么要从这边开始,你还要熟悉下SpringMVC的源代码)。
... 省略部分代码.... // Actually invoke the handler. mv = ha.handle(processedRequest, response, mappedHandler.getHandler()); ... 省略部分代码
Spring MVC会根据请求URL的不同,配置的RequestMapping的不同,为请求匹配不同的HandlerAdapter。
对于上面的请求地址:http://127.0.0.1:8888/hello/test1?id=98匹配到的HandlerAdapter是HttpRequestHandlerAdapter。
我们直接进入到HttpRequestHandlerAdapter中看下这个类的handle方法。
@Override @Nullable public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception { ((HttpRequestHandler) handler).handleRequest(request, response); return null; }
这个方法没什么内容,直接是调用了HttpRequestHandler类的handleRequest(request, response)方法。所以直接进入这个方法看下吧。
@Override public void handleRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // For very general mappings (e.g. "/") we need to check 404 first Resource resource = getResource(request); if (resource == null) { logger.trace("No matching resource found - returning 404"); // 这个方法很简单,就是设置404响应码,然后将Response的errorState状态从0设置成1 response.sendError(HttpServletResponse.SC_NOT_FOUND); // 直接返回 return; } ... 省略部分方法 }
这个方法很简单,就是设置404响应码,将Response的errorState状态从0设置成1,然后就返回响应了。整个过程并没有发生任何异常,所以不能触发Spring的全局异常处理机制。
到这边还有一个问题没有解决:就是下面的404提示信息是怎么返回的。
{ "timestamp": "2020-11-19T08:30:48.844+0000", "status": 404, "error": "Not Found", "message": "No message available", "path": "/hello/test1" }
我们继续往下看。Response响应被返回,进入org.apache.catalina.core.StandardHostValve类的invoke方法进行处理。(不要问我为什么知道是在这里?Debug的能力是需要自己摸索出来的,自己调试多了,你也就会了)
@Override public final void invoke(Request request, Response response) throws IOException, ServletException { Context context = request.getContext(); if (context == null) { response.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR, sm.getString("standardHost.noContext")); return; } if (request.isAsyncSupported()) { request.setAsyncSupported(context.getPipeline().isAsyncSupported()); } boolean asyncAtStart = request.isAsync(); boolean asyncDispatching = request.isAsyncDispatching(); try { context.bind(Globals.IS_SECURITY_ENABLED, MY_CLASSLOADER); if (!asyncAtStart && !context.fireRequestInitEvent(request.getRequest())) { return; } try { if (!asyncAtStart || asyncDispatching) { context.getPipeline().getFirst().invoke(request, response); } else { if (!response.isErrorReportRequired()) { throw new IllegalStateException(sm.getString("standardHost.asyncStateError")); } } } catch (Throwable t) { ExceptionUtils.handleThrowable(t); container.getLogger().error("Exception Processing " + request.getRequestURI(), t); if (!response.isErrorReportRequired()) { request.setAttribute(RequestDispatcher.ERROR_EXCEPTION, t); throwable(request, response, t); } } response.setSuspended(false); Throwable t = (Throwable) request.getAttribute(RequestDispatcher.ERROR_EXCEPTION); if (!context.getState().isAvailable()) { return; } // 在这里判断请求是不是发生了错误,错误的话就进入StandardHostValve的status(Request request, Response response)方法。 // Look for (and render if found) an application level error page if (response.isErrorReportRequired()) { if (t != null) { throwable(request, response, t); } else { status(request, response); } } if (!request.isAsync() && !asyncAtStart) { context.fireRequestDestroyEvent(request.getRequest()); } } finally { // Access a session (if present) to update last accessed time, based // on a strict interpretation of the specification if (ACCESS_SESSION) { request.getSession(false); } context.unbind(Globals.IS_SECURITY_ENABLED, MY_CLASSLOADER); } }
这个方法会根据返回的响应判断是不是发生了错了,如果发生了error,则进入StandardHostValve的status(Request request, Response response)方法。这个方法“兜兜转转”又进入了StandardHostValve的custom(Request request, Response response,ErrorPage errorPage)方法。这个方法中将请求重新forward到了"/error"接口。
private boolean custom(Request request, Response response, ErrorPage errorPage) { if (container.getLogger().isDebugEnabled()) { container.getLogger().debug("Processing " + errorPage); } try { // Forward control to the specified location ServletContext servletContext = request.getContext().getServletContext(); RequestDispatcher rd = servletContext.getRequestDispatcher(errorPage.getLocation()); if (rd == null) { container.getLogger().error( sm.getString("standardHostValue.customStatusFailed", errorPage.getLocation())); return false; } if (response.isCommitted()) { rd.include(request.getRequest(), response.getResponse()); } else { // Reset the response (keeping the real error code and message) response.resetBuffer(true); response.setContentLength(-1); // 1: 重新forward请求到/error接口 rd.forward(request.getRequest(), response.getResponse()); response.setSuspended(false); } return true; } catch (Throwable t) { ExceptionUtils.handleThrowable(t); container.getLogger().error("Exception Processing " + errorPage, t); return false; } }
上面标号1处的代码重新将请求forward到了/error接口。所以如果我们开着Debug日志的话,你会在后台看到下面的日志。
[http-nio-8888-exec-7] DEBUG org.springframework.web.servlet.DispatcherServlet:891 - DispatcherServlet with name 'dispatcherServlet' processing POST request for [/error]
2020-11-19 19:04:04.280 [http-nio-8888-exec-7] DEBUG org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping:313 - Looking up handler method for path /error
2020-11-19 19:04:04.281 [http-nio-8888-exec-7] DEBUG org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping:320 - Returning handler method [public org.springframework.http.ResponseEntity<java.util.Map<java.lang.String, java.lang.Object>> org.springframework.boot.autoconfigure.web.servlet.error.BasicErrorController.error(javax.servlet.http.HttpServletRequest)]
2020-11-19 19:04:04.281 [http-nio-8888-exec-7] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory:255 - Returning cached instance of singleton bean 'basicErrorController'
上面是/error的请求日志。到这边还是没说明为什么能返回json格式的404返回格式。我们继续往下看。
到这边为止,我们好像没有任何线索了。但是如果仔细看上面日志的话,你会发现这个接口的处理方法是:
org.springframework.boot.autoconfigure.web.servlet.error.BasicErrorController.error(javax.servlet.http.HttpServletRequest)]
我们打开BasicErrorController这个类的源代码,一切豁然开朗。
@Controller @RequestMapping("${server.error.path:${error.path:/error}}") public class BasicErrorController extends AbstractErrorController { @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()); ModelAndView modelAndView = resolveErrorView(request, response, status, model); return (modelAndView == null ? new ModelAndView("error", model) : modelAndView); } @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); } ... 省略部分方法 }
BasicErrorController是Spring默认配置的一个Controller,默认处理/error请求。BasicErrorController提供两种返回错误一种是页面返回、当你是页面请求的时候就会返回页面,另外一种是json请求的时候就会返回json错误。
自定义404错误处理类
我们先看下BasicErrorController是在哪里进行配置的。
在IDEA中,查看BasicErrorController的usage,我们发现这个类是在ErrorMvcAutoConfiguration中自动配置的。
@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 { @Bean @ConditionalOnMissingBean(value = ErrorController.class, search = SearchStrategy.CURRENT) public BasicErrorController basicErrorController(ErrorAttributes errorAttributes) { return new BasicErrorController(errorAttributes, this.serverProperties.getError(), this.errorViewResolvers); } ... 省略部分代码 }
从上面的配置中可以看出来,只要我们自己配置一个ErrorController,就可以覆盖掉BasicErrorController的行为。
@Controller @RequestMapping("${server.error.path:${error.path:/error}}") public class CustomErrorController extends BasicErrorController { @Value("${server.error.path:${error.path:/error}}") private String path; public CustomErrorController(ServerProperties serverProperties) { super(new DefaultErrorAttributes(), serverProperties.getError()); } /** * 覆盖默认的JSON响应 */ @Override public ResponseEntity<Map<String, Object>> error(HttpServletRequest request) { HttpStatus status = getStatus(request); Map<String, Object> map = new HashMap<String, Object>(16); Map<String, Object> originalMsgMap = getErrorAttributes(request, isIncludeStackTrace(request, MediaType.ALL)); String path = (String)originalMsgMap.get("path"); String error = (String)originalMsgMap.get("error"); String message = (String)originalMsgMap.get("message"); StringJoiner joiner = new StringJoiner(",","[","]"); joiner.add(path).add(error).add(message); map.put("rtnCode", "9999"); map.put("rtnMsg", joiner.toString()); return new ResponseEntity<Map<String, Object>>(map, status); } /** * 覆盖默认的HTML响应 */ @Override public ModelAndView errorHtml(HttpServletRequest request, HttpServletResponse response) { //请求的状态 HttpStatus status = getStatus(request); response.setStatus(getStatus(request).value()); Map<String, Object> model = getErrorAttributes(request, isIncludeStackTrace(request, MediaType.TEXT_HTML)); ModelAndView modelAndView = resolveErrorView(request, response, status, model); //指定自定义的视图 return (modelAndView == null ? new ModelAndView("error", model) : modelAndView); } }
默认的错误路径是/error,我们可以通过以下配置进行覆盖:
server: error: path: /xxx
更详细的内容请参考Spring Boot的
简单总结#
- 如果在过滤器(Filter)中发生异常,或者调用的接口不存在,Spring会直接将Response的errorStatus状态设置成1,将http响应码设置为500或者404,Tomcat检测到errorStatus为1时,会将请求重现forward到/error接口;
- 如果请求已经进入了Controller的处理方法,这时发生了异常,如果没有配置Spring的全局异常机制,那么请求还是会被forward到/error接口,如果配置了全局异常处理,Controller中的异常会被捕获;
- 继承BasicErrorController就可以覆盖原有的错误处理方式。
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