Spring Boot優(yōu)雅地處理404異常
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? 作者?|??程序員自由之路
來源 |? urlify.cn/Mv2Avq
背景
在使用SpringBoot的過程中，你肯定遇到過404錯誤。比如下面的代碼：
@RestController
@RequestMapping(value?=?"/hello")
public?class?HelloWorldController?{
????@RequestMapping("/test")
????public?Object?getObject1(HttpServletRequest?request){
????????Response?response?=?new?Response();
????????response.success("請求成功...");
????????response.setResponseTime();
????????return?response;
????}
}
當我們使用錯誤的請求地址（POST http://127.0.0.1:8888/hello/test1?id=98）進行請求時，會報下面的錯誤：
{
??"timestamp":?"2020-11-19T08:30:48.844+0000",
??"status":?404,
??"error":?"Not?Found",
??"message":?"No?message?available",
??"path":?"/hello/test1"
}
雖然上面的返回很清楚，但是我們的接口需要返回統(tǒng)一的格式，比如：
{
????"rtnCode":"9999",
????"rtnMsg":"404?/hello/test1?Not?Found"
}
這時候你可能會想有Spring的統(tǒng)一異常處理，在Controller類上加@RestControllerAdvice注解。但是這種做法并不能統(tǒng)一處理404錯誤。
404錯誤產(chǎn)生的原因
產(chǎn)生404的原因是我們調(diào)了一個不存在的接口，但是為什么會返回下面的json報錯呢？我們先從Spring的源代碼分析下。
{
??"timestamp":?"2020-11-19T08:30:48.844+0000",
??"status":?404,
??"error":?"Not?Found",
??"message":?"No?message?available",
??"path":?"/hello/test1"
}
為了代碼簡單起見，這邊直接從DispatcherServlet的doDispatch方法開始分析。（如果不知道為什么要從這邊開始，你還要熟悉下SpringMVC的源代碼）。
...?省略部分代碼....
//?Actually?invoke?the?handler.
mv?=?ha.handle(processedRequest,?response,?mappedHandler.getHandler());
...?省略部分代碼
Spring MVC會根據(jù)請求URL的不同，配置的RequestMapping的不同，為請求匹配不同的HandlerAdapter。
對于上面的請求地址：http://127.0.0.1:8888/hello/test1?id=98匹配到的HandlerAdapter是HttpRequestHandlerAdapter。
我們直接進入到HttpRequestHandlerAdapter中看下這個類的handle方法。
@Override
@Nullable
public?ModelAndView?handle(HttpServletRequest?request,?HttpServletResponse?response,?Object?handler)
????throws?Exception?{
????((HttpRequestHandler)?handler).handleRequest(request,?response);
????return?null;
}
這個方法沒什么內(nèi)容，直接是調(diào)用了HttpRequestHandler類的handleRequest(request, response)方法。所以直接進入這個方法看下吧。
@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");
????????//?這個方法很簡單，就是設置404響應碼，然后將Response的errorState狀態(tài)從0設置成1
????????response.sendError(HttpServletResponse.SC_NOT_FOUND);
????????//?直接返回
????????return;
????}
????...?省略部分方法
}
這個方法很簡單，就是設置404響應碼，將Response的errorState狀態(tài)從0設置成1，然后就返回響應了。整個過程并沒有發(fā)生任何異常，所以不能觸發(fā)Spring的全局異常處理機制。
到這邊還有一個問題沒有解決：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"
}
我們繼續(xù)往下看。Response響應被返回，進入org.apache.catalina.core.StandardHostValve類的invoke方法進行處理。（不要問我為什么知道是在這里？Debug的能力是需要自己摸索出來的，自己調(diào)試多了，你也就會了）
@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;
????????}
????????//?在這里判斷請求是不是發(fā)生了錯誤，錯誤的話就進入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);
????}
??}
這個方法會根據(jù)返回的響應判斷是不是發(fā)生了錯了，如果發(fā)生了error，則進入StandardHostValve的status(Request request, Response response)方法。這個方法“兜兜轉(zhuǎn)轉(zhuǎn)”又進入了StandardHostValve的custom(Request request, Response response,ErrorPage errorPage)方法。這個方法中將請求重新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請求到/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;
????????}
????}
上面標號1處的代碼重新將請求forward到了/error接口。所以如果我們開著Debug日志的話，你會在后臺看到下面的日志。
[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>?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的請求日志。到這邊還是沒說明為什么能返回json格式的404返回格式。我們繼續(xù)往下看。
到這邊為止，我們好像沒有任何線索了。但是如果仔細看上面日志的話，你會發(fā)現(xiàn)這個接口的處理方法是：
org.springframework.boot.autoconfigure.web.servlet.error.BasicErrorController.error(javax.servlet.http.HttpServletRequest)]
我們打開BasicErrorController這個類的源代碼，一切豁然開朗。
@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?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>?error(HttpServletRequest?request)?{
????????Map?body?=?getErrorAttributes(request,
????????????????isIncludeStackTrace(request,?MediaType.ALL));
????????HttpStatus?status?=?getStatus(request);
????????return?new?ResponseEntity>(body,?status);
????}
????...?省略部分方法
}
BasicErrorController是Spring默認配置的一個Controller，默認處理/error請求。BasicErrorController提供兩種返回錯誤一種是頁面返回、當你是頁面請求的時候就會返回頁面，另外一種是json請求的時候就會返回json錯誤。
自定義404錯誤處理類
我們先看下BasicErrorController是在哪里進行配置的。
在IDEA中，查看BasicErrorController的usage，我們發(fā)現(xiàn)這個類是在ErrorMvcAutoConfiguration中自動配置的。
@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);
?}
?...?省略部分代碼
}
從上面的配置中可以看出來，只要我們自己配置一個ErrorController，就可以覆蓋掉BasicErrorController的行為。
@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());
????}
????/**
?????*?覆蓋默認的JSON響應
?????*/
????@Override
????public?ResponseEntity>?error(HttpServletRequest?request)?{
????????HttpStatus?status?=?getStatus(request);
????????Map?map?=?new?HashMap(16);
????????Map?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,?status);
????}
????/**
?????*?覆蓋默認的HTML響應
?????*/
????@Override
????public?ModelAndView?errorHtml(HttpServletRequest?request,?HttpServletResponse?response)?{
????????//請求的狀態(tài)
????????HttpStatus?status?=?getStatus(request);
????????response.setStatus(getStatus(request).value());
????????Map?model?=?getErrorAttributes(request,
????????????????isIncludeStackTrace(request,?MediaType.TEXT_HTML));
????????ModelAndView?modelAndView?=?resolveErrorView(request,?response,?status,?model);
????????//指定自定義的視圖
????????return?(modelAndView?==?null???new?ModelAndView("error",?model)?:?modelAndView);
????}
}
默認的錯誤路徑是/error，我們可以通過以下配置進行覆蓋：
server:
??error:
????path:?/xxx
更詳細的內(nèi)容請參考Spring Boot的
簡單總結(jié)
如果在過濾器（Filter）中發(fā)生異常，或者調(diào)用的接口不存在，Spring會直接將Response的errorStatus狀態(tài)設置成1，將http響應碼設置為500或者404，Tomcat檢測到errorStatus為1時，會將請求重現(xiàn)forward到/error接口；
如果請求已經(jīng)進入了Controller的處理方法，這時發(fā)生了異常，如果沒有配置Spring的全局異常機制，那么請求還是會被forward到/error接口，如果配置了全局異常處理，Controller中的異常會被捕獲；
繼承BasicErrorController就可以覆蓋原有的錯誤處理方式。
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