@ControllerAdvice注解使用及原理探究 | 京东物流技术团队

最近在新项目的开发过程中，遇到了个问题，需要将一些异常的业务流程返回给前端，需要提供给前端不同的响应码，前端再在次基础上做提示语言的国际化适配。这些异常流程涉及业务层和控制层的各个地方，如果每个地方都写一些重复代码显得很冗余。

然后查询解决方案时发现了@ControllerAdvice这个注解，可以对业务异常进行统一处理。经过仔细了解后，发现这个注解还有更多的用处，都很实用。

1 ControllerAdvice介绍

@ControllerAdvice一般和三个以下注解一块使用，起到不同的作用,

1. @ExceptionHandler: 该注解作用于方法上，，可以捕获到controller中抛出的一些自定义异常，统一进行处理，一般用于进行一些特定的异常处理。
2. @InitBinder:该注解作用于方法上,用于将前端请求的特定类型的参数在到达controller之前进行处理，从而达到转换请求参数格式的目的。
3. @ModelAttribute：该注解作用于方法和请求参数上，在方法上时设置一个值，可以直接在进入controller后传入该参数。

2 ControllerAdvice应用场景

2.1@ExceptionHandler统一处理业务异常

@RestControllerAdvice @Slf4j public class GlobalExceptionHandler { // 这里就是对各个层返回的异常进行统一捕获处理 @ExceptionHandler(value = BusinessException.class) public ResponseData<Void> bizException(BusinessException e){ log.error("业务异常记录",e); return ResponseData.error(e.getCode(),e.getMessage()); } } //业务异常处代码示例： if(CollectionUtil.isNotEmpty(companies)){ // 通过BusinessExceptionEnum枚举对业务异常进行统一管理 throw new BusinessException(BusinessExceptionEnum.ERROR_10003); } 

需要注意的是，如果这里有多个ExceptionHandler,按照异常类的层次体系，越高层的异常，优先级越低。

2.2@InitBinder做日期格式的统一处理

@RestControllerAdvice @Slf4j public class GlobalExceptionHandler { // 将前端传入的字符串时间格式转换为LocalDate时间 @InitBinder protected void initBinder(WebDataBinder binder) { //将前端传入的字符串格式时间数据转为LocalDate格式的数据 binder.registerCustomEditor(LocalDate.class, new PropertyEditorSupport() { @Override public void setAsText(String text) throws IllegalArgumentException { setValue(LocalDate.parse(text, DateTimeFormatter.ofPattern(DEFAULT_DATE_FORMAT))); } }); //将前端传入的字符串格式时间数据转为LocalDateTime格式的数据 binder.registerCustomEditor(LocalDateTime.class, new PropertyEditorSupport() { @Override public void setAsText(String text) throws IllegalArgumentException { setValue(LocalDateTime.parse(text, DateTimeFormatter.ofPattern(DEFAULT_DATE_TIME_FORMAT))); } }); //将前端传入的字符串格式时间数据转为LocalTim格式的数据 binder.registerCustomEditor(LocalTime.class, new PropertyEditorSupport() { @Override public void setAsText(String text) throws IllegalArgumentException { setValue(LocalTime.parse(text, DateTimeFormatter.ofPattern(DEFAULT_TIME_FORMAT))); } }); } } // controller进行参数绑定 public ResponseData<List<WorkCalendarVo>> listWorkCalendar(@RequestParam LocalDate date){} 

2.3 ModelAttribute提前绑定全局user对象

// 这里@ModelAttribute("loginUser")标注的modelAttribute()方法表示会在Controller方法之前将user设置到contoller里的已绑定参数里 @ModelAttribute("loginUser") public User setLoginUser(HttpServletRequest request) { return LoginContextUtils.getLoginUser(request); } // 使用 @PostMapping("/list") public ResponseData<IPage<EmployeeVo>> listEmployee(@ModelAttribute("loginUser") User user, @RequestBody EmployeeSearch employeeSearch){ return ResponseData.success(employeeService.listEmployee(user, employeeSearch)); } 

3 ControllerAdvice作用原理探究

在探究ControllerAdvice如何生效时，不得不提到springMvc绕不过的DispatcherServlet，这个类是SpringMVC统一的入口，所有的请求都通过它，里面的一些初始化方法如下。

public class DispatcherServlet extends FrameworkServlet { // ...... protected void initStrategies(ApplicationContext context) { initMultipartResolver(context); initLocaleResolver(context); initThemeResolver(context); initHandlerMappings(context); //请求处理的adapter initHandlerAdapters(context); // 异常响应处理的resolver initHandlerExceptionResolvers(context); initRequestToViewNameTranslator(context); initViewResolvers(context); initFlashMapManager(context); } // ...... } 

3.1@initBinder和@ModelAttribute的作用原理

@initBinder和@ModelAttribute都是请求过程中的处理，我们知道springMvc通过HandlerApapter定位到具体的方法进行请求处理，因此查看HandlerHaper的实现类，发现RequestMappingHandlerAdapter比较符合我们的目标

点进去RequestMappingHandlerAdapter后发现里面的一个方法如下

@Override public void afterPropertiesSet() { // Do this first, it may add ResponseBody advice beans // 这里会添加ResponseBody advice beans initControllerAdviceCache(); if (this.argumentResolvers == null) { List<HandlerMethodArgumentResolver> resolvers = getDefaultArgumentResolvers(); this.argumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers); } if (this.initBinderArgumentResolvers == null) { List<HandlerMethodArgumentResolver> resolvers = getDefaultInitBinderArgumentResolvers(); this.initBinderArgumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers); } if (this.returnValueHandlers == null) { List<HandlerMethodReturnValueHandler> handlers = getDefaultReturnValueHandlers(); this.returnValueHandlers = new HandlerMethodReturnValueHandlerComposite().addHandlers(handlers); } } // 这里找到contollerAdvice注解的类，缓存里面的方法 private void initControllerAdviceCache() { if (getApplicationContext() == null) { return; } // 找到@ControllerAdvice注解标注的类 List<ControllerAdviceBean> adviceBeans = ControllerAdviceBean.findAnnotatedBeans(getApplicationContext()); List<Object> requestResponseBodyAdviceBeans = new ArrayList<>(); for (ControllerAdviceBean adviceBean : adviceBeans) { Class<?> beanType = adviceBean.getBeanType(); if (beanType == null) { throw new IllegalStateException("Unresolvable type for ControllerAdviceBean: " + adviceBean); } // 找到所有ModelAttribute标注的方法进行缓存，就可以使用了 Set<Method> attrMethods = MethodIntrospector.selectMethods(beanType, MODEL_ATTRIBUTE_METHODS); if (!attrMethods.isEmpty()) { this.modelAttributeAdviceCache.put(adviceBean, attrMethods); } // 找到所有initBinder注解标注的方法进行缓存，就可以使用了 Set<Method> binderMethods = MethodIntrospector.selectMethods(beanType, INIT_BINDER_METHODS); if (!binderMethods.isEmpty()) { this.initBinderAdviceCache.put(adviceBean, binderMethods); } if (RequestBodyAdvice.class.isAssignableFrom(beanType) || ResponseBodyAdvice.class.isAssignableFrom(beanType)) { requestResponseBodyAdviceBeans.add(adviceBean); } } if (!requestResponseBodyAdviceBeans.isEmpty()) { this.requestResponseBodyAdvice.addAll(0, requestResponseBodyAdviceBeans); } // ......日志处理 } 

3.2@ExceptionHandler注解的作用原理

相同的思路，@ExceptionHandler是响应时的处理，因此需要找到对应的Resolver，进入initHandlerExceptionResolvers(context)方法,

属性填充后会进行afterPropertiesSet方法，这个方法可以用在一些特殊情况中，也就是某个对象的某个属性需要经过外界得到，比如说查询数据库等方式，这时候可以用到spring的该特性，只需要实现InitializingBean。

@Override public void afterPropertiesSet() { // Do this first, it may add ResponseBodyAdvice beans initExceptionHandlerAdviceCache(); if (this.argumentResolvers == null) { List<HandlerMethodArgumentResolver> resolvers = getDefaultArgumentResolvers(); this.argumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers); } if (this.returnValueHandlers == null) { List<HandlerMethodReturnValueHandler> handlers = getDefaultReturnValueHandlers(); this.returnValueHandlers = new HandlerMethodReturnValueHandlerComposite().addHandlers(handlers); } } private void initExceptionHandlerAdviceCache() { if (getApplicationContext() == null) { return; } List<ControllerAdviceBean> adviceBeans = ControllerAdviceBean.findAnnotatedBeans(getApplicationContext()); for (ControllerAdviceBean adviceBean : adviceBeans) { Class<?> beanType = adviceBean.getBeanType(); if (beanType == null) { throw new IllegalStateException("Unresolvable type for ControllerAdviceBean: " + adviceBean); } // 这里找到ExceptionHandler注解标注的方法进行缓存，后面就可以使用了 ExceptionHandlerMethodResolver resolver = new ExceptionHandlerMethodResolver(beanType); if (resolver.hasExceptionMappings()) { this.exceptionHandlerAdviceCache.put(adviceBean, resolver); } if (ResponseBodyAdvice.class.isAssignableFrom(beanType)) { this.responseBodyAdvice.add(adviceBean); } } // ......日志处理 } 

在启动spring时debug发现最终也会走到这里对@ExceptionHander注解的方法已经缓存

当Controller抛出异常时，DispatcherServlet通过ExceptionHandlerExceptionResolver来解析异常，而ExceptionHandlerExceptionResolver又通过ExceptionHandlerMethodResolver 来解析异常， ExceptionHandlerMethodResolver 最终解析异常找到适用的@ExceptionHandler标注的方法是这里：

 @Nullable public Method resolveMethodByExceptionType(Class<? extends Throwable> exceptionType) { Method method = this.exceptionLookupCache.get(exceptionType); if (method == null) { method = getMappedMethod(exceptionType); this.exceptionLookupCache.put(exceptionType, method); } return (method != NO_MATCHING_EXCEPTION_HANDLER_METHOD ? method : null); } 

4 用具体的调用过程，验证上面的推测

本部分通过对DispatcherServlet的调用过程跟踪，梳理出ControllerAdvice的作用原理，以@InitBinder主节点生效过程为例。

首选是dispathServlet在初始化过程中，初始化RequestMappingHandlerAdapter过程中打断点发现，initBinder已经缓存进来了。

然后是dispatcherServlet的调用流程图，验证下是initBinder注解是否生效。

DispatcherServlet 通过doService()方法开始调用,主要逻辑包括 设置 request ，通过doDispatch() 进行请求分发处理。

doDispatch() 的主要过程是通过 HandlerMapping 获取 Handler，再找到用于执行它的 HandlerAdapter，执行 Handler 后得到 ModelAndView ，ModelAndView 是连接“业务逻辑层”与“视图展示层”的桥梁。

4.1 DispathcerServlet的doDispatch方法

在入口处找到要执行的HandlerAdapter，调用handle方法继续

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception { HttpServletRequest processedRequest = request; HandlerExecutionChain mappedHandler = null; boolean multipartRequestParsed = false; WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request); try { ModelAndView mv = null; Exception dispatchException = null; try { processedRequest = checkMultipart(request); multipartRequestParsed = (processedRequest != request); // Determine handler for the current request. // 找到执行链,根据请求路径匹配到controller的方法 mappedHandler = getHandler(processedRequest); if (mappedHandler == null) { noHandlerFound(processedRequest, response); return; } // Determine handler adapter for the current request. // 找到对应的HandlerAdapter,执行链中的handler类型为HandlerMethod的. HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler()); // Process last-modified header, if supported by the handler. String method = request.getMethod(); boolean isGet = HttpMethod.GET.matches(method); if (isGet || HttpMethod.HEAD.matches(method)) { long lastModified = ha.getLastModified(request, mappedHandler.getHandler()); if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) { return; } } if (!mappedHandler.applyPreHandle(processedRequest, response)) { return; } // Actually invoke the handler. 真正进行处理的地方 mv = ha.handle(processedRequest, response, mappedHandler.getHandler()); if (asyncManager.isConcurrentHandlingStarted()) { return; } applyDefaultViewName(processedRequest, mv); mappedHandler.applyPostHandle(processedRequest, response, mv); .......... } 

4.2 RequestmappingHanderApapter对@initBInder注解缓存方法进行处理

找到对应的handlerAdapter后进入invokeHandlerMethod()方法,在这里通过构建WebDataBinderFactory对initBinder注解进行构建，供后续使用，具体逻辑如下。
通过getDataBinderFactory()方法从之前缓存的Map> initBinderAdviceCache中生成binderFactory

@Nullable protected ModelAndView invokeHandlerMethod(HttpServletRequest request, HttpServletResponse response, HandlerMethod handlerMethod) throws Exception { ServletWebRequest webRequest = new ServletWebRequest(request, response); try { //根据initBinder注解,获取对应的factory，主要成员是InvocableHandlerMethod，就包括之前缓存的。 WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod); ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory); // 创建可调用的对象，进行调用逻辑处理 ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod); if (this.argumentResolvers != null) { invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers); } if (this.returnValueHandlers != null) { invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers); } // binderFactory设置进invocableMethod， invocableMethod.setDataBinderFactory(binderFactory); invocableMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer); ModelAndViewContainer mavContainer = new ModelAndViewContainer(); mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request)); modelFactory.initModel(webRequest, mavContainer, invocableMethod); mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect); AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response); asyncWebRequest.setTimeout(this.asyncRequestTimeout); WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request); asyncManager.setTaskExecutor(this.taskExecutor); asyncManager.setAsyncWebRequest(asyncWebRequest); asyncManager.registerCallableInterceptors(this.callableInterceptors); asyncManager.registerDeferredResultInterceptors(this.deferredResultInterceptors); if (asyncManager.hasConcurrentResult()) { Object result = asyncManager.getConcurrentResult(); mavContainer = (ModelAndViewContainer) asyncManager.getConcurrentResultContext()[0]; asyncManager.clearConcurrentResult(); LogFormatUtils.traceDebug(logger, traceOn -> { String formatted = LogFormatUtils.formatValue(result, !traceOn); return "Resume with async result [" + formatted + "]"; }); invocableMethod = invocableMethod.wrapConcurrentResult(result); } // 继续进行处理 invocableMethod.invokeAndHandle(webRequest, mavContainer); if (asyncManager.isConcurrentHandlingStarted()) { return null; } return getModelAndView(mavContainer, modelFactory, webRequest); } finally { webRequest.requestCompleted(); } } // 生成WebDataBinderFactory的具体逻辑 private WebDataBinderFactory getDataBinderFactory(HandlerMethod handlerMethod) throws Exception { Class<?> handlerType = handlerMethod.getBeanType(); Set<Method> methods = this.initBinderCache.get(handlerType); if (methods == null) { methods = MethodIntrospector.selectMethods(handlerType, INIT_BINDER_METHODS); this.initBinderCache.put(handlerType, methods); } List<InvocableHandlerMethod> initBinderMethods = new ArrayList<>(); // Global methods first 获取之前项目启动缓存的initMethod this.initBinderAdviceCache.forEach((controllerAdviceBean, methodSet) -> { if (controllerAdviceBean.isApplicableToBeanType(handlerType)) { Object bean = controllerAdviceBean.resolveBean(); for (Method method : methodSet) { initBinderMethods.add(createInitBinderMethod(bean, method)); } } }); for (Method method : methods) { Object bean = handlerMethod.getBean(); initBinderMethods.add(createInitBinderMethod(bean, method)); } return createDataBinderFactory(initBinderMethods); } 

经过上面的处理，发现initBinder标注的注解方法已经成功缓存进bindFactory。

4.3 继续调用getMethodArgumentValues进行后续处理

继续往下跟踪，进入InvocableHandlerMethod的invokeForRequest方法，里面有getMethodArgumentValues方法，会对请求参数进行处理。
最终使用AbstractNamedValueMethodArgumentResolver的resolveArgument（）方法对请求字符串格式数据进行处理

// 请求Controller方法如下 public ResponseData<IPage<CompanyVo>> listCompany(HttpServletRequest servletRequest, @RequestBody CompanySearch companySearch, @RequestParam LocalDate localDate){ getLoginUser(servletRequest); return ResponseData.success(companyService.listCompany(companySearch)); } protected Object[] getMethodArgumentValues(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer, Object... providedArgs) throws Exception { // 得到方法的参数列表 MethodParameter[] parameters = getMethodParameters(); if (ObjectUtils.isEmpty(parameters)) { return EMPTY_ARGS; } Object[] args = new Object[parameters.length]; // 循环如处理请求参数 for (int i = 0; i < parameters.length; i++) { MethodParameter parameter = parameters[i]; parameter.initParameterNameDiscovery(this.parameterNameDiscoverer); args[i] = findProvidedArgument(parameter, providedArgs); if (args[i] != null) { continue; } if (!this.resolvers.supportsParameter(parameter)) { throw new IllegalStateException(formatArgumentError(parameter, "No suitable resolver")); } try { // 真正进行参数处理的地方 args[i] = this.resolvers.resolveArgument(parameter, mavContainer, request, this.dataBinderFactory); } catch (Exception ex) { // Leave stack trace for later, exception may actually be resolved and handled... if (logger.isDebugEnabled()) { String exMsg = ex.getMessage(); if (exMsg != null && !exMsg.contains(parameter.getExecutable().toGenericString())) { logger.debug(formatArgumentError(parameter, exMsg)); } } throw ex; } } return args; } // 最终会使用AbstractNamedValueMethodArgumentResolver来进行处理 public final Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer, NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception { NamedValueInfo namedValueInfo = getNamedValueInfo(parameter); MethodParameter nestedParameter = parameter.nestedIfOptional(); // 得到请求参数名称为"localdate" Object resolvedName = resolveEmbeddedValuesAndExpressions(namedValueInfo.name); if (resolvedName == null) { throw new IllegalArgumentException( "Specified name must not resolve to null: [" + namedValueInfo.name + "]"); } // 获取请求的locadate的值，此时为字符串格式"yyyy-mm-dd" Object arg = resolveName(resolvedName.toString(), nestedParameter, webRequest); if (arg == null) { if (namedValueInfo.defaultValue != null) { arg = resolveEmbeddedValuesAndExpressions(namedValueInfo.defaultValue); } else if (namedValueInfo.required && !nestedParameter.isOptional()) { handleMissingValue(namedValueInfo.name, nestedParameter, webRequest); } arg = handleNullValue(namedValueInfo.name, arg, nestedParameter.getNestedParameterType()); } else if ("".equals(arg) && namedValueInfo.defaultValue != null) { arg = resolveEmbeddedValuesAndExpressions(namedValueInfo.defaultValue); } // 这里就会使用bindFactory进行处理 if (binderFactory != null) { WebDataBinder binder = binderFactory.createBinder(webRequest, null, namedValueInfo.name); try { // 经过这里进行处理，输入的string类型就会转为LocalDate了 arg = binder.convertIfNecessary(arg, parameter.getParameterType(), parameter); } catch (ConversionNotSupportedException ex) { throw new MethodArgumentConversionNotSupportedException(arg, ex.getRequiredType(), namedValueInfo.name, parameter, ex.getCause()); } catch (TypeMismatchException ex) { throw new MethodArgumentTypeMismatchException(arg, ex.getRequiredType(), namedValueInfo.name, parameter, ex.getCause()); } // Check for null value after conversion of incoming argument value if (arg == null && namedValueInfo.defaultValue == null && namedValueInfo.required && !nestedParameter.isOptional()) { handleMissingValueAfterConversion(namedValueInfo.name, nestedParameter, webRequest); } } handleResolvedValue(arg, namedValueInfo.name, parameter, mavContainer, webRequest); return arg; } 

最后附上上面调用过程中一些类的介绍

以上就是ControllerAdivce的全介绍。通过对源码的学习，加深了对HTTP请求过程的理解。

参考:https://blog.csdn.net/zmm__1377445292/article/details/116158554

作者：京东物流 付鹏嘎

来源：京东云开发者社区 自猿其说Tech