@ControllerAdvice注解使用及原理探究

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,

@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。
@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。
@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  
@InitBinderprotected 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() {@Overridepublic 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() {@Overridepublic 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() {@Overridepublic 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adapterinitHandlerAdapters(context);
// 异常响应处理的resolverinitHandlerExceptionResolvers(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

@Overridepublic void afterPropertiesSet() {// Do this first, it may add ResponseBody advice beans
// 这里会添加ResponseBody advice beansinitControllerAdviceCache();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。

@Overridepublic void afterPropertiesSet() {// Do this first, it may add ResponseBodyAdvice beansinitExceptionHandlerAdviceCache();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：

    @Nullablepublic 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

@Nullableprotected 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initMethodthis.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 valueif (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