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。
@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。
@RestControllerAdvice@Slf4jpublicclass 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)publicResponseData<Void>bizException(BusinessException e){
log.error("业务异常记录",e);returnResponseData.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。
@RestControllerAdvice@Slf4jpublicclass 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(){@Overridepublicvoid setAsText(Stringtext)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(){@Overridepublicvoid setAsText(Stringtext)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(){@Overridepublicvoid setAsText(Stringtext)throws IllegalArgumentException {
setValue(LocalTime.parse(text,DateTimeFormatter.ofPattern(DEFAULT_TIME_FORMAT)));}
});}
}// controller进行参数绑定publicResponseData<List<WorkCalendarVo>>listWorkCalendar(@RequestParamLocalDatedate){}
// 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")publicUsersetLoginUser(HttpServletRequest request){returnLoginContextUtils.getLoginUser(request);}// 使用@PostMapping("/list")publicResponseData<IPage<EmployeeVo>>listEmployee(@ModelAttribute("loginUser")Useruser,@RequestBodyEmployeeSearch employeeSearch){returnResponseData.success(employeeService.listEmployee(user,employeeSearch));}
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。
publicclass 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);}// ......}
@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
@Overridepublicvoid 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}
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。
@Overridepublicvoid 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：
@NullablepublicMethod 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);}
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。
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;booleanmultipartRequestParsed=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();booleanisGet=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);..........}
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()){returnnull;}returngetModelAndView(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));}returncreateDataBinderFactory(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。
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publicResponseData<IPage<CompanyVo>>listCompany(HttpServletRequest servletRequest,@RequestBodyCompanySearch companySearch,@RequestParamLocalDate localDate){
getLoginUser(servletRequest);returnResponseData.success(companyService.listCompany(companySearch));}
protected Object[]getMethodArgumentValues(NativeWebRequest request,@NullableModelAndViewContainer mavContainer,Object...providedArgs)throws Exception {// 得到方法的参数列表MethodParameter[]parameters=getMethodParameters();if(ObjectUtils.isEmpty(parameters)){returnEMPTY_ARGS;}
Object[]args=new Object[parameters.length];// 循环如处理请求参数for(inti=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;}
}returnargs;}// 最终会使用AbstractNamedValueMethodArgumentResolver来进行处理publicfinal Object resolveArgument(MethodParameter parameter,@NullableModelAndViewContainer mavContainer,NativeWebRequest webRequest,@NullableWebDataBinderFactory 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);}elseif(namedValueInfo.required&&!nestedParameter.isOptional()){
handleMissingValue(namedValueInfo.name,nestedParameter,webRequest);}
arg=handleNullValue(namedValueInfo.name,arg,nestedParameter.getNestedParameterType());}elseif("".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);returnarg;}
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