Spring 在3.2版本后面增加了一个ControllerAdvice注解。网上的资料说的都是ControllerAdvice配合ExceptionHandler注解可以统一处理异常。而Spring MVC是如何做到的资料却比较少，下面会先给出使用的例子和踩过的一个坑。然后进行相应的源码分析，之后再介始ControllerAdvice另外的两种使用方式。
ControllerAdvice的简单使用
- ControllerAdvice配合ExceptionHandler可以统一处理系统的异常，我们先定义一个ExceptionAdvice类用于处理系统的两种类型的异常。代码如下：
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.ResponseBody;
import com.pptv.frame.dto.common.ResponseDTO;
import com.pptv.frame.dto.common.ServiceCodeEnum;
@ControllerAdvice
public class ExceptionAdvice {
@ExceptionHandler({
ArrayIndexOutOfBoundsException.class
})
@ResponseBody
public ResponseDTO handleArrayIndexOutOfBoundsException(ArrayIndexOutOfBoundsException e) {
// TODO 记录log日志
e.printStackTrace();
ResponseDTO responseDTO = new ResponseDTO();
responseDTO.wrapResponse(ServiceCodeEnum.E999998, "数组越界异常");
return responseDTO;
}
@ExceptionHandler({
Exception.class
})
@ResponseBody
public ResponseDTO handleException(Exception e) {
// TODO 记录log日志
e.printStackTrace();
ResponseDTO responseDTO = new ResponseDTO();
responseDTO.wrapResponse(ServiceCodeEnum.E999998, "未知异常");
return responseDTO;
}
}
- Spring mvc 的配置如下(这里用到了mvc:annotation-driven)：
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:cxf="http://cxf.apache.org/core"
xmlns:p="http://cxf.apache.org/policy" xmlns:ss="http://www.springframework.org/schema/security"
xmlns:jaxws="http://cxf.apache.org/jaxws" xmlns:jee="http://www.springframework.org/schema/jee"
xmlns:aop="http://www.springframework.org/schema/aop" xmlns:tx="http://www.springframework.org/schema/tx"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:mvc="http://www.springframework.org/schema/mvc"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
http://cxf.apache.org/core http://cxf.apache.org/schemas/core.xsd
http://cxf.apache.org/jaxws http://cxf.apache.org/schemas/jaxws.xsd
http://cxf.apache.org/policy http://cxf.apache.org/schemas/policy.xsd
http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsd
http://www.springframework.org/schema/jee http://www.springframework.org/schema/jee/spring-jee.xsd
http://cxf.apache.org/bindings/soap http://cxf.apache.org/schemas/configuration/soap.xsd
http://www.springframework.org/schema/security http://www.springframework.org/schema/security/spring-security.xsd
http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd
http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd
http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx.xsd">
<context:component-scan
base-package="frame.web.controller;frame.web.advice" />
<!--===================== view resovler ===================== -->
<bean id="jstlViewResolver"
class="org.springframework.web.servlet.view.UrlBasedViewResolver">
<property name="order" value="1" />
<property name="viewClass"
value="org.springframework.web.servlet.view.JstlView" />
<property name="prefix" value="/WEB-INF/jsp/" />
</bean>
<!-- 配置Fastjson支持 -->
<mvc:annotation-driven conversion-service="conversionService">
<mvc:message-converters register-defaults="true">
<bean
class="com.alibaba.fastjson.support.spring.FastJsonHttpMessageConverter">
<property name="supportedMediaTypes" value="text/html;charset=UTF-8" />
<property name="features">
<array>
<value>WriteMapNullValue</value>
<value>WriteNullStringAsEmpty</value>
</array>
</property>
</bean>
</mvc:message-converters>
</mvc:annotation-driven>
<!-- 自定义参数转换 -->
<bean id="conversionService"
class="org.springframework.format.support.FormattingConversionServiceFactoryBean">
</bean>
</beans>
遇到的一个坑是当spring mvc配置文件不用<mvc:annotation-drive>这个标签而是手动将RequestMappingHandlerMapping与RequestMappingHandlerAdapter这两个类让spring容器管理，上面的ControllerAdvice将不起作用
<bean
class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping" />
<bean
class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter">
<property name="webBindingInitializer">
<bean
class="org.springframework.web.bind.support.ConfigurableWebBindingInitializer">
<property name="conversionService" ref="conversionService" />
</bean>
</property>
<property name="messageConverters">
<list>
<ref bean="mappingJackson2HttpMessageConverter" />
<ref bean="stringHttpMessageConverter" />
</list>
</property>
</bean>
Spring MVC是如何处理异常的
下面来看看Spring MVC是如何处理异常的，为什么我手动配置了RequestMappingHandlerMapping和RequestMappingHandlerAdapter ControllerAdvice就不会对异常进行拦截呢而通过<mvc:annotation-drive>这个标签就可以呢？我们从Spring MVC的入口看一下异常是如何处理的。下面是关键代码（关键代码都有相应的注释）：
public class DispatcherServlet extends FrameworkServlet {
/**
*这个方法是Spring MVC的入口方法，可以看到Spring MVC人具体处理流程
**/
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;
//这里有个try，下面的catch就是用于处理异常的
try {
//检查是否是上传文件的请求
processedRequest = checkMultipart(request);
multipartRequestParsed = (processedRequest != request);
// Determine handler for the current request.
//根据请求的request得到HandlerExecutionChain 对象，里面有Inceptor和相应的Controller
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null || mappedHandler.getHandler() == null) {
noHandlerFound(processedRequest, response);
return;
}
// Determine handler adapter for the current request.
//根据配置的HandlerAdapter 对handler进行适配
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
// Process last-modified header, if supported by the handler.
String method = request.getMethod();
boolean isGet = "GET".equals(method);
if (isGet || "HEAD".equals(method)) {
long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
if (logger.isDebugEnabled()) {
logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);
}
if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
return;
}
}
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
// Actually invoke the handler.
//这里会调用具体的Handler也就是我们写的Controller
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
applyDefaultViewName(processedRequest, mv);
mappedHandler.applyPostHandle(processedRequest, response, mv);
}
catch (Exception ex) {
//上面处理的逻辑有任何的异常，都将会落到这里，用dispatchException 这个变量接住异常引用
dispatchException = ex;
}
catch (Throwable err) {
//如果抛的是error， 这里也会把异常给接住
// As of 4.3, we're processing Errors thrown from handler methods as well,
// making them available for @ExceptionHandler methods and other scenarios.
dispatchException = new NestedServletException("Handler dispatch failed", err);
}
//具体处理异常的逻辑看来是在这个方法里了，具体的逻辑看下面的源码
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
}
catch (Exception ex) {
//这是最外面的try，这里需要处理Inteceptor里After的逻辑
triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
}
catch (Throwable err) {
//这是最外面的try，这里需要处理Inteceptor里After的逻辑
triggerAfterCompletion(processedRequest, response, mappedHandler,
new NestedServletException("Handler processing failed", err));
}
finally {
if (asyncManager.isConcurrentHandlingStarted()) {
// Instead of postHandle and afterCompletion
if (mappedHandler != null) {
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
}
}
else {
// Clean up any resources used by a multipart request.
if (multipartRequestParsed) {
cleanupMultipart(processedRequest);
}
}
}
}
/**
*这个方法里processHandlerException用于处理各种不同的Exception
**/
private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
HandlerExecutionChain mappedHandler, ModelAndView mv, Exception exception) throws Exception {
boolean errorView = false;
//当controller抛出异常后，就会执行下面的逻辑啦
if (exception != null) {
if (exception instanceof ModelAndViewDefiningException) {
logger.debug("ModelAndViewDefiningException encountered", exception);
mv = ((ModelAndViewDefiningException) exception).getModelAndView();
}
else {
//各种不同的异常会走到这里来处理，processHandlerException的源码在下面有详细的注释
Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
mv = processHandlerException(request, response, handler, exception);
errorView = (mv != null);
}
}
// Did the handler return a view to render?
if (mv != null && !mv.wasCleared()) {
render(mv, request, response);
if (errorView) {
WebUtils.clearErrorRequestAttributes(request);
}
}
else {
if (logger.isDebugEnabled()) {
logger.debug("Null ModelAndView returned to DispatcherServlet with name '" + getServletName() +
"': assuming HandlerAdapter completed request handling");
}
}
if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
// Concurrent handling started during a forward
return;
}
if (mappedHandler != null) {
mappedHandler.triggerAfterCompletion(request, response, null);
}
}
/**
**这里是用于处理Spring MVC异常的入口
**/
protected ModelAndView processHandlerException(HttpServletRequest request, HttpServletResponse response,
Object handler, Exception ex) throws Exception {
// Check registered HandlerExceptionResolvers...
//通过注入的handlerExceptionResolvers来处得具体的Exception，这也就找到了我上面踩坑的原因了。
ModelAndView exMv = null;
for (HandlerExceptionResolver handlerExceptionResolver : this.handlerExceptionResolvers) {
exMv = handlerExceptionResolver.resolveException(request, response, handler, ex);
if (exMv != null) {
break;
}
}
if (exMv != null) {
if (exMv.isEmpty()) {
request.setAttribute(EXCEPTION_ATTRIBUTE, ex);
return null;
}
// We might still need view name translation for a plain error model...
if (!exMv.hasView()) {
exMv.setViewName(getDefaultViewName(request));
}
if (logger.isDebugEnabled()) {
logger.debug("Handler execution resulted in exception - forwarding to resolved error view: " + exMv, ex);
}
WebUtils.exposeErrorRequestAttributes(request, ex, getServletName());
return exMv;
}
throw ex;
}
}
通过上面的源码，我们一步步可以跟踪到processHandlerException这个方法，这个方法里通过HandlerExceptionResolver 来处理具体的异常，而当我们手动只配置RequestMappingHandlerMapping和RequestMappingHandlerAdapter时，并没有配置任何的HandlerExceptionResolver 。也就是为什么ControllerAdvice不会对异常进行处理了，我们同时也可以想到<mvc:annotation-drive>一定是帮助我们注入了一个HandlerExceptionResolver 类。下面我们通过分析AnnotationDrivenBeanDefinitionParser这个类来看看到底给我们注入的是那个HandlerExceptionResolver，AnnotationDrivenBeanDefinitionParser类就是用于解析<mvc:annotation-drive>标签的。下面是AnnotationDrivenBeanDefinitionParser的部分源码：
package org.springframework.web.servlet.config;
class AnnotationDrivenBeanDefinitionParser implements BeanDefinitionParser {
/**
*parse是这个类的核心方法，它用于解析 annotation-drive标签里的内容，根据标签里的内容往spring ioc容器里注入具体的对象。
**/
@Override
public BeanDefinition parse(Element element, ParserContext parserContext) {
Object source = parserContext.extractSource(element);
XmlReaderContext readerContext = parserContext.getReaderContext();
CompositeComponentDefinition compDefinition = new CompositeComponentDefinition(element.getTagName(), source);
parserContext.pushContainingComponent(compDefinition);
RuntimeBeanReference contentNegotiationManager = getContentNegotiationManager(element, source, parserContext);
//这里有我们熟悉的RequestMappingHandlerMapping，
RootBeanDefinition handlerMappingDef = new RootBeanDefinition(RequestMappingHandlerMapping.class);
handlerMappingDef.setSource(source);
handlerMappingDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
handlerMappingDef.getPropertyValues().add("order", 0);
handlerMappingDef.getPropertyValues().add("contentNegotiationManager", contentNegotiationManager);
if (element.hasAttribute("enable-matrix-variables")) {
Boolean enableMatrixVariables = Boolean.valueOf(element.getAttribute("enable-matrix-variables"));
handlerMappingDef.getPropertyValues().add("removeSemicolonContent", !enableMatrixVariables);
}
else if (element.hasAttribute("enableMatrixVariables")) {
Boolean enableMatrixVariables = Boolean.valueOf(element.getAttribute("enableMatrixVariables"));
handlerMappingDef.getPropertyValues().add("removeSemicolonContent", !enableMatrixVariables);
}
configurePathMatchingProperties(handlerMappingDef, element, parserContext);
readerContext.getRegistry().registerBeanDefinition(HANDLER_MAPPING_BEAN_NAME , handlerMappingDef);
RuntimeBeanReference corsConfigurationsRef = MvcNamespaceUtils.registerCorsConfigurations(null, parserContext, source);
handlerMappingDef.getPropertyValues().add("corsConfigurations", corsConfigurationsRef);
//这里会注入具体的ConversionService用于将json,xml转成Spring mvc里的请求和返回对象
RuntimeBeanReference conversionService = getConversionService(element, source, parserContext);
RuntimeBeanReference validator = getValidator(element, source, parserContext);
RuntimeBeanReference messageCodesResolver = getMessageCodesResolver(element);
RootBeanDefinition bindingDef = new RootBeanDefinition(ConfigurableWebBindingInitializer.class);
bindingDef.setSource(source);
bindingDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
bindingDef.getPropertyValues().add("conversionService", conversionService);
bindingDef.getPropertyValues().add("validator", validator);
bindingDef.getPropertyValues().add("messageCodesResolver", messageCodesResolver);
ManagedList<?> messageConverters = getMessageConverters(element, source, parserContext);
ManagedList<?> argumentResolvers = getArgumentResolvers(element, parserContext);
ManagedList<?> returnValueHandlers = getReturnValueHandlers(element, parserContext);
String asyncTimeout = getAsyncTimeout(element);
RuntimeBeanReference asyncExecutor = getAsyncExecutor(element);
ManagedList<?> callableInterceptors = getCallableInterceptors(element, source, parserContext);
ManagedList<?> deferredResultInterceptors = getDeferredResultInterceptors(element, source, parserContext);
//RequestMappingHandlerAdapter也会在这里注入
RootBeanDefinition handlerAdapterDef = new RootBeanDefinition(RequestMappingHandlerAdapter.class);
handlerAdapterDef.setSource(source);
handlerAdapterDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
handlerAdapterDef.getPropertyValues().add("contentNegotiationManager", contentNegotiationManager);
handlerAdapterDef.getPropertyValues().add("webBindingInitializer", bindingDef);
handlerAdapterDef.getPropertyValues().add("messageConverters", messageConverters);
addRequestBodyAdvice(handlerAdapterDef);
addResponseBodyAdvice(handlerAdapterDef);
if (element.hasAttribute("ignore-default-model-on-redirect")) {
Boolean ignoreDefaultModel = Boolean.valueOf(element.getAttribute("ignore-default-model-on-redirect"));
handlerAdapterDef.getPropertyValues().add("ignoreDefaultModelOnRedirect", ignoreDefaultModel);
}
else if (element.hasAttribute("ignoreDefaultModelOnRedirect")) {
// "ignoreDefaultModelOnRedirect" spelling is deprecated
Boolean ignoreDefaultModel = Boolean.valueOf(element.getAttribute("ignoreDefaultModelOnRedirect"));
handlerAdapterDef.getPropertyValues().add("ignoreDefaultModelOnRedirect", ignoreDefaultModel);
}
if (argumentResolvers != null) {
handlerAdapterDef.getPropertyValues().add("customArgumentResolvers", argumentResolvers);
}
if (returnValueHandlers != null) {
handlerAdapterDef.getPropertyValues().add("customReturnValueHandlers", returnValueHandlers);
}
if (asyncTimeout != null) {
handlerAdapterDef.getPropertyValues().add("asyncRequestTimeout", asyncTimeout);
}
if (asyncExecutor != null) {
handlerAdapterDef.getPropertyValues().add("taskExecutor", asyncExecutor);
}
handlerAdapterDef.getPropertyValues().add("callableInterceptors", callableInterceptors);
handlerAdapterDef.getPropertyValues().add("deferredResultInterceptors", deferredResultInterceptors);
readerContext.getRegistry().registerBeanDefinition(HANDLER_ADAPTER_BEAN_NAME , handlerAdapterDef);
String uriCompContribName = MvcUriComponentsBuilder.MVC_URI_COMPONENTS_CONTRIBUTOR_BEAN_NAME;
RootBeanDefinition uriCompContribDef = new RootBeanDefinition(CompositeUriComponentsContributorFactoryBean.class);
uriCompContribDef.setSource(source);
uriCompContribDef.getPropertyValues().addPropertyValue("handlerAdapter", handlerAdapterDef);
uriCompContribDef.getPropertyValues().addPropertyValue("conversionService", conversionService);
readerContext.getRegistry().registerBeanDefinition(uriCompContribName, uriCompContribDef);
RootBeanDefinition csInterceptorDef = new RootBeanDefinition(ConversionServiceExposingInterceptor.class);
csInterceptorDef.setSource(source);
csInterceptorDef.getConstructorArgumentValues().addIndexedArgumentValue(0, conversionService);
RootBeanDefinition mappedCsInterceptorDef = new RootBeanDefinition(MappedInterceptor.class);
mappedCsInterceptorDef.setSource(source);
mappedCsInterceptorDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
mappedCsInterceptorDef.getConstructorArgumentValues().addIndexedArgumentValue(0, (Object) null);
mappedCsInterceptorDef.getConstructorArgumentValues().addIndexedArgumentValue(1, csInterceptorDef);
String mappedInterceptorName = readerContext.registerWithGeneratedName(mappedCsInterceptorDef);
//这里有我们需要找的ExceptionHandlerExceptionResolver，
RootBeanDefinition exceptionHandlerExceptionResolver = new RootBeanDefinition(ExceptionHandlerExceptionResolver.class);
exceptionHandlerExceptionResolver.setSource(source);
exceptionHandlerExceptionResolver.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
exceptionHandlerExceptionResolver.getPropertyValues().add("contentNegotiationManager", contentNegotiationManager);
exceptionHandlerExceptionResolver.getPropertyValues().add("messageConverters", messageConverters);
exceptionHandlerExceptionResolver.getPropertyValues().add("order", 0);
addResponseBodyAdvice(exceptionHandlerExceptionResolver);
if (argumentResolvers != null) {
exceptionHandlerExceptionResolver.getPropertyValues().add("customArgumentResolvers", argumentResolvers);
}
if (returnValueHandlers != null) {
exceptionHandlerExceptionResolver.getPropertyValues().add("customReturnValueHandlers", returnValueHandlers);
}
String methodExceptionResolverName = readerContext.registerWithGeneratedName(exceptionHandlerExceptionResolver);
RootBeanDefinition responseStatusExceptionResolver = new RootBeanDefinition(ResponseStatusExceptionResolver.class);
responseStatusExceptionResolver.setSource(source);
responseStatusExceptionResolver.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
responseStatusExceptionResolver.getPropertyValues().add("order", 1);
String responseStatusExceptionResolverName =
readerContext.registerWithGeneratedName(responseStatusExceptionResolver);
RootBeanDefinition defaultExceptionResolver = new RootBeanDefinition(DefaultHandlerExceptionResolver.class);
defaultExceptionResolver.setSource(source);
defaultExceptionResolver.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
defaultExceptionResolver.getPropertyValues().add("order", 2);
String defaultExceptionResolverName =
readerContext.registerWithGeneratedName(defaultExceptionResolver);
parserContext.registerComponent(new BeanComponentDefinition(handlerMappingDef, HANDLER_MAPPING_BEAN_NAME));
parserContext.registerComponent(new BeanComponentDefinition(handlerAdapterDef, HANDLER_ADAPTER_BEAN_NAME));
parserContext.registerComponent(new BeanComponentDefinition(uriCompContribDef, uriCompContribName));
parserContext.registerComponent(new BeanComponentDefinition(exceptionHandlerExceptionResolver, methodExceptionResolverName));
parserContext.registerComponent(new BeanComponentDefinition(responseStatusExceptionResolver, responseStatusExceptionResolverName));
parserContext.registerComponent(new BeanComponentDefinition(defaultExceptionResolver, defaultExceptionResolverName));
parserContext.registerComponent(new BeanComponentDefinition(mappedCsInterceptorDef, mappedInterceptorName));
// Ensure BeanNameUrlHandlerMapping (SPR-8289) and default HandlerAdapters are not "turned off"
MvcNamespaceUtils.registerDefaultComponents(parserContext, source);
parserContext.popAndRegisterContainingComponent();
return null;
}
}
通过上面代码的分析， 我们可以找到ExceptionHandlerExceptionResolver这个类来用于处理Spring MVC的各种异常，那ExceptionHandlerExceptionResolver具体又是如何跟ControllerAdvice配合使用来处理各种异常的呢?我们来看看ExceptionHandlerExceptionResolver里的关键代码：
package org.springframework.web.servlet.mvc.method.annotation;
public class ExceptionHandlerExceptionResolver extends AbstractHandlerMethodExceptionResolver
implements ApplicationContextAware, InitializingBean {
//这里有个map用于保存ControllerAdviceBean
private final Map<ControllerAdviceBean, ExceptionHandlerMethodResolver> exceptionHandlerAdviceCache =
new LinkedHashMap<ControllerAdviceBean, ExceptionHandlerMethodResolver>();
//这个方法是由spring 容器调用的
@Override
public void afterPropertiesSet() {
// Do this first, it may add ResponseBodyAdvice beans
//这个方法里会处理ExceptionHandler
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);
}
}
/**
*这个方法里会在spring ioc容器里找出标注了@ControllerAdvice的类，如果有方法标注了@ExceptionHandler会生成一个ExceptionHandlerMethodResolver类用于处理异常并放到exceptionHandlerAdviceCache这个map缓存类里。
**/
private void initExceptionHandlerAdviceCache() {
if (getApplicationContext() == null) {
return;
}
if (logger.isDebugEnabled()) {
logger.debug("Looking for exception mappings: " + getApplicationContext());
}
//这里会找到容器里标注了ControllerAdvice标签的类
List<ControllerAdviceBean> adviceBeans = ControllerAdviceBean.findAnnotatedBeans(getApplicationContext());
AnnotationAwareOrderComparator.sort(adviceBeans);
for (ControllerAdviceBean adviceBean : adviceBeans) {
//这个构造方法里会检查ControllerAdvice类里是否有@ExceptionHandler标注的方法，在ExceptionHandlerMethodResolver 有个异常的map。
ExceptionHandlerMethodResolver resolver = new ExceptionHandlerMethodResolver(adviceBean.getBeanType());
if (resolver.hasExceptionMappings()) {
//如果有@ExceptionHandler方法，会执行下面的逻辑
this.exceptionHandlerAdviceCache.put(adviceBean, resolver);
if (logger.isInfoEnabled()) {
logger.info("Detected @ExceptionHandler methods in " + adviceBean);
}
}
if (ResponseBodyAdvice.class.isAssignableFrom(adviceBean.getBeanType())) {
this.responseBodyAdvice.add(adviceBean);
if (logger.isInfoEnabled()) {
logger.info("Detected ResponseBodyAdvice implementation in " + adviceBean);
}
}
}
}
/**
** 这个方法会根据exceptionHandlerAdviceCache这个找到具体需要处理异常的方法
*/
protected ServletInvocableHandlerMethod getExceptionHandlerMethod(HandlerMethod handlerMethod, Exception exception) {
Class<?> handlerType = (handlerMethod != null ? handlerMethod.getBeanType() : null);
if (handlerMethod != null) {
ExceptionHandlerMethodResolver resolver = this.exceptionHandlerCache.get(handlerType);
if (resolver == null) {
resolver = new ExceptionHandlerMethodResolver(handlerType);
this.exceptionHandlerCache.put(handlerType, resolver);
}
Method method = resolver.resolveMethod(exception);
if (method != null) {
return new ServletInvocableHandlerMethod(handlerMethod.getBean(), method);
}
}
for (Entry<ControllerAdviceBean, ExceptionHandlerMethodResolver> entry : this.exceptionHandlerAdviceCache.entrySet()) {
if (entry.getKey().isApplicableToBeanType(handlerType)) {
ExceptionHandlerMethodResolver resolver = entry.getValue();
//根据具体的异常找到处理异常的方法，然后调用
Method method = resolver.resolveMethod(exception);
if (method != null) {
return new ServletInvocableHandlerMethod(entry.getKey().resolveBean(), method);
}
}
}
return null;
}
}
ExceptionHandlerExceptionResolver这个类首先会扫描容器里所有的ControllerAdvice,如果ControllerAdvice标注了@ExceptionHandler会加到一个map缓存里。在处理具体的异常的时候，会去这个缓存里一个个找是否有ControllerAdvice能够处理这个异常。整个流程我们就分析到这里，下面看看ControllerAdvice的另外两个用法。
RequestBodyAdvice与ResponseBodyAdvice
Spring在4.2的版本给我们提供了RequestBodyAdvice与ResponseBodyAdvice这两个接口，而ControllerAdvice是在3.2这个版本里的。那RequestBodyAdvice和ResponseBodyAdvice能够帮我们做些什么事性呢？假如现在有个需求，正常接口返回的是json，但传入的请求头里有callback参数需要返回jsonp格式的数据需要如何做呢？下面我们来看看RequestBodyAdvice和ResponseBodyAdvice这两个类的具体定义，RequestBodyAdvice代码如下：
package org.springframework.web.servlet.mvc.method.annotation;
import java.io.IOException;
import java.lang.reflect.Type;
import org.springframework.core.MethodParameter;
import org.springframework.http.HttpInputMessage;
import org.springframework.http.converter.HttpMessageConverter;
public interface RequestBodyAdvice {
//supports方法用于决定是否调用下面的方法，
boolean supports(MethodParameter methodParameter, Type targetType,
Class<? extends HttpMessageConverter<?>> converterType);
//处理空参数据情况
Object handleEmptyBody(Object body, HttpInputMessage inputMessage, MethodParameter parameter,
Type targetType, Class<? extends HttpMessageConverter<?>> converterType);
//在参数读取之前处理的逻辑
HttpInputMessage beforeBodyRead(HttpInputMessage inputMessage, MethodParameter parameter,
Type targetType, Class<? extends HttpMessageConverter<?>> converterType) throws IOException;
//在参数读取之后处理的逻辑
Object afterBodyRead(Object body, HttpInputMessage inputMessage, MethodParameter parameter,
Type targetType, Class<? extends HttpMessageConverter<?>> converterType);
}
从RequestBodyAdvice的定义我们可以清楚的看出他主要用于处理Spring MVC请求参数相关的逻辑，首先定义了support方法用于判断是否能够对请求参数做进一步的处理，然后定义了在读取参数前后方法分别用于处理请求参数。这里的读取前后是在Spring MVC调用了HttpMessageConverter对参数进行了转义，所以使用起来还是很方便的。下面来看看ResponseBodyAdvice的定义：
package org.springframework.web.servlet.mvc.method.annotation;
import org.springframework.core.MethodParameter;
import org.springframework.http.MediaType;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.http.server.ServerHttpRequest;
import org.springframework.http.server.ServerHttpResponse;
public interface ResponseBodyAdvice<T> {
//这个方法用于判断是否需要调用beforeBodyWrite方法
boolean supports(MethodParameter returnType, Class<? extends HttpMessageConverter<?>> converterType);
//这里在写入的时候就可以修改要写入的值啦
T beforeBodyWrite(T body, MethodParameter returnType, MediaType selectedContentType,
Class<? extends HttpMessageConverter<?>> selectedConverterType,
ServerHttpRequest request, ServerHttpResponse response);
}
ResponseBodyAdvice用于对写入的数据进行修改，通过ResponseBodyAdvice我们可以很方便的将json数据改成jsonp进行返回。下面我自定义了一个JsonpAdvice用于处理根据header参数返回jsonp格式的数据。代码如下：
import javax.servlet.http.HttpServletRequest;
import org.apache.commons.lang3.StringUtils;
import org.springframework.core.MethodParameter;
import org.springframework.http.MediaType;
import org.springframework.http.converter.json.MappingJacksonValue;
import org.springframework.http.server.ServerHttpRequest;
import org.springframework.http.server.ServerHttpResponse;
import org.springframework.http.server.ServletServerHttpRequest;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.servlet.mvc.method.annotation.AbstractMappingJacksonResponseBodyAdvice;
/**
* 处理需要返回jsonp的Advice 功能描述:
*
* @version 2.0.0
* @author zhiminchen
*/
@ControllerAdvice
public class JsonpAdvice extends AbstractMappingJacksonResponseBodyAdvice {
@Override
protected void beforeBodyWriteInternal(MappingJacksonValue bodyContainer,
MediaType contentType,
MethodParameter returnType,
ServerHttpRequest request,
ServerHttpResponse response) {
HttpServletRequest servletRequest = ((ServletServerHttpRequest) request).getServletRequest();
// 根据 header是否有callback参数决定是否返回jsonp格式的数据
String callback = servletRequest.getHeader("callback");
if (StringUtils.isNotBlank(callback)) {
MediaType contentTypeToUse = getContentType(contentType, request, response);
response.getHeaders().setContentType(contentTypeToUse);
bodyContainer.setJsonpFunction(callback);
}
}
protected MediaType getContentType(MediaType contentType,
ServerHttpRequest request,
ServerHttpResponse response) {
return new MediaType("application", "javascript");
}
}
如果采用的是FastJsonHttpMessageConverter作为类型转换器。上面的JsonpAdvice 不起作用， 我们可以再自定义一个争对FastJsonHttpMessageConverter的Jsonp拦截器，代码如下：
import javax.servlet.http.HttpServletRequest;
import org.apache.commons.lang3.StringUtils;
import org.springframework.core.MethodParameter;
import org.springframework.http.MediaType;
import org.springframework.http.server.ServerHttpRequest;
import org.springframework.http.server.ServerHttpResponse;
import org.springframework.http.server.ServletServerHttpRequest;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.servlet.mvc.method.annotation.ResponseBodyAdvice;
import com.alibaba.fastjson.JSONPObject;
import com.pptv.frame.dto.common.ResponseDTO;
/**
* 处理需要返回jsonp的Advice 功能描述:
*
* @version 2.0.0
* @author zhiminchen
*/
@ControllerAdvice
public class JsonpAdvice implements ResponseBodyAdvice {
@Override
public boolean supports(MethodParameter returnType,
Class converterType) {
return returnType.getMethod().getReturnType().equals(ResponseDTO.class);
}
@Override
public Object beforeBodyWrite(Object body,
MethodParameter returnType,
MediaType selectedContentType,
Class selectedConverterType,
ServerHttpRequest request,
ServerHttpResponse response) {
HttpServletRequest servletRequest = ((ServletServerHttpRequest) request).getServletRequest();
String callback = servletRequest.getHeader("callback");
if (StringUtils.isNotBlank(callback)) {
MediaType contentTypeToUse = getContentType(request, response);
response.getHeaders().setContentType(contentTypeToUse);
JSONPObject jsonpObject = new JSONPObject(callback);
jsonpObject.addParameter(body);
return jsonpObject;
} else {
return body;
}
}
protected MediaType getContentType(ServerHttpRequest request,
ServerHttpResponse response) {
return new MediaType("application", "javascript");
}
}
总结：
- Spring MVC通过@ControllerAdvice配合@ExceptionHandler能够统一处理系统的异常信息。
- ControllerAdvice配合RequestBodyAdvice与ResponseBodyAdvice可以方便的对请求参数与返回值进行修改。
