SpringMvc之HandlerExceptionResolver

故事先从SpringMvc的dispatcherServlert开始

1.执行onRefresh时调用initStrategies

protected void onRefresh(ApplicationContext context) {
this.initStrategies(context);
}

2.执行initStrategies

protected void initStrategies(ApplicationContext context) {
this.initMultipartResolver(context);
this.initLocaleResolver(context);
this.initThemeResolver(context);
this.initHandlerMappings(context);
this.initHandlerAdapters(context);
this.initHandlerExceptionResolvers(context);
this.initRequestToViewNameTranslator(context);
this.initViewResolvers(context);
this.initFlashMapManager(context);
}

3.初始化异常处理器

private void initHandlerExceptionResolvers(ApplicationContext context) {
this.handlerExceptionResolvers = null;
if(this.detectAllHandlerExceptionResolvers) {
Map<String, HandlerExceptionResolver> matchingBeans = BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerExceptionResolver.class, true, false);
if(!matchingBeans.isEmpty()) {
this.handlerExceptionResolvers = new ArrayList(matchingBeans.values());
OrderComparator.sort(this.handlerExceptionResolvers);
}
} else {
try {
HandlerExceptionResolver her = (HandlerExceptionResolver)context.getBean("handlerExceptionResolver", HandlerExceptionResolver.class);
this.handlerExceptionResolvers = Collections.singletonList(her);
} catch (NoSuchBeanDefinitionException var3) {
;
}
}

if(this.handlerExceptionResolvers == null) {
this.handlerExceptionResolvers = this.getDefaultStrategies(context, HandlerExceptionResolver.class);
if(this.logger.isDebugEnabled()) {
this.logger.debug("No HandlerExceptionResolvers found in servlet '" + this.getServletName() + "': using default");
}
}

}

Controller是如何将异常交给HandlerExceptionResolver处理的

1.springMvc的核心,doDispatch

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
HttpServletRequest processedRequest = request;
HandlerExecutionChain mappedHandler = null;
boolean multipartRequestParsed = false;
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

try {
try {
ModelAndView mv = null;
Exception dispatchException = null;

try {
processedRequest = this.checkMultipart(request);
multipartRequestParsed = processedRequest != request;
mappedHandler = this.getHandler(processedRequest);
if(mappedHandler == null || mappedHandler.getHandler() == null) {
this.noHandlerFound(processedRequest, response);
return;
}

HandlerAdapter ha = this.getHandlerAdapter(mappedHandler.getHandler());
String method = request.getMethod();
boolean isGet = "GET".equals(method);
if(isGet || "HEAD".equals(method)) {
long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
if(this.logger.isDebugEnabled()) {
this.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;
}

mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
if(asyncManager.isConcurrentHandlingStarted()) {
return;
}

this.applyDefaultViewName(request, mv);
mappedHandler.applyPostHandle(processedRequest, response, mv);
} catch (Exception var19) {
dispatchException = var19;
}
________________________________________________________________________
执行Controller方法后调用processDispatchResult方法检测及处理异常
________________________________________________________________________

this.processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
} catch (Exception var20) {
this.triggerAfterCompletion(processedRequest, response, mappedHandler, var20);
} catch (Error var21) {
this.triggerAfterCompletionWithError(processedRequest, response, mappedHandler, var21);
}

} finally {
if(asyncManager.isConcurrentHandlingStarted()) {
if(mappedHandler != null) {
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
}
} else if(multipartRequestParsed) {
this.cleanupMultipart(processedRequest);
}

}
}

当发生异常后执行processDispatchResult

2.执行processDispatchResult

private void processDispatchResult(HttpServletRequest request, HttpServletResponse response, HandlerExecutionChain mappedHandler, ModelAndView mv, Exception exception) throws Exception {
boolean errorView = false;
if(exception != null) {
if(exception instanceof ModelAndViewDefiningException) {
this.logger.debug("ModelAndViewDefiningException encountered", exception);
mv = ((ModelAndViewDefiningException)exception).getModelAndView();
} else {
________________________________________________________________________
如果不是ModelAndViewDefiningException类异常则调用processHandlerException()方法
________________________________________________________________________
Object handler = mappedHandler != null?mappedHandler.getHandler():null;
mv = this.processHandlerException(request, response, handler, exception);
errorView = mv != null;
}
}

if(mv != null && !mv.wasCleared()) {
this.render(mv, request, response);
if(errorView) {
WebUtils.clearErrorRequestAttributes(request);
}
} else if(this.logger.isDebugEnabled()) {
this.logger.debug("Null ModelAndView returned to DispatcherServlet with name '" + this.getServletName() + "': assuming HandlerAdapter completed request handling");
}

if(!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
if(mappedHandler != null) {
mappedHandler.triggerAfterCompletion(request, response, (Exception)null);
}

}
}

如果存在异常且为非ModelAndViewDefiningException类异常,则执行processHandlerException

3.执行processHandlerException

protected ModelAndView processHandlerException(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
ModelAndView exMv = null;
Iterator var6 = this.handlerExceptionResolvers.iterator();
________________________________________________________________________
遍历开始时初始化的HandlerExceptionResolver列表,调用其resolveException方法
________________________________________________________________________
while(var6.hasNext()) {
HandlerExceptionResolver handlerExceptionResolver = (HandlerExceptionResolver)var6.next();
exMv = handlerExceptionResolver.resolveException(request, response, handler, ex);
if(exMv != null) {
break;
}
}

if(exMv != null) {
if(exMv.isEmpty()) {
request.setAttribute(EXCEPTION_ATTRIBUTE, ex);
return null;
} else {
if(!exMv.hasView()) {
exMv.setViewName(this.getDefaultViewName(request));
}

if(this.logger.isDebugEnabled()) {
this.logger.debug("Handler execution resulted in exception - forwarding to resolved error view: " + exMv, ex);
}

WebUtils.exposeErrorRequestAttributes(request, ex, this.getServletName());
return exMv;
}
} else {
throw ex;
}
}

自定义及使用异常处理器

1.实现HandlerExceptionResolver

public class MyExceptionResolver implements HandlerExceptionResolver {

private ExceptionLogDao exceptionLogDao;

@Override
public ModelAndView resolveException(HttpServletRequest request,
HttpServletResponse response, Object handler, Exception ex) {
__________________________________________________________
异常处理
__________________________________________________________
ModelAndView modelAndView = new ModelAndView("errorPage");
return modelAndView;
__________________________________________________________
若返回null则继续下一个HandlerExceptionResolver
__________________________________________________________
}
}

2.将此Bean配置到Spring容器中

<bean class="com.xxg.MyExceptionResolver" />

3.与web.xml中的error-page冲突问题

有HandlerExceptionResolver则跳转到HandlerExceptionResolver中的view,如果没有则使用web.xml的配置.