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在struts中,通常采用的全局错误控制模式是构建一个baseAction,在其execute方法中完成前台传回方法的dispatch操作,并由 try……catch……捕获程序错误,实现错误的控制和展示。一个典型的BaseAction例子如下:
代码
public ActionForward execute(ActionMapping mapping, ActionForm form, HttpServletRequest request, HttpServletResponse response) { …… ActionForward forwardPage = null; try { String parameter = mapping.getParameter(); if (parameter == null) { String message = messages.getMessage("dispatch.handler", mapping.getPath()); response.sendError(500, message); return null; } String name = processReqCode(request.getParameter(parameter)); forwardPage = dispatchMethod(mapping, form, request, response, name); } catch (BaseException ex) { if (log.isDebugEnabled()) log.debug("发生错误:", ex); forwardPage = processBaseException(request, mapping, ex); } catch (Throwable ex) { log.error("发生错误:", ex); ActionMessages errors = new ActionMessages(); ByteArrayOutputStream ostr = new ByteArrayOutputStream(); ex.printStackTrace(new PrintStream(ostr)); errors.add("org.apache.struts.action.GLOBAL_MESSAGE", new ActionMessage(ostr.toString())); saveErrors(request, errors); forwardPage = mapping.findForward("syserror"); output.setStatus("fail"); output.setError(ex.getMessage()); } …… } |
由于JSF采用了managed bean,JSP页面直接通过调用managed bean中的方法完成数据交互,不能像struts一样通过捕获dispatch操作过程抛出的异常来完成错误的处理(因为根本就没有dispatch方法),似乎jsf根本就不支持全局的错误处理。
如果在managed bean中throw 一个exception(这里是AppException),观察一下控制台的日志,可以看到其实错误是从一个ActionListener的实现中抛出的(针对myfaces,这里是ActionListenerImpl),参考jsf的生命周期过程,方法出来了:
代码
public class GlobalActionListener extends ActionListenerImpl { public void processAction(ActionEvent event) throws AbortProcessingException { FacesContext facesContext = FacesContext.getCurrentInstance(); Application application = facesContext.getApplication(); ActionSource actionSource = (ActionSource) event.getComponent(); MethodBinding methodBinding = actionSource.getAction(); String fromAction = null;String outcome = null; if (methodBinding != null) { fromAction = methodBinding.getExpressionString(); try { outcome = (String) methodBinding.invoke(facesContext, null); } catch (EvaluationException e) { Throwable cause = e.getCause(); if (cause != null && cause instanceof AppException) { //这里需要根据框架的不同,判断实例是否是程序中手动抛出的错误 FacesUtils.addErrorMessage(event.getComponent().getClientId(facesContext),cause.getMessage());} else { throw (AbortProcessingException) cause; } } catch (RuntimeException e) { throw new FacesException("Error calling action method of component with id " + event.getComponent().getClientId(facesContext), e); } NavigationHandler navigationHandler = application.getNavigationHandler(); navigationHandler.handleNavigation(facesContext, fromAction, outcome); // Render Response if needed facesContext.renderResponse(); } } |
监听器配置,faces-config-application.xml:
代码
<application> <variable-resolver>org.springframework.web.jsf.DelegatingVariableResolver</variable-resolver> <message-bundle>resources.application</message-bundle> <locale-config> <default-locale>en</default-locale> </locale-config> <action-listener>org.snailportal.webframework.listener.GlobalActionListener</action-listener> </application> |
这样,开发人员只需要在action和managed bean里面根据业务的需要抛出指定基础类型的Exception实例,由BaseAction和ActionListener完成错误的封装处理,再传递给前台进行显示,从而减少开发的代码量,提高框架的可维护性。
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