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JSF和Struts框架的错误控制与封装处理

2020-05-06 19:56:34
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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



org.springframework.web.jsf.DelegatingVariableResolver

resources.application

en


org.snailportal.webframework.listener.GlobalActionListener


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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