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JSF和Struts框架的错误控制与封装处理_0

发布时间:2019-09-12 18:02:15

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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