JSF2.0 中UICommand 以及UIInput的一些注意事项

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用了一段JSF一段时间,基本原理算是有点明白了,可是涉及到前台的一些细节真的很让人头疼,比如说不通浏览器行为之间的差异,不通Server之间的差异.最近碰到个问题,库是基于JSF2.0的,当点击一个form中的按钮时,必须要点击两次才得到响应,在网上找了很多相关的解决方案,可是都不是很有效.好不容易找了一篇博客,有位大神对此类问题做了总结,在此对此总结进行分享(原文:http://stackoverflow.com/questions/2118656/hcommandlink-hcommandbutton-is-not-being-invoked/2120183#2120183)

Whenever an UICommand component fails to invoke the associated action method or anUIInput element fails to update the model value, then verify the following:

UICommand and UIInput components must be placed inside anUIForm component, e.g. <h:form>.
You cannot nest multiple UIForm components in each other. This is namely illegal in HTML. Watch out with include files!
No UIInput value validation/conversion error should have been occurred. You can use<h:messages> to show any messages which are not shown by any input-specific<h:message> components. Don't forget to include the id of<h:messages> in the <f:ajax render>, if any, so that it will be updated as well on ajax requests.
If UICommand or UIInput components are placed inside an iterating component like<h:dataTable>, <ui:repeat>, etc, then you need to ensure that exactly the samevalue of the component is been preserved during the apply request values phase of the form submit request. JSF will namely reiterate over it to find the clicked link/button and submitted input values. Putting the bean in the view scope and/or making sure that you load the data model in (post)constructor of the bean (and thus not in the getter method!) should fix it.
The rendered attribute of the component and all of the parent components should not evaluate tofalse during the apply request values phase of the form submit request. JSF will namely recheck it then as part of safeguard against tampered/hacked requests. Putting the bean in the view scope and/or making sure that you're preinitializing the condition in (post)constructor of the bean should fix it. The same applies to thedisabled attribute of the component, which should not evaluate to true during processing the form submit.
If you're using JSF 2.x <f:ajax> on the command component, make sure that you have a<h:head> in the master template instead of the <head>. Otherwise JSF won't be able to auto-include the necessaryjsf.js JavaScript file which contains the Ajax functions. This would result in a JavaScript error like "mojarra is not defined" in the browser's builtin JavaScript console.
If a parent of the <h:form> with the UICommand button is been rendered/updated by an ajax request beforehand, then the first action will always fail. The second and subsequent actions will work. This is caused by a bug in view state handling which is reported as JSF spec issue 790 and fixed in JSF 2.2. For JSF 2.0 and 2.1 you need to explicitly specify the ID of the<h:form> in the render of the <f:ajax>.
If the <h:form> has enctype="multipart/form-data" set in order to support file uploading, then you need to make sure that the servlet filter who is responsible for parsing multipart/form-data requests is properly been configured, otherwise the FacesServlet will end up getting no request parameters at all and thus not be able to apply the request values. How to configure such a filter depends on the file upload component being used. For Tomahawk<t:inputFileUpload>, check this answer and for PrimeFaces <p:fileUpload>, check this answer. Or, if you're actually not uploading a file at all, then remove the attribute altogether.
Be sure that the ActionEvent argument of actionListener is anjavax.faces.event.ActionEvent and thus not java.awt.event.ActionEvent, which is what most IDEs suggest as 1st autocomplete option.
Be sure that no PhaseListener or any EventListener in the request-response chain has changed the JSF lifecycle to skip the invoke action phase by for example callingFacesContext#renderResponse() or FacesContext#responseComplete().
Be sure that no Filter or Servlet in the same request-response chain has blocked the request fo theFacesServlet somehow.

My bet that your particular problem is caused by point 2: nested forms. You probably already have a<h:form> in the parent page which wraps the include file. The include file itself shouldnot have a <h:form>. You can also fix it the other way round, ensure that the parent page doesnot have a <h:form> around the place of the include file.