问题描述
为什么从不同于的上下文中调用 RequestContext rq = RequestContext.getCurrentInstance()会引发 NullPointerException 吗?
Why calling RequestContext rq = RequestContext.getCurrentInstance() from a different context than FacesContext throws a NullPointerException ?
我无法执行以下操作:
RequestContext rq = RequestContext.getCurrentInstance() //NPE is thrown
if (rq != null) {
..
}
我想做的是在 WebFilter 中检索一个bean并调用一个方法.此方法使用上面的代码段；因此会抛出 NullPointerException .
What I am trying to do is to retrieve a bean inside a WebFilter and call a method. This method uses above snippet; so it throws NullPointerException.
谢谢您的帮助.
推荐答案
RequestContext 的实例另存为 FacesContext 中的属性，因此当没有时FacesContext ，您将拥有NPE.这是告诉您如何获取 RequestContext 的代码，该代码将被清除:
Instance of RequestContext is saved as an attribute in FacesContext, so when there is not FacesContext you will have NPE. Here is the code which will tell you how RequestContext is obtained, and that will be cleared:
return (RequestContext) FacesContext.getCurrentInstance().getAttributes().get(Constants.REQUEST_CONTEXT_ATTR);
创建 RequestContext 并将其另存为 FacesContext 属性是在 还原视图阶段 ，因此它在您的过滤器中不存在.
Creating RequestContext and saving it as FacesContext attribute is done in PhaseListener of Primefaces, after Restore view phase, so it doesn't exist in your filter.
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