ServletContext何时返回null RequestDispatcher？ [英] When does the ServletContext return a null RequestDispatcher?
问题描述
ServletContext＃getRequestDispatcher（）说：
如果ServletContext无法返回RequestDispatcher，则此方法返回null。
This method returns null if the ServletContext cannot return a RequestDispatcher.
和
返回：
a RequestDispatcher对象，充当指定路径上资源的包装，如果ServletContext无法返回RequestDispatcher，则返回null
Returns: a RequestDispatcher object that acts as a wrapper for the resource at the specified path, or null if the ServletContext cannot return a RequestDispatcher
For ServletContext无法返回RequestDispatcher的原因是什么？起初我认为如果传递了无效路径但是没有返回null，则会在浏览器上产生404.
For what reason would the ServletContext not be able to return a RequestDispatcher? At first I figured it would be if an invalid path was passed but that doesn't return null, it results in a 404 on the browser.
我正在检查null在调用forward（）方法之前，在日志中我可以看到，曾经有一段时间RequestDispatcher为null，但我不知道为什么，我无法找到如何复制它。
I am checking for null before calling the forward() method and in the logs I can see that once in awhile the RequestDispatcher is null but I don't know why and I can't find out how to duplicate it.
谢谢
更新
像Fazal建议我试过为'http://www.google.com/'创建了一个RequestDispatcher，看看会发生什么。这导致了IllegalArgumentException
Like Fazal suggested I tried created a RequestDispatcher to 'http://www.google.com/' to see what would happen. This caused an IllegalArgumentException
java.lang.IllegalArgumentException：Path http://www.google.com/ 不以/字符开头
Exception在我的try / catch块中被捕获，因此我没有机会检查RequestDispatcher是否为null或调用forward（）方法。
The Exception was caught in my try/catch block so I never got the chance to check if the RequestDispatcher was null or call the forward() method.
因此，ServletContext＃getRequestDispatcher（）方法必须有另一种方法返回null而不抛出异常？
So there must be another way for the ServletContext#getRequestDispatcher() method to return null without throwing an Exception?
推荐答案
Tomcat为当前上下文之外的路径返回 null ，例如 /../ foo （但Jetty没有，因此它是特定于实现的。）
Tomcat returns null for path outside of the current context, such as /../foo (but Jetty doesn't, so it's implementation-specific).
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