title: How to throw errors or exceptions from Action in Play?
body: <p>I read the official document of PlayFramework about Error handling. And I learned it is good to use <code>HttpErrorHandler</code> class.   And they say such error handling classes can catch errors or exceptions from <code>Action</code>.  And I saw methods of <code>DefaultHttpErrorHandler</code> class.  However, how does the <code>DefaultHttpErrorHandler</code> class distinguish errors or exceptions thrown from <code>Action</code>?  Some method such as <code>onServerError</code> takes <code>int</code> argument as its parameter, so in this case how does <code>Action</code> throw errors or exceptions? Does other page show it?</p>