Should I add try/catch around when casting on an attribute of JSP implicit object?
- by Michael Mao
Hi all:
Basically what I mean is like this:
List<String[]> routes = (List<String[]>)application.getAttribute("routes");
For the above code, it tries to get an attribute named "routes" from the JSP implicit object - application. But as everyone knows, after this line of code, routes may very well contains a null - which means this application hasn't got an attribute named "routes".
Is this "casting on null" good programming practice in Java or not?
Basically I try to avoid exceptions such as java.io.InvalidCastException
I reckon things like this are more as "heritage" of Java 1.4 when generic types were not introduced to this language. So I guess everything stored in application attributes as Objects (Similar to traditional ArrayList). And when you do "downcast", there might be invalid casts.
What would you do in this case?
Update:
Just found that although in the implicit object application I did store a List of String arrays, when I do this :
List<double[]> routes = (List<double[]>)application.getAttribute("routes");
It doesn't produce any error... And I felt not comfortable already...
And even with this code:
out.print(routes.get(0));
It does print out something strange :
[Ljava.lang.String;@18b352f
Am I printing a "pointer to String"? I can finally get an exception like this:
out.print(routes.get(0)[1]);
with error :
java.lang.ClassCastException: [Ljava.lang.String;
Because it was me to add the application attribute, I know which type should it be cast to. I feel this is not "good enough", what if I forget the exact type?
I know there are still some cases where this sort of thing would happen, such as in JSP/Servlet when you do casting on session attributes. Is there a better way to do this?
Before you say:"OMG, why you don't use Servlets???", I should justify my reason as this: - because my uni sucks, its server can only work with Servlets generated by JSP, and I don't really want to learn how to fix issues like that. look at my previous question on this
, and this is uni homework, so I've got no other choice, forget all about war, WEB-INF,etc, but "code everything directly into JSP" - because the professors do that too. :)
