Sorry Martin -- won't work the way you did it. Testing for null will
not throw an NPE. That's how we avoid an NPE all together.
However if you attempt to access a method on a null object reference, it
will throw an NPE. Example:
try {
javax.sql.DataSource dbds = null ;
dbds.getConnection() ; // This will definitely throw an NPE
} catch ( java.lang.NullPointerException npe ) {
// Do something else because we couldn't get a connection
}
Welcome to java programming 101.
Additionally some methods in various APIs will throw a NPE if you
provide a null value on a parameter.
--David
Martin Gainty wrote:
>the instant you execute code where a variable is NULL you will throw
NullPointerException
>if you want robust code you are better off wrapping in try catch block
as in
>try
>{
> if( in == null) System.out.println("This statement will never be
executed as NullPointerException will be thrown");
>}
>catch(NullPointerException npe)
>{
> System.out.println("variable in has thrown NullPointerException so
something about that here");
>}
>
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>contents
>----- Original Message -----
>From: "Christopher Schultz" <[EMAIL PROTECTED]>
>To: "Tomcat Users List" <users@tomcat.apache.org>
>Sent: Monday, November 13, 2006 2:57 PM
>Subject: Re: How do I ........?
>
>
> Steve,
>
> Steve R Burrus wrote:
>
> >hi chris this is steve Burrus and the line of code in question is the
> >while loop : "while( ( r = in.read(by)) != -1) {" the server error for a
> >long time has always pointed to that line of code creating the NPE.
>
> Yup, that's the first time you use the InputStream after attempting to
> load your file. It's pretty simple to check for null: just use the code
> I suggested in my last message:
>
> >>Correct me if I'm wrong, but this generally checks for null:
>
> >>if(null == in)
> >> // handle the null condition
>
> Now, it's up to you what you want to do in the event of a NULL image.
> You could either return a "404 Not Found" error status, or return a
> known good image that actually says "ERROR" on it.
>
> -chris
>
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