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From Nick Pellow <>
Subject Re: Iterating over collections with null values
Date Mon, 05 Mar 2001 03:50:23 GMT

"Craig R. McClanahan" wrote:
> Bugzilla bug report #706 reports that you will get a JSP page exception
> when you try to iterate over collection that contains null values.  This
> is caused by the fact that the JSP page context refuses to allow null
> attributes.  The bug report suggests one alternative (although the
> proposed implementation has problems), but I would like to solicit
> suggestions and thoughts on what the correct behavior should be.
> Here are the alternatives that I can think of:
> (1)  No change -- document a restriction in the usage notes
>      on the <logic:iterate> tag.
> (2)  Silently skip this element of the iteration, with no notice
>      to the surrounding page.  The total number of times through
>      the loop, from the perspective of the page, will be less than
>      the size of the underlying collection.
> (3)  Do not skip this element, but don't add it to the page context
>      either.  The page can then use <logic:notPresent> to test for
>      whether the item is actually there or not.
> (4)  Do not skip this element, but insert a reference to a dummy
>      object instead of the null.  This is likely to cause class cast
>      exceptions, and is unlikely to be practical when the iteration
>      explicitly includes a "type" attribute.
> (5)  Other alternatives I have not thought of?

  (5) Add an attribute(s) on the iterate tag that allows the user to
decide between (1), (2) and (3). Defaulting to (1).

> All of the listed alternatives have their problems, but I am currently
> leaning towards (1).  Comments?  Suggestions?
> Craig McClanahan

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