Re: JSTL: getting a map's keys

From:

Lew <lewbloch@gmail.com>

Newsgroups:

comp.lang.java.programmer

Date:

Thu, 22 Mar 2012 13:23:34 -0700 (PDT)

Message-ID:

<11405563.61.1332447814183.JavaMail.geo-discussion-forums@pbctp7>

Chris Riesbeck wrote:

Lew wrote:

Chris Riesbeck wrote:

Lew wrote:

- If you had *composed* a 'Map' into a custom class rather than
inheriting 'Map', you would not have had the problem. Your custom
class would have been resolved by the bean resolver. - This in turn
would make for a better design overall. Instead of your view artifact
(the JSP) caring about the implementation details of the map and its
set of keys, you'd have a controller call like 'getKeys()' or
whatever that would cleanly separate the logic of how you get them
from presentation concerns.

Using delegation (my preference also) doesn't support the JSP EL form
${rates["Bill"]}. If I had a custom class, I'd need a custom tag or
custom EL
resolver to make that work.

No, you most certainly would not.

Just define an appropriate method in your class.

Color me totally dense. Maybe I'm missing what method I should be defining.

If my class implements the Map interface, then MAPElResolver will be
invoked and do the same thing with name.key and name["key"]: call
name.get("key"). The JSP EL won't be able to call any bean method of name.

If my class doesn't implement Map, then BeanELResolver will be invoked
and do the same thing with name.key and name["key"]: call name.getKey().
The JSP EL won't be able to call name.get() via [].

So I don't see how I can have a class such that in the JSP EL I can call
a method to get all the keys, and also retrieve data with a key using [].

I was thinking along the lines of this incompletely worked-through notion:

public class ContactScreenBacker
{
   private final Map<String, Rate> rates = howeverYouSetItUp();
   public Map<String, Rate> getRates() { return Collections.unmodifiableMap(rates); }
   public Set<String> getKeys() { return Collections.unmodifiableSet(rates.getKeys(); }
// ...
}

You should be able to use an EL like '#{thingie.rates["Bill"]}'. I haven't tried it, but this is what I had in mind.

--
Lew