Re: JSTL: getting a map's keys

From:

Lew <lewbloch@gmail.com>

Newsgroups:

comp.lang.java.programmer

Date:

Tue, 20 Mar 2012 11:05:14 -0700 (PDT)

Message-ID:

<14359232.4616.1332266714833.JavaMail.geo-discussion-forums@pbcr5>

Chris Riesbeck wrote:

Daniel Pitts wrote:

Chris Riesbeck wrote:

[summary: rates is an instance of a subclass of Map that
implements getKeys()]

Why does ${rates.keys} generate nothing in these lines of JSP?

My guess is that ${rates.keys} is interpreted as equivalent to
${rates['keys']}, so it is looking for a key of "keys", not a java bean
property.

Just to nail the coffin lid shut on this. The JSP EL defines name.key as=

just shorthand for name["key"]. To interpret [] expressions, JSP uses
the first answer it gets from this chain of resolvers:

     ImplicitObjectELResolver
     registered custom ELResolvers
     MapELResolver
     ListELResolver
     ArrayELResolver
     BeanELResolver
     ScopedAttributeELResolver

http://docs.oracle.com/javaee/5/api/javax/servlet/jsp/JspApplicationConte=

xt.html

So the Map interpretation will always override the Bean interpretation.

Now that your main question is answered, a couple of comments are in order.

- Don't have scriptlet in your JSPs.
- 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 bee=
n 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.

--
Lew