Re: JSTL: getting a map's keys

From:
Daniel Pitts <newsgroup.nospam@virtualinfinity.net>
Newsgroups:
comp.lang.java.programmer
Date:
Tue, 20 Mar 2012 11:28:38 -0700
Message-ID:
<q%3ar.13283$fj7.687@newsfe20.iad>
On 3/20/12 10:52 AM, Chris Riesbeck wrote:

On 3/20/2012 12:19 PM, Chris Riesbeck wrote:

On 3/19/2012 6:59 PM, Daniel Pitts wrote:

On 3/19/12 11:15 AM, 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/JspApplicationContext.html

So the Map interpretation will always override the Bean interpretation.


Another interesting side-effect of this approach is that
SomeObject.property might attempt to parse "property" as a number if
SomeObject implements List. We've had this problem where a generic class
which converts XML->Maps/Lists/Strings used different types depending on
the multiplicity of specific tags. (It was bad design IMO, but I was
politically unable to have it designed otherwise).

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