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From: Chris Riesbeck <Chris.Riesbeck@gmail.com>
Newsgroups: comp.lang.java.programmer
Subject: Re: JSTL: getting a map's keys
Date: Tue, 20 Mar 2012 12:19:42 -0500
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On 3/19/2012 6:59 PM, Daniel Pitts wrote:
> On 3/19/12 11:15 AM, Chris Riesbeck wrote:
>> Can anyone help me figure out why the following is happening, or further
>> experiments I can run? (I have workarounds but I'd like to know what I'm
>> misunderstanding.)
>>
>> Given:
>> - SimTable, a subclass of HashTable that defines getKeys() to call
>> keyset()
>> - a session variable "data" which is a HashTable with "rates" set to an
>> instance of a SimTable
>>
>> Why does ${rates.keys} generate nothing in these lines of JSP?
>>
>> <c:set var="rates" value='${data["rates"]}'/>
>>
>> <p>rates: ${rates}</p>
>>
>> <p>jstl: ${rates.keys}</p>
>>
>> <p>jsp: <%= ((edu.northwestern.ils.simulator.SimTable)
>> pageContext.findAttribute("rates")).getKeys() %></p>
>>
>> Here's the generated HTML output:
>>
>> <p>rates: {Bill=100.0, Fred=75.0, Jane=75.0, Mary=50.0, Sam=75.0,
>> Sarah=150.0}</p>
>>
>> <p>jstl: </p>
>>
>> <p>jsp: [Bill, Fred, Jane, Mary, Sam, Sarah]</p>
>>
> 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.

Ah! This would explain why ${rates.class} doesn't work either. 
Basically, name.key will always be taken as name[key] for a Map, even if 
key is a property of name. If I'm reading the JSP EL resolver 
specification correctly, that's just what is happening.

>
> You *can* use c:forEach to iterate over the entry set (Map.Entry) in a map.

Yes, that's what I've been doing instead for looping.

>
> Hopefully this helps,
> Daniel.

Indeed. Thanks, Daniel