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From: Chris Riesbeck <Chris.Riesbeck@gmail.com>
Newsgroups: comp.lang.java.programmer
Subject: JSTL: getting a map's keys
Date: Mon, 19 Mar 2012 13:15:52 -0500
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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>