Re: JSTL: getting a map's keys

From:

Daniel Pitts <newsgroup.nospam@virtualinfinity.net>

Newsgroups:

comp.lang.java.programmer

Date:

Mon, 19 Mar 2012 16:59:24 -0700

Message-ID:

<xLP9r.4373$dq4.2106@newsfe23.iad>

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"]}'/>

rates: ${rates}

jstl: ${rates.keys}

jsp: <%= ((edu.northwestern.ils.simulator.SimTable)
pageContext.findAttribute("rates")).getKeys() %>

Here's the generated HTML output:

rates: {Bill=100.0, Fred=75.0, Jane=75.0, Mary=50.0, Sam=75.0,
Sarah=150.0}

jstl: 

jsp: [Bill, Fred, Jane, Mary, Sam, Sarah]

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.

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

Hopefully this helps,
Daniel.