jsp - Access map value in EL using a variable as key

Question

I have a Map in EL as ${map} and I am trying to get the value of it using a key which is by itself also an EL variable ${key} with the value "1000".

Using ${map["1000"]} works, but ${map["$key"]} does not work. What am I doing wrong and how can I get the Map value using a variable as key?

Answer 1

$ is not the start of a variable name, it indicates the start of an expression. You should use ${map[key]} to access the property key in map map.

You can try it on a page with a GET parameter, using the following query string for example ?whatEver=something

<c:set var="myParam" value="whatEver"/>
whatEver: <c:out value="${param[myParam]}"/>

This will output:

whatEver: something

See: https://stackoverflow.com/tags/el/info and scroll to the section "Brace notation".