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unable to understand paramValues implicit Object

Mohit G Gupta
Ranch Hand

Joined: May 18, 2010
Posts: 634


param.jsp contains
code from
jstl 1.0 specification

Here ,paramValues is map that contains multiple key value pair.

then,first time the loop executes aParam.key gives key of first element of Map
1.why is foreach required ?
2.can we have the following code instead of the above one ?

i got the following output .


I am unable to get how paramValues stores the request parameters .
I thought aParam.Key would give the Key and aParam.value would give the value .

OCPJP 6.0 93%
OCPJWCD 5.0 98%
Paul Clapham

Joined: Oct 14, 2005
Posts: 19357

Well, no. Since a request can include more than one parameter with the same name, the request contains an array of strings for the value of each parameter. That's what you are seeing in that debugging output.
Frits Walraven
Creator of Enthuware JWS+ V6

Joined: Apr 07, 2010
Posts: 1927

What Paul is saying is correct and I just want to add some explanation.

  • paramValues is a Map of all ServletRequest parameter names and all values, like you get when you do this String[] values = request.getParameterValues(String paramName), so for every paramName there is a String[] containing the values
  • If you have a querystring like this: URL?myParam="first"&myParam="second" you can get to the individual entries like this:

  • ${paramValues.myParam[0]} -> first
    ${paramValues.myParam[1]} -> second

    Don't get me started about those stupid light bulbs.
    subject: unable to understand paramValues implicit Object