Where can the variable in jsp be defined except java classes?

Question

Suppose I have the following code:

<c:when test="${isFoo}">

Where can isFoo be defined except:

1. java classes
2. <c:set ... /> construction ?

Answer 1

1. In JSP itself by scriptlets. E.g. as a request attribute:

   <% request.setAttribute("isFoo", true); %>
   

   Scriptlets are however discouraged since over a decade.

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2. By an implicit EL variable. E.g. as a request parameter:

   http://example.com/page.jsp?isFoo=true

   Which can be accessed by ${param}:

   <c:if test="${param.isFoo}">
   

   There are many more, you can find them all in this overview.

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See also:

• Our EL (Expression Language) tag wiki page

Answer 2

You can also set it using c:set. For instance:

<c:set var="isFoo" value="true" scope="page" />