Reference interface constant from EL

Question

How do you reference an interface constant with EL on a JSP page?

I have an interface Addresses with a constant named URL. I know I can reference it with a scriplet by going: <%=Addresses.URL%>, but how do I do this using EL?

Answer 1

You can't. It follows the Java Bean convention. So you must have a getter for it.

Answer 2

You usually place these kinds of constants in a Configuration object (which has getters and setters) in the servlet context, and access them with ${applicationScope.config.url}

Answer 3

This is not possible using standard EL. There are however several ways to achieve the requirement:

1. Put them in a Map<String, Object> which you put in the application scope. In EL, map values are accessible the usual Javabean way by ${map.key} or ${map['key.with.dots']}.

2. Use <un:useConstants> of the Unstandard taglib:

   <%@ taglib uri="http://jakarta.apache.org/taglibs/unstandard-1.0" prefix="un" %>
   <un:useConstants className="com.example.YourConstants" var="constants" />
   

   This way they are accessible the usual Javabean way by ${constants}.

3. Use Javaranch's CCC <ccc:constantsMap> as desribed somewhere at the bottom of this article.

    <%@ taglib uri="http://bibeault.org/tld/ccc" prefix="ccc" %>
    <ccc:constantsMap className="com.example.YourConstants" var="constants" />
   

   This way they are accessible the usual Javabean way by ${constants} as well.