How can I pass a server side variable into a core tag in JSP?

问题

This expression tag outpus a correct value for me <%=drug.NonAuthoritative%>

while I cant recover the value of drug.NonAuthoritative for use in a C tag

<c:if test="${drug.NonAuthoritative}">&nbsp;<bean:message key="WriteScript.msgNonAuthoritative"></bean:message></c:if>

the method is

public Boolean NonAuthoritative() {
    return nonAuthoritative;
}

回答1:

There are 2 problems:

1. Scriptlets and EL do not share the same scope. The drug in ${drug} has to match the name of an existing attribute in the page, request, session or application scope. If you're preparing drug in a scriptlet instead of in a controller, then you should put it as an attribute in one of those scopes yourself.

   <% 
       Drug drug = new Drug();
       // ...
       request.setAttribute("drug", drug);
   %>
   

   ---

2. (as partly answered by Nathan), EL relies on Javabeans specification. The ${drug.propertyName} requires a public method getPropertyName() for non-boolean properties or isPropertyName() for boolean properties. So, this should do

   public class Drug {
   
       private boolean nonAuthorative;
   
       public boolean isNonAuthorative() {
           return nonAuthorative;
       }
   
       // ...
   }
   

   with

   <c:if test="${drug.nonAuthoritative}">
   

   (pay attention to the casing!)

回答2:

The scriptlet <%=drug.NonAuthoritative%> uses the field NonAuthoritative of the drug instance.

The EL expression ${drug.NonAuthoritative} uses the method isNonAuthoritative() of the drug instance.

To make this work, keep the EL expression as-is, but add this method to your drug class:

public boolean isNonAuthoritative() {
  return NonAuthoritative;
}

回答3:

That's because the JSTL is assuming you're using JavaBean standards, so when you call something drug.NonAuthoritative in a JSTL expression it's looking for a method called getNonAuthoritative() (or alternatively isNonAuthoritative()). The scriptlet doesn't make that assumption, it just evaluates what you give it.

来源：https://stackoverflow.com/questions/5859023/how-can-i-pass-a-server-side-variable-into-a-core-tag-in-jsp