Question

Let’s say I’ve got two request attributes coming:

1. “fieldnames” which is a list of field names. example: [“fielda”, “fieldb”]
2. “field.fielda” which contains a snippet of html. example: an input field or something like that

In my JSP page I’ve got something like the following:

<c:forEach var="field" value="${fieldnames}">
  <c:set var="tmp" value="field.${field}"/>
  ${request.getAttribute(tmp)}
</c:forEach>

Now the problem, I can see the name of the field via the list. I can generate in a temp variable the “proper” field name. But I can’t figure out how to get the value of the referenced attribute from the request attribute map. Can this be done? I’ve tried using the request[variable] notation as well to no avail.

Answer 1

Assuming you have a bean like:

public class MyBean {
   private String fielda;
   private String fieldb;

   public String getFielda() {
      return fielda;
   }
   public void setFielda(String fielda) {
      this.fielda = fielda;
   }
   public String getFieldb() {
      return fieldb;
   }
   public void setFieldb(String fieldb) {
      this.fieldb = fieldb;
   }
}

with code somewhere that does:

MyBean field = new MyBean();
field.setFielda("Message from A");
field.setFieldb("Message from B");
request.setAttribute("field", field);

request.setAttribute("fieldnames", new String[] { 
   "fielda", "fieldb" 
});

then something like this should work:

<c:forEach var="fn" items="${fieldnames}">
   ${requestScope.field[fn]}
</c:forEach> 

If that fails, or your code is more complex than that, you could pull out the logic in a custom tag or a custom function to do the EL evaluation. If that’s too much overhead for the situation, then maybe you could rethink your code and find another way for obtaining the same result.