How to display a different JSP view for different types of objects

Question

Assuming I have a list of Animal(s) with standard polymorphic behavior like Cat(s) and Dog(s).

What is the best approach to display a different JSP view for each one in the list?

<c:forEach var='animal' items='${animals}'>
 //show a different template per animal type
</c:forEach>

To be honest having a #toJSP for each bean is something I wouldn't consider for obvious reasons.

I am tempted however of using a

public interface Template{

  public String render()
}

with each Animal passed in the constructor, however I'm not sure where these objects should be created. I guess it can be done inside the JSP in a <%%> but I'm hesitant using this notation for some reason.

So I ended up using the "bundles" that are available for i18n in JSP in the following way

<fmt:message var="template" key="${animal.class.name}" />

with a template.properties file

foo.bar.Animal = animal.jsp 
foo.bar.Cat = cat.jsp
foo.bar.Dog = dog.jsp

So the final solution would look like this

<c:forEach var='animal' items='${animals}'>
 <span>
  <c:set var="animal" scope="request" value="${animal}"/>
  <fmt:message var="template" key="${animal.class.name}" />
  <jsp:include page="${template}" />
 </span>
</c:forEach>

With template files that looks like this

Hello animal ${animal}!
Hello cat ${animal}!
Hello dog ${animal}!

Answer 1

Declare an abstract method on Animal that returns a string, called getMyJspPage().

Then cats and dogs can return a reference to a different jsp page or jsp fragment that you can include.

Answer 2

You could use a custom tag that takes the current animal as an attribute and uses it to determine the correct view

Answer 3

Unfortunately, inheritance and polymorphism doesnt work in jsps very well.

The easiest, and most maintainable solution has been to just do a lot of

<c:choose>
   <c:when test="${animal.type == 'Cat'}">
      <my:renderCat cat="${animal}"/>
   </c:when>
   <c:when test="${animal.type == 'Dog'}">
      <my:renderDog Dog="${animal}"/>
   </c:when>
   ...
</c:choose>

and have tag files (like renderDog.tag, renderCat.tag) that takes each specific animal as an attribute, and call out to them. at least it keeps the dispatching, and the rendering seperated.