Tomcat 6.0 does not allow generic ArrayList to be used for useBean

Question

In a jsp file I have this declaration:

<jsp:useBean scope="request" id="products" class="java.util.ArrayList<sgt.supermarket.entity.Product>"/>

This declaration works fine with GlassFish 2.1, however, when I switch to Tomcat 6.0, exceptions is thrown:

The value for the useBean class attribute java.util.ArrayList is invalid.

Is there any library missed for Tomcat that makes it behave different from Glass Fish 2.1?

Answer 1

EL isn't aware of parameterized types, so there is no need to do so. In JSP/EL there are absolutely no compile-time checks on that. EL is more based on reflection. I am however a bit surprised that it "works" in Glassfish as it isn't specified in JSP/EL specifciation.

Apart from it all, the jsp:useBean is fairly superfluous in a decent MVC application wherein a Servlet is been used to control and preprocess the requests.

List<Product> procucts = productDAO.list();
request.setAttribute("products", products);
request.getRequestDispatcher("products.jsp").forward(request, response);

The products is now just accessible in EL by ${products}. No need for a jsp:useBean.

Answer 2

If you are dealing with legacy code and simply want to get rid of all those raw-type JSP warnings then you may want to replace your line with this one:

<% request.setAttribute("products", 
       new java.util.ArrayList<sgt.supermarket.entity.Product>()); %>

But BalusC is still right: When you use the classic MVC pattern then it is better to create this product list in the controller and not in the view. And if you are using a view-first pattern then I suggest writing your own JSP Tag which creates and fills this product list in clean Java Code.