Create "Dynamic" beans to handle dynamic form

Question

Hi All,
Hope it is not too stupid question.
JSP is all about dynamic content, a part of which can be a form that displays different fields and attributes. If I use Javabeans to handle the form, I will need different beans to go with each "configuration" of the form.
Now let's say I have a form that can get one of three "configurations" , depanding on the parameter passed to the JSP page.
I can create three Beans to match any type of form. (e.g., AFormBean, BFormaBean, CFromBean)
How can I conditionally instansiate the Bean to handle the not yet known type of the Form?
I tried to use an abstract Bean to be defined on the top of the JSP :
<%
Beans.AddComponentBean addComponentBean;
%>
    <c:choose>
        <c:when test='${param.type=="DBMS"}'>
                <jsp:useBean id="addComponentBean"            
                   class="Beans.AddDBMSBean" scope="page"/>
                <jsp:setProperty name="addDBMSBean" property="*"/>    
        </c:when> 
        <c:when test='${param.type=="APP"}'>
                <jsp:useBean id="addComponentBean"
                      class="Beans.AddAppBean" scope="page"/>       
                <jsp:setProperty name="addDBMSBean" property="*"/>    
        </c:when>                 
        </c:choose>
But that cannot be done since I get Use Bean duplicate.
What is the right way of doing this?
Thanks.

Answer 1

How I would do this depends on my application design.
I think I would go with a Factory type of design. I would have an 'AddBeanFactory' that decides on the specific type of the bean to create, and returns the abstract AddComponentBean. If you want to do it all in JSP, then making the factory a bean itself is usefull:
package beans;
import java.util.Map;
import java.util.HashMap;
public class AddBeanFactory {
     private String type;
     private Map parameters;
     private AddComponentBean addComponentBean;
     private static final Map<String, Class<? extends AddComponentBean>>TYPEMAP = new HashMap<String, Class<? extends AddComponentBean>>();
     static {
          TYPEMAP.put("DBMS", beans.AddDBMSBean.class);
          TYPEMAP.put("APP", beans.AddAppBean.class);
     public AddBeanFactory() {}
     public void setType(String type) { this.type = type; }
     public void setParameters(Map params) { this.parameters = params; }
     public AddComponentBean getAddComponentBean() throws InstantiationException, IllegalAccessException {
          if (addComponentBean == null) {
               if (type==null || parameters == null){
                    throw new IllegalStateException("The Component Type and Parameters must be set prior to retrieving the ComponentBean");
               addComponentBean = TYPEMAP.get(type).newInstance();
               //fill bean with parameters
          return addComponentBean;
}Then your JSP would be something like:
<jsp:useBean id="beanFactory" class="beans.AddBeanFactory" scope="page">
    <jsp.setProperty name="beanFactory" property="type"/>
    <jsp.setProperty name="beanFactory" property="parameters" value="${request.parameterMap}"/>
</jsp:useBean>
<c:set var="addComponentBean" value="${beanFactory.addComponentBean}"/>