Reviews : Adding Spice to Struts :

Adding Spice to Struts

by: Samudra Gupta

Last time when I published the article on Struts named "Strictly Struts", I had some requests to write something more on the topic. I am a big fan of Struts and find it so simple and elegant to use that it seems there is less of tricks in Struts to discuss. However, Ashish, one of my colleagues, presented me with a little problem, which provided the basis of this article. It is a problem with using dynamic form beans in Struts and we needed more than Struts normally provides.

The Problem

One afternoon Ashish and I were discussing a piece of work he was doing. All was coming along nicely but he was facing a problem of duplication of data in using DynaActionForm. He was trying to model an inheritance mechanism using DynaActionForm. For example, say, we are developing an online Vehicle registration system. Also let us assume that we want to register two types of Vehicle Car and Ship. The object model (Figure-1) of this problem domain inevitably looks something like the following:

Figure 1: The domain model for the Vehicle registration

We needed to replicate the similar relationship in the struts domain through ActionForms. As a strategy in our project, we use DynaActionForms. Listing –1 depicts what the initial form bean definitions looked like:

<form-bean name="CarForm" type="org.apache.struts.action.DynaActionForm">
      <form-property name="registrationNumber" type="java.lang.String"/>
      <form-property name="maker" type="java.lang.String"/><
      <form-property name="modelNumber" type="java.lang.Integer"/>

      <form-property name="engineSize" type="java.lang.Integer"/>
      <form-property name="noOfDoors" type="java.lang.Integer"/>
      <form-property name="insuranceGroup" type="java.lang.String"/>
  </form-bean>

  <form-bean name="ShipForm" type="org.apache.struts.action.DynaActionForm">
      <form-property name="registrationNumber" type="java.lang.String"/>
      <form-property name="maker" type="java.lang.String"/>
      <form-property name="modelNumber" type="java.lang.Integer"/>

      <form-property name="tonnage" type="java.lang.Integer"/>
      <form-property name="numberOfBoilers" type="java.lang.Integer"/>
      <form-property name="shipUsedAs" type="java.lang.String"/>
  </form-bean>

Listing-1: The initial form-bean definition

This solution will work fine without any problem in the real world. But rightly Ashish was not happy about the duplication of data in both the form beans (The bolded areas represent the duplicate data). Now we needed something more than what the default DynaActionForm offers in Struts. We both started thinking about a possible solution. Every solution to all problems requires a method in its approach. So we started from the basics of how Struts really handle the form-bean configurations internally.

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