Java(TM) Boutique - Advanced Forms Handling in Struts 1.1

Tutorials : Advanced Forms Handling in Struts 1.1 :

Dynamic options

It's much more interesting--seen from a programmer's point of view--when the selectable options are computed in the application, for example read from a database. Struts has solutions for all the remaining controls--marked 4, 5, 6, and 7 above--but unfortunately they're rather different. One thing is, however, common for some of them: they use the logic:iterate tag to loop over the set of selectable options. So let's take a quick recap of how to use the iterate tag. A simple example:

<table border=1> 
  <logic:iterate id="customer" name="customers">
    <tr>
      <td><bean:write name="customer" property="firstName"/></td>
      <td><bean:write name="customer" property="lastName"/></td>
      <td><bean:write name="customer" property="address"/></td>
   </tr>
  </logic:iterate>
</table>

The iterate tag's name-attribute refers to a Collection of beans stored in request or session scope. The id-attribute gives the (logical) name of the bean created in each iteration. Other tags--for example the bean:write tag--may then refer to this bean with their name-attribute. The property-attribute finally selects the wanted property from the bean.

You might now think that you simply use the name-and property-attributes with the html-tags, but it's not that simple. The html-tags already use the property- attribute for the name of the property in the ActionForm, so there's a conflict here.

The tag inventors have had other challenges as well, so therefore the syntax for the HTML-tags when handling sets of options are a bit heterogeneous.

The Radio Button

Now I'll present a solution, and afterwards discuss the explanations. First the struts-config file, where we define a dynamic form bean (but you could just as well use the old ActionForm bean):

<form-bean name="radioForm"
  type="org.apache.struts.action.DynaActionForm">
  <form-property name="control" type="java.lang.String"/>
</form-bean>

Then the jsp-code:

<logic:iterate id="choice" name="choices">
  <html:radio property="control" idName="choice" value="value"/>
  <bean:write name="choice" property="label"/>
  <br>
</logic:iterate>

We're using a Collection of beans with properties value and label. When the idName attribute is used the radio-tag's value-attribute denotes a property in the bean given by idName. It's the id-attribute in the iterate-tag and the idName in the radio-tag that links the tags together.

Struts has a utility bean class called LabelValueBean with exactly these properties: value and label, and it may be used to construct a "minimal" bean to put in a Collection, for example:

import org.apache.struts.util.LabelValueBean;
. . .
Collection choices = new ArrayList();

choices.add(new LabelValueBean("American Express", "AE"));
choices.add(new LabelValueBean("MasterCard", "MC"));
choices.add(new LabelValueBean("Diners", "DN"));

request.setAttribute("choices", choices);

You don't have to use this utility class, any bean will do, as long as it has properties that can be used for the value attribute in the html:radio tag and the property attribute in the bean:write tag.

You may set or get the current value of the radio buttons in the execute method, as described earlier. The name we've used for the radio buttons, control, will also be used in the following examples.

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