How do I use form beans in Spring MVC? - forms

Question

I'm new to Spring MVC (3.1.1). Coming from a Rails and Struts1 world that is.
In Struts, our FormBeans automatically map to our controllers. For example:
# JS file
ExtJS.ajax({action:'update', value:42});
Then our controller can:
bean.getAction(); // 'update'
bean.getValue(); // 42
We instantiate the bean like:
public ActionForward execute(ActionMapping mapping, ActionForm form,
HttpServletRequest request, HttpServletResponse response)
throws Exception {
MyBean bean = (MyBean) form;
....
}
Please forgive my ignorance, but how would I do the same thing in Spring MVC?

Answer 1

In jsp do something like this :
<%# taglib uri="http://www.springframework.org/tags/form" prefix="form"%>
<form:form name="frmFoo" id="frmFoo" action="/FormSubmitUrl" method="POST" modelAttribute="foo">
<form:select path="myField">
<form:errors path="myField" />
</form:form>
And just add the backing object to the model in your controller method :
#RequestMapping(value = "/MyFooForm", method = RequestMethod.GET)
public String getFoo(final Model model)
{
model.addAttribute("foo", foo);
return "fooForm.jsp";
}

Answer 2

Am going from, Spring MVC - Rails. I like Rails lot better :-). There are lot of start up tutorials for Spring MVC. But spring has a good tutorial that you can follow. But to begin with you will have to start with the spring-dispatch-servlet.xml. There you will define your association between views, controller and form. For example in this following snippet:
<bean name="/priceincrease.htm" class="springapp.web.PriceIncreaseFormController">
<property name="sessionForm" value="true"/>
<property name="commandName" value="priceIncrease"/>
<property name="commandClass" value="springapp.service.PriceIncrease"/>
<property name="validator">
<bean class="springapp.service.PriceIncreaseValidator"/>
</property>
<property name="formView" value="priceincrease"/>
<property name="successView" value="hello.htm"/>
<property name="productManager" ref="productManager"/>
</bean
Controller is the PriceIncreaseFormController and the priceIncrease is the equivalent command object. The corresponding view i.e. JSP will have
<form:form method="post" commandName="priceIncrease">
<table width="95%" bgcolor="f8f8ff" border="0" cellspacing="0" cellpadding="5">
<tr>
<td align="right" width="20%">Increase (%):</td>
<td width="20%">
<form:input path="percentage"/>
</td>
<td width="60%">
<form:errors path="percentage" cssClass="error"/>
</td>
</tr>
</table>
But I think you might get a complete picture from this place where I picked up the code from
http://static.springsource.org/docs/Spring-MVC-step-by-step/part4.html#step4.5 and the place where you can get Spring MVC's example code base is https://src.springframework.org/svn/spring-samples/mvc-basic

Answer 3

I was looking for this answer today based on some code in a project I inherited. What I found was that the if you create a controller action on a multiActionController. The form values can be mapped to a bean that would be the third paarameter on your handler action.
In my case I had a controller like this
public void submit(HttpServletRequest request,
HttpServletResponse response, SomeBean sb) {
{
//do something with sb - SomeBean
}
My issue was in figuring out how the values in my form were mapped to the controller action. There was no reference at all to the SomeBean within my jsp form. As it turns out Spring works the magic based on the controller action parameters and the names used in the form. It basically maps the values in the form to a bean that is used as the third parameter in the action method.
For example my SomeBean has some fields named byday and bymonth. It also has the corresponding byday and bymonth setters and getters (i.e. getBymonth(), setBymonth). In my for my submit action is mapped on submit and I have input values for byday and by month like so:
<select id="weekly_option" name="byday">
<option value="MON">Monday</option>
<option value="TUE">Tuesday</option>
<option value="WED">Wednesday</option>
<option value="THU">Thursday</option>
<option value="FRI">Friday</option>
<option value="SAT">Saturday</option>
<option value="SUN">Sunday</option>
</select>
I had to do some digging on how exactly the mappings were being done. I peeked into the MultiActionController source code to see that if does the following:
The controller figures out if you have a third parameter in your action (it must not be of the type HttpSession).
The MultiActionController then news up an instance of the third parameter (SomeBean). Based on the http request values it pushes over all the values from the HttpServleRequest over to the SomeBean object.
At this point it seems like it only works with properties that are strings. I imagine that you would have to extend MVC somehow if you wanted to work with properties other than strings within your bean.