Dynamic list binding in Spring MVC

I'm having problems dynamically adding rows via JavaScript and gett Spring to handle it correctly. I can't tell if your solution solves this problem. Based on what you have listed under Problem 1, it sounds like it might, but I can't tell. If this does solve that particular problem, did you have to do anything more than simply add the row via JavaScript? I've seen some references to registering custom binders, but I've tried that as well and it doesn't seem to work.

Using the commons collections LazyList worked, it got rid of the ArrayIndexOutOfBoundsException. However, I don't understand why the added element isn't there when binding, but it is there by the time it gets to the onSubmit() method of the Controller.

I am pretty new to doing forms dynamically in HTML and with Spring. I am not clear where you put the "real" unhidden text fields for the table -- where you would enter the data values. Is there a correlated JavaScript that goes along with this example. A full example would go a long way to help my understanding of the topic.

I guess what I'm not clear on is why the input type is "hidden" in the .jsp snippet, and how real "text" input types get bound to these "hidden" types that get bound by spring to the BindStatus object.

I understand the concept of indexing the elements through c:forEach, so they can be picked up and bound by Spring, just not sure where the rubber meets the road on this one.

Any help anyone can provide would be great! I'm perplexed.

Hi,

I am new in the Spring Framework and I tried very hard to find a dynamic forms example. This is the only one I am able to google. The example as it is already answered some questions for me. But I still have a couple of questions. For example, why did you not have a showForm() method? Did you not need one, or did you just not post it because you thought it is trivial? Also, I'd be very interested in seeing how you wire the beans in your servlet.xml. I wonder if you can post the entire source code so I can compile and play with the deployment. I'd greatly appreciate it if you can do so.

Again, I am new here and I care more about how to make dynamic forms work as opposed to how to make them work efficiently, which seems to be what you focused on in this example. It will help me greatly as well if you could point me to a complete example of dynamic forms.

Thanks for your help in advance!

-lpanl

Hi Matt:

Thanks for your advice! I have gone through the path of making
it very simple to find out a couple of bugs and then coming
back to the full functionality using dynamic forms and checkboxes
and luckily I now made it work.

One question I have now is that I observed that the
test if (!isFormSubmission(request)) is always true
whether I direct the successView to be a new htm
or to come back to the same view. As a result,
I did not need to use the LazyList and every
single formBackingObject call is going to hit
the DB and generate the catalog (expensive to call).

So my question is: in what situation the test
isFormSubmission(request) is ever true?
My code is listed below.

Thanks a lot!

-lpanl

protected Object formBackingObject(HttpServletRequest request)
throws ServletException {

Catalog catalog = null;

logger.info("CCCC===== StreamliningController.formBackingObject called !");

if (!isFormSubmission(request)) {
catalog = cm.getCatalog();
}
else
logger.info("^^^^^^^^^^^^ StreamliningController isFormSubmission!");

return catalog;
}

Hi,
Although the LazyList works for me, I do not know why. I am using the new spring:form tags and the form submission worked well for me with a lazylist. The problem I am having now is since the object instantiation is in the hands of the framework when we submit the form, I have to specify a concrete class name in the FactoryUtils.instantiateFactory() method. How do I get around this problem if I have an abstract class and on runtime I need to pass an inherited class object to the instantiateFactory method. So I have :

private List baseList = LazyList.decorate(new ArrayList(), FactoryUtils.instantiateFactory(Inherited1.class));

So now I want to be able to decide which class to pass Inherited1.class or Inherited2.class. How and on which callback method can I do that?

Is this the sequence diagram, although this is a not at all sequence diagram, that you were looking for??

http://mikenereson.blogspot.com/2007/02/spring-mvc-controller-processing.html

I used a similar method for your list binding.
Here is my question.
I have a list in my command bean.
When I click add phone on my page I dynamically generate the input for the phone number. I can add as many as I want.
When I submit Spring binds it to the collection like you have. Even if I go into an error and the form is invalid the phone numbers I have come back populated. The issue I have is if I click a javascript link to remove the input field and then go onsubmit it does not "rebind" what is visible since what I have in the list is still there. I am doing this as I sit on the form with errors. Say I fogot to input a name. Well if at that point I decide to remove a phone and input a name that form then passes validation but it still binds two phone numbers not one.

I tried clearing the list on the init binder but that did not work.

I am trying to figure a way to dynamically through javascript be able to remove the input fields and then have the form rebind the visible ones.

The issues with the removing is only happening when I come back from a error onvalidating.

Ideas..
Thanks.

Great tutorial here ...

I work with the petclinc example. And in this example the Controller works with the methods setupForm and processSubmit. No formBackingObject or onSubmit - no Command object ... and so on.

In the JSP the petclinic example works with form:form modelAttribute="..." and form:input path="...".

In the examples with the dynamic list there works with spring:bind path="...".

So ... i am not sure wheter the solutions works also for "my" controllers and jsp's I hope so ... but i am not sure.

Or is it possible to "translate" the solutions into "my way to display a form to the user" ?!? When this is possible it's easier to me when i have an example.

Many Greetings,
Oliver

Hi Matt and everyone,

Trying the solution above because it looks quite elegant.

I have LazyList similar to your example (Grid):

	private List items = ListUtils.lazyList(new ArrayList(), 
			new Factory(){
        public Object create(){
            return new Item();
        }
        });

In my JSP I display one extra item (new item to be created and persisted) when looping through the list. My understanding that LazyList should allow this, right?

But when the JSP is displayed for the first time (not the submission part), I still get IndexOutOfBoundsException exception:

java.lang.IndexOutOfBoundsException: Index: 1, Size: 1
	at java.util.ArrayList.RangeCheck(Unknown Source)
	at java.util.ArrayList.get(Unknown Source)
	at org.hibernate.collection.PersistentList.get(PersistentList.java:271)
	at org.springframework.beans.BeanWrapperImpl.getPropertyValue(BeanWrapperImpl.java:556)
	at org.springframework.beans.BeanWrapperImpl.getNestedBeanWrapper(BeanWrapperImpl.java:441)
	at org.springframework.beans.BeanWrapperImpl.getBeanWrapperForPropertyPath(BeanWrapperImpl.java:418)
	at org.springframework.beans.BeanWrapperImpl.getPropertyValue(BeanWrapperImpl.java:524)
	at org.springframework.validation.AbstractPropertyBindingResult.getActualFieldValue(AbstractPropertyBindingResult.java:77)
	at org.springframework.validation.AbstractBindingResult.getFieldValue(AbstractBindingResult.java:337)
	at org.springframework.web.servlet.support.BindStatus.<init>(BindStatus.java:117)
	at org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.getBindStatus(AbstractDataBoundFormElementTag.java:179)

Am I missing something simple?

Thanks!

Dima

Thanks, Matt.

After a bit of debugging, I think I figured it out:

The object that contains the list in question is persisted by Hibernate. Hibernate was replacing the list with PersistentList.

I might have to use some intermediary command object or find other way to get the new item in.

Cheers,

Dima

The LazyList works great, I didn't know about that.
I am using Spring MVC 2.5.1 and the @ModelAttribute annotation on my form Object that holds the list.

Cheers
----
PLATOGO - play together online

Hi, Matt -

Thanks for posting this. It and the additional questions/comments helped tremendously. I have things working for a page in my app just fine. But I would like to use a textarea rather than some flavor of input as I need multiple lines; I have it working using input / text right now. Since textarea does not have a value attribute, no data is displayed. Is there a way to implement this solution for a textarea?

Thanks,

Bill

hi Matt,

I have a RefreshablePagedListHolder with a list of user details. the list is displayed with paging capabilities in a jsp page. i have included a checkbox to select the necessary users (a checkbox for each user) and bound them as u showed above. my controller is a MultiActionController as i have to handle paging requests as well as the submit request where i have to remove the users selected by the checkboxes.
when using MultiActionController i have to set a url parameter specifying the method to be invoked so i set the window.location at the onclick event of the submit button.

however, the checkbox values are not bound to the bean when the method at the controller is invoked. but the returning bean shows that the previously checked checkboxes as checked. this means that although the spring binding does not occur at the time of the method invocation, the changes made are retained after the processing of the request.

so as i understand, if x is the sequence of method invocation, the changes made at x is actually carried out at the (x + 1)th request.

hope u got my problem clearly. i have been struggling with this problem for a long time and still cudn find a solution. hope u can help me solve this.

thanx in advance

Gayani

I just did a work-around for the problem. I am checking whether a submission has occured when the page loads and if it is a response to a submission, I am reloading the page. This way I can avoid the problem. However I'm very keen to find what went wrong where in my coding.

Hej
Great article, you helped me make some positive steps in the right direction. I've come across some problems binding my items and getting em back into my class though.

the jsp I'm using is very similar:

<c:forEach var="param" items="command.advParams" varStatus="rowItem">
<span id="multi_search_fields">
	<c:set var="actual" value="${rowItem.index}"></c:set>
	<!-- Field types -->
	<spring:bind path="command.advParams[${rowItem.index}].field">
  		<select name="advParams[${rowItem.index}].field" id="additional_multi_search_field_${rowItem.index}"  onChange="updateOperators(this)">
			<c:forEach var="searchField" items="${command.searchFieldList}">	
				<option <c:if test="${searchField.name == status.value}">selected</c:if> value="${searchField.name}">
					<c:out value="${searchField.display}" />
				</option>
			</c:forEach>		
		</select>
	</spring:bind>
 
	<!-- Operators -->
  		<select name="advParams[${rowItem.index}].operator" id="additional_search_operator_${rowItem.index}" >
		</select>
 
	<!-- Keywords -->
	<spring:bind path="command.advParams[${rowItem.index}].keyword">
  		<input type="text" name="advParams[${rowItem.index}].keyword" value="<c:out value='${status.value}'/>"
			id="additional_multi_search_value_${rowItem.index}"  onkeydown="doOnEnter(event,submitSearch);"/>
  	</spring:bind>
</span>
</c:forEach>

I think I've got my collection set up right... The following is part of my SearchFormImpl class which gets set in the onSubmit of my SimpleFormController: searchFormImpl = (SearchFormImpl)command;

	private Collection<AdvancedSearchParam> advParams;
 
	public void setAdvParams(Collection<AdvancedSearchParam> advParams) {
		this.advParams = advParams;
	}
	public Collection<AdvancedSearchParam> getAdvParams() {
		return advParams;
	}

<c:forEach var="param" items="command.advParams" varStatus="rowItem">
<span id="multi_search_fields">
	<c:set var="actual" value="${rowItem.index}"></c:set>
 
row: <c:out value="${rowItem.index}" /> 
field: <c:out value="${param}" /> <br/>
 
	<!-- Field types -->
	<spring:bind path="command.advParams[${rowItem.index}].field">
.......

row: 0 field: {advParams[0].field=content, advParams[0].keyword=test, advParams[1].field=docdatetime, advParams[1].keyword=wef, advParams[1].operator==, advParams[0].operator==} 

Any thoughts???

I think your problem is that you are specifying the wrong name attributes for the actual html elements within the bind tag. It is the name attribute that is used by Spring MVC to do the binding.

E.g

<spring:bind path="command.advParams[${rowItem.index}].keyword">
  	<input type="text" name="advParams[${rowItem.index}].keyword" value="<c:out value='${status.value}'/>"
		id="additional_multi_search_value_${rowItem.index}"  onkeydown="doOnEnter(event,submitSearch);"/>
</spring:bind>

Should be

<spring:bind path="command.advParams[${rowItem.index}].keyword">
  	<input type="text" name="${status.expression}" value="${status.value}"
		id="additional_multi_search_value_${rowItem.index}"  onkeydown="doOnEnter(event,submitSearch);"/>
</spring:bind>

I'm not sure which version of jstl you are using but you probably don't need the c:out tags either, if you do just add them around the status.xxx calls.

-Matt

Look at the html that is output. You should see something like formBackingObjectName.listName[##].property in the name attribute for the html element. If you don't see that, spring mvc won't bind it. If that doesn't lead me anywhere, the other thing that I do is turn on more verbose logging in the spring mvc components. There is binding debug statements.

I think sometimes we get a little lost in the trees on this kind of stuff and make the data binding process more complicated than it really is, though. You should be able to make your own static html page with the form elements you want to bind and submit it. Spring MVC is really easy to use once the data binding mechanism is truly understood. I'd suggest you creating a simple prototype application where you can experiment with standard data types and then get into your own custom data types to fully understand the process... it sounds like that's what you're going to do...

-Matt