Binding Custom Object to Collection

[jbriscoe]

I have read many posts on this subject however, I have yet to see a solution to the problem. How do I bind an indexed property of ArrayList type with a custom object that contains properties I need set? I have found most developers bind to a single property but, I need the flexiblity to set multiple properties on my model object.

For example...

I have a FormAction that contains a model object in flow scope; Address which looks like this:

public class Address {
	private String address1;
	private String address2;
	private String city;
	private String state;
	private Integer zip;
	private ArrayList<Resident> residents = new ArrayList<Resident>();
... All Getters & Setters here...

The Resident class looks like this:

public class Resident {
	private String firstName;
	private String lastName;
... All Getters & Setters here...

Application context (address.xml) looks like this:

	<bean id="addressFormAction"
		class="org.springframework.webflow.action.FormAction">
		<property name="formObjectName" value="address" />
		<property name="formObjectClass"
			value="com.briskoe.model.Address" />
		<property name="formObjectScope" value="FLOW" />
	</bean>

My flow definition looks like this:

<flow start-state="showNewAddressForm">

	<view-state id="showNewAddressForm" view="addressForm">
		<entry-actions>
			<action bean="addressFormAction" method="setupForm"/>
		</entry-actions>
		<transition to="confirmAddressChange" on="submit">
			<action bean="addressFormAction" method="bind" />
		</transition>
	</view-state>

	<view-state id="confirmAddressChange"
		view="confirmAddressChangeForm">
		<transition to="complete" on="submit" />
	</view-state>

	<end-state id="complete" view="thankYou" />

	<import resource="address.xml"/>

</flow>

I am executing this flow through a test case which looks like this:
public class AddressFlowTest extends AbstractXmlFlowExecutionTests {

	@Override
	protected ExternalizedFlowDefinition getFlowDefinition() {
		return new ExternalizedFlowDefinition("address-flow",
				new ClassPathResource("com/briskoe/address-flow.xml"));
	}

	public void testAddressFlow() {
		final ApplicationView appView = (ApplicationView) startFlow();
		assertCurrentStateEquals("showNewAddressForm");

		final HashMap formData = new HashMap();
		formData.put("address1", "1 Infinite Loop");
		formData.put("address2", "Suite 200");
		formData.put("city", "Cupertino");
		formData.put("state", "CA");
		formData.put("zip", "90210");

		formData.put("residents[0].firstName", "Apple");

		signalEvent("submit", new ParameterMap(formData));

		assertCurrentStateEquals("confirmAddressChange");

		assertModelAttributeNotNull("address", appView);

		final Address address = (Address)appView.getModel().get("address");
		assertEquals(1, address.getResidents().size());
	}
}

The test case fails on signalEvent("submit"...) complaining about an Index Out of Bounds, which I suspected was caused by the binding not occurring correctly:

org.springframework.webflow.ActionExecutionException: Exception thrown executing [AnnotatedAction@1c74f37 targetAction = org.springframework.webflow.action.FormAction@641e9a, attributes = map['method' -> 'bind']] in state 'showNewAddressForm' of flow 'address-flow' -- action execution properties where 'map['method' -> 'bind']'; nested exception is org.springframework.beans.InvalidPropertyException: Invalid property 'residents[0]' of bean class [com.briskoe.model.Address]: Index of out of bounds in property path 'residents[0]'; nested exception is java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
Caused by: org.springframework.beans.InvalidPropertyException: Invalid property 'residents[0]' of bean class [com.briskoe.model.Address]: Index of out of bounds in property path 'residents[0]'; nested exception is java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
Caused by: java.lang.IndexOutOfBoundsException: Index: 0, Size: 0

Has anyone tried to accomplish what I am and if so how did you do it?

[jbriscoe]

Finally! I have a solution to this problem... I was inspired by this comment: http://maas-frensch.com/peter/2006/0...estdatabinder/ . So, leveraging the Common's Collections ListUtils class I am able to give spring the ability to generate ArrayList entries on-demand. When Spring instantiates my Address class which is my Form backed bean, it uses my no-arg constructor. Knowing that, I added this bit of code to the constructor:

residents = ListUtils.lazyList(new ArrayList<Resident>(), FactoryUtils.instantiateFactory(Resident.class));

Then I updated my field within the Address class to be a null reference:
private List<Resident> residents;

Wow! It actually works now if I do things like this in my unit-tests:

		final ApplicationView appView = (ApplicationView) startFlow();
		assertCurrentStateEquals("showNewAddressForm");

		final HashMap formData = new HashMap();
		formData.put("address1", "1 Infinite Loop");
		formData.put("address2", "Suite 200");
		formData.put("city", "Cupertino");
		formData.put("state", "CA");
		formData.put("zip", "90210");

		formData.put("residents[0].firstName", "Foo");
		formData.put("residents[0].lastName", "Bar");

		formData.put("residents[1].firstName", "Red");
		formData.put("residents[1].lastName", "Talorway");

		signalEvent("submit", new ParameterMap(formData));

		assertCurrentStateEquals("confirmAddressChange");

		assertModelAttributeNotNull("address", appView);

		final Address address = (Address) appView.getModel().get("address");
		assertEquals(2, address.getResidents().size());

I hope this helps someone.

[sre786]

Thanks for the solution. It works fine for the collections. But how do we handle the custom objects inside the collections. For example
I have a form where I am collecting dependents for an insurer. Say there could zero to 10 dependents. So I have 10 optional field groups on my form each field group corresponding to one dependent entry

I have a collection person objects. 
Person 
- Name 
   - First Name
   - Last Name 
- Age 

In my velocity template file I would refer to them as 
#springFormInput("Insured.dependent[0].name" "class=dis maxlength=128")
#springFormInput("Insured.dependent[0].age" "")

I have custom property editor to convert user input to Name object. And my form backing object has a collection of dependents (person objects).

I can lazy initialize persons ArrayList but for each person instantiated I would have to pre-initialize the Name instance in its constructor. Is there a better solution for this?

I have seen another thread
http://forum.springframework.org/showthread.php?t=22015

where it is mentioned to use

binder.setIgnoreInvalidFields(true); 

and test for null in the view like 

<c:if test="${target.address eq null}"><input name="address.city" value="" /></c:if>
<c:if test="${target.address ne null}"><form:input path="address.city"/></c:if>

I feel that its kind of ugly to have bunch of null checks in the JSP/vm file to solve this issue. Any good solution for this issue?

[rafaricoc]

I hope this helps someone.

Thanks a lot for the solution, I had like a day trying to figure it out why. until I found your post.

thnx!