JSF java.util. Concurrent ModificationException

[Dennis Black]

So I know what my problem is, I just don't know how to get around it.

I have a shopcart that allows the user to update quantity, pretty straightfoward.

<h:form >
<h ataTable var="item" value="#{shopCartBean.orderItems}">
<h:column>
<f:facet name="header">
<h utputText value="Product"/>
</f:facet>
<h utputText value="#{item.productName}"/>
</h:column>
<h:column>
<f:facet name="header">
<h utputText value="Price"/>
</f:facet>
<h utputText value="#{item.unitPrice}"/>
</h:column>
<h:column>
<f:facet name="header">
<h utputText value="quantity"/>
</f:facet>
<h:inputText value="#{item.quantity}" required="true" />
</h:column>
<h:column>
<f:facet name="header">
<h utputText value="Total"/>
</f:facet>
<h utputText value="#{item.totalPrice}" />
</h:column>
</h ataTable>
<h:commandButton value="update" action="#{shopCartBean.updateCart}" />
</h:form>

Problem is, if they update the quantity to zero, I want to take that item out of the cart. So I do it like this...

public String updateCart() {
Iterator it = orderItems.iterator();
while (it.hasNext()) {
OrderItem oi = (OrderItem) it.next();
if (oi.getQuantity() == 0)
orderItems.remove(oi);
}
return "review";
}

Which throws a java. util. Concurrent ModificationException I gather because JSF is messing with the list while I'm removing it. I made orderItems a synchronizedList, didn't help at all.

Any ideas for a work around?

Thanks,
Dennis
[ February 27, 2006: Message edited by: Dennis Black ]

[Peter Goldstein]

Why don't you make a new List that is a copy of the old one, remove the item from the copy, and set the new List in the bean? I think that should work as a workaround.

[Dennis Black]

Peter I thought you had the solution for sure. I was even doing the guinness guys "Brilliant" in my head.

But it didn't work Same error.


public String updateCart() {
List newOrderItems = new ArrayList(this.orderItems);
Iterator it = newOrderItems.iterator();
while (it.hasNext()) {
OrderItem i = (OrderItem) it.next();
if (i.getQuantity() < 1)
newOrderItems.remove(i);
}
this.orderItems = newOrderItems;
return "review";
}

[Dennis Black]

Well here is my solution. I wish I could say it's the cheesiest thing I've done since I started using JSF, but it's not even in the top 10.

<h:dataTable var="item" value="#{shopCartBean.orderItems}">
<h:column>
<f:facet name="header">
<h:outputText value="Product"/>
</f:facet>
<h:outputText value="#{item.productName}" rendered="#{item.quantity >= 1}" />
</h:column>
<h:column>
<f:facet name="header">
<h:outputText value="Price"/>
</f:facet>
<h:outputText value="#{item.unitPrice}" rendered="#{item.quantity >= 1}"/>
</h:column>
<h:column>
<f:facet name="header">
<h:outputText value="quantity"/>
</f:facet>
<h:inputText value="#{item.quantity}" rendered="#{item.quantity >= 1}" required="true" />
</h:column>
<h:column>
<f:facet name="header">
<h:outputText value="Total"/>
</f:facet>
<h:outputText value="#{item.totalPrice}" rendered="#{item.quantity >= 1}" />
</h:column>
</h:dataTable>

[Peter Goldstein]

Dennis, I didn't look closely enough at your original post. I don't think the problem is that JSF is doing something with the list, it's that you've got an open Iterator and are using the Collection methods rather than Iterator methods to remove the item.

Try replacing otherItems.remove(o) with it.remove(o) in your original solution. That may very well solve your problem.

That would explain why you're encountering the same problem with the copied List, which the underlying code can't be manipulating.

[Dennis Black]

Peter, Thanks much. Total noobar mistake on my part.