Why do I get this error when specifying a parameter from the URL?

Question

Hello,
I am trying to "install" a parameter in a page, so that it's value can be specified in the URL and a VO updated according to this value.
Here's is the page definition file, with an executable and a binding to a method call:
<executables>
<invokeAction Binds="prepareMainMenuView1" id="invokeQuery"
Refresh="prepareModel"/>
</executables>
<methodAction id="prepareMainMenuView1"
InstanceName="AppModuleDataControl.dataProvider"
DataControl="AppModuleDataControl" RequiresUpdateModel="true"
Action="invokeMethod" MethodName="prepareMainMenuView1"
IsViewObjectMethod="true">
<NamedData NDName="param" NDValue="#{param.root_menu}"
NDType="java.lang.String"/>
</methodAction>
if I run the MyMenu application with:
http://127.0.0.1:7101/MyMenu-ViewController-context-root/faces/menu?root_menu=anything
then I get this exception:
ADF: Adding the following JSF error message: String index out of range: -1
java.lang.StringIndexOutOfBoundsException: String index out of range: -1
Do you know why? Where do I fail?
I followed the isntruction here:
http://www.jasonsdevelopercorner.com/?p=65
So far I have not been able to read a parameter in a way, do you have any example on how can I use parameters from URL from within a single page in an unbounded task flow?
I worked all the day on this, but with no luck.
Thanks

Answer 1

I solved the problem. The invoked method was not part of the VO, but was part of the AM.