Populating a dropdown based on previous dropdown selection

Hi

I am using WebDynpro for Java with adobe interactive elements. On abobe form I have 4 dropdowns. I am able to populate the first dropdown values from a adaptive webservice model using context mapping and some coding. But values in second drop down depends on first dropdown selection. So on first dropdown when user selects a value, I should call a method in webdynpro, this method will make a webservice call, this will return the values for second dropdown. Here I am not sure about how to call a webdynpro java method from adobe event. Please suggest me on how to do this.

Thanks

Praveen