How can i call a business model function?

Question

Hello!
I have a simple problem
A gui view-backing - function call the setUsername by FacesContext und operative Buinding - it works well.
Now i want to call the the function getUsername from a function inside the class EntityImplEx - both classes are in the business model in different class-pathes.
How can I call the function getUsername from AppModule?
package model.app;
public class AppModuleImpl extends ApplicationModuleImpl implements AppModule {
    public String username                = "init";
    public void setUsername(String ss) {
        username=ss;
    public String getUsername() {
        return(username);
package model.entity;
public class EntityImplEx extends EntityImpl {
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Answer 1

You probably don't want to call a function in your UI from your AM.
Doing this will break the MVC design pattern and will make your AM depends on a specific UI page.
The way to communicate between the two is through service methods on the AM that are invoked from the UI layer.
See chapters 8.3-8.5 in the developer guide:
http://download.oracle.com/docs/html/B25947_01/bcservices003.htm#sm0206