My custom event handler does not show the warning in IOM interface

Hi all! 

I wrote a custom Event Handler that implements "ValidationHandler." After carrying out a check on the OIM database, if the class detects a problem, throw an exception of "ValidationFailedException" and it must show the warning on the screen IOM. That way I can block the user who wants to do the operation is not permitted. My code is as follows:

public class HandlerConQuery implements ValidationHandler {

    

    private String chiaveUtente;

    

    public void validate(long l, long l1, Orchestration orchestration) {

        

        try{

            Connection connessione = <method to connect to OIM db>  

            

            chiaveUtente = ContextManager.getUserPreference("usr_key").toString();

            

            HashMap<String, Serializable> parameters = orchestration.getParameters();