Java – use generics in parameters of exceptions

I'm trying to store a collection of generic objects in exceptions and have trouble figuring out generics Specifically, I am using hibernate validator and want to save the collected violation list in the exception for processing in another layer of application Here is an example:

Set<ConstraintViolation<User>> violations = validator.validate(user);
if (violations.size() > 0) {
    throw new ValidationException("User details are invalid",violations);
}

In eclipse, the throws line shows that the constructor is undefined and suggests that I change the constructor signature to validationexception (string, set & constraintviolation < user > > > here is validationexception:

public class ValidationException extends Exception {
    private Set<ConstraintViolation<?>> violations;

    public ValidationException() {
    }
    public ValidationException(String msg) {
        super(msg);
    }
    public ValidationException(String msg,Throwable cause) {
        super(msg,cause);
    }
    public ValidationException(String msg,Set<ConstraintViolation<?>> violations) {
        super(msg);
        this.violations = violations;
    }
    public Set<ConstraintViolation<?>> getViolations() {
        return violations;
    }
}

However, I want to keep the validationexception generic so that I can use it more than just user authentication I tried set < < constraintviolation > and get the same result

Is there any way to accomplish what I want to do?

Solution

You need to declare the violation setting parameter as set

public ValidationException(String msg,Set<? extends ConstraintViolation<?>> violations) {
  super(msg);
  this.violations = Collections.unmodifiableSet(
      new HashSet<ConstraintViolation<?>>(violations));
}

Then everything should work as expected

This has the additional benefit of defensive replication, ensuring that the inner set of exceptions cannot be changed