validating that a field is unique using Bean Validation (or JSF)

I have an simple object that has a name

public class Foo {

    private String name

}

Each user on the site may have up to 10 Foo's associated with them. Within this context, when a new Foo is created, I would like to validate that there isn't another foo associated with the same user that already exists.

I could Create a custom Bean Validator But annotations require the paramaeters to be defined during compilation. How would I then pass across the names of the existing Foos?

As suggested in various places, I could use EL expressions as an alternative way to pick up the data. This feels like using a sledgehammer to crack a nut. It also brings in a whole bunch of potential issues to consider least of all being ease of testing.

I could do class-wide validation using a boolean field

@AssertTrue(message="Name already exists")
public boolean isNameUnique() {
    return (existingNames.contains(name));
}

But the validation message would not show up next to the name field. It is a cosmetic issue and this can be a backup plan. However, its not ideal.

Which brings me to the question:

Is there a simple way to write a Bean Validator that can check the value against a collection of values at the field level and meet the following restrictions ?

Previous values determined at runtime
Not using things like EL expressions
Field level validation instead of class level.

EDIT in reponse to Hardy:

The Foo class is an entity persisted within a database. They are picked up and used through a DAO interface.

I could loop through the entities but that means plugging the DAO into the validator and not to mention that the I would need to write the same thing again if I have another class that too has this constraint.

Solution

It would help to see how you want to use the Foo class. Can you extend your example code? Are they kept in a list of Foo instances. A custom constraint seems to be a good fit. Why do you need to pass any parameters to the constraints. I would just iterate over the foos and check whether the names are unique.