Adding @NotNull or Pattern constraints on List

Question

How can we ensure the individual strings inside a list are not null/blank or follow a specific pattern

@NotNull
List emailIds;

Answer 1

You can create a simple wrapper class for the e-mail String:

public class EmailAddress {

    @Pattern("\b[A-Z0-9._%+-]+@[A-Z0-9.-]+.[A-Z]{2,4}\b.")
    String email;

    //getters and setters
}

Then mark the field @Valid in your existing object:

@NotNull
@Valid
List emailIds;

The validator will then validate each object in the list.