@Pattern (javax.validation)
The @javax.validation.constraints.Pattern annotation is recognized by Apache Causeway as a means to specify a regular expression constraint for properties and action parameters of type java.lang.String.
For example, here’s the annotation being used on an action parameter:
public Customer updateName(
                    @javax.validation.constraints.Pattern(
                        regexp="[A-Z].+"
                        message="Must begin with a capital."
                    )
                    final String name) {
    setName(name);
    return this
}
...
and here’s an example of its use on a property:
@javax.validation.constraints.Pattern(
    regexp="[A-Z].+"
    message="Must begin with a capital."
)
public String getName() {
    return name;
}
...
For properties, it is also possible to specify against a field if Lombok is being used:
import javax.validation.constraints.Pattern;
import lombok.Getter;
import lombok.Setter;
@Pattern(
    regexp="[A-Z].+"
    message="Must begin with a capital."
)
@Getter @Setter
private String name;