gistfile1.java

@Config(desc = "A binary tree")
@BinaryTreeConstraint
public class BinaryTree {
    @Id(desc = "id of current node")
    private String id;

    @Config(desc = "value of current node")
    @NotNull @Min(1)
    private Integer value;

    @Config(desc = "left child")
    private BinaryTree left;

    @Config(desc = "right child")
    private BinaryTree right;

    public Integer getValue() { return value; }
    public BinaryTree getLeft() { return left; }
    public BinaryTree getRight() { return right; }
    public String toString() { return id + "=" + value; }
}

public class BinaryTreeValidator implements 
    ConstraintValidator<BinaryTreeConstraint, BinaryTree> {

    public boolean isValid(BinaryTree n, ConstraintValidatorContext c) {
        if (n.getLeft() != null && n.getValue() < n.getLeft().getValue()) {
            String msg = n.getLeft() + " must be to right of " + n;
            c.buildConstraintViolationWithTemplate(msg).addConstraintViolation();
            return false;
        }
        if (n.getRight() != null && n.getValue() > n.getRight().getValue()) {
            String msg = n.getRight() + " must be to left of " + n;
            c.buildConstraintViolationWithTemplate(msg).addConstraintViolation();
            return false;
        }
        return true;
    }

    public void initialize(BinaryTreeConstraint constraintAnnotation) { }
}

@Target({ TYPE })
@Retention(RetentionPolicy.RUNTIME)
@Constraint(validatedBy = BinaryTreeValidator.class)
public @interface BinaryTreeConstraint {
    String message() default "";
    Class<?>[] groups() default {};
    Class<? extends Payload>[] payload() default {};
}