Cross field validation with Hibernate Validator (JSR 303)

Question

Is there an implementation of (or third-party implementation for) cross field validation in Hibernate Validator 4.x? If not, what is the cleanest way to implement a cross fi

Answer 1

I like the idea from Jakub Jirutka to use Spring Expression Language. If you don't want to add another library/dependency (assuming that you already use Spring), here is a simplified implementation of his idea.

The constraint:

@Constraint(validatedBy=ExpressionAssertValidator.class)
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
public @interface ExpressionAssert {
    String message() default "expression must evaluate to true";
    Class[] groups() default {};
    Class[] payload() default {};
    String value();
}

The validator:

public class ExpressionAssertValidator implements ConstraintValidator {
    private Expression exp;

    public void initialize(ExpressionAssert annotation) {
        ExpressionParser parser = new SpelExpressionParser();
        exp = parser.parseExpression(annotation.value());
    }

    public boolean isValid(Object value, ConstraintValidatorContext context) {
        return exp.getValue(value, Boolean.class);
    }
}

Apply like this:

@ExpressionAssert(value="pass == passVerify", message="passwords must be same")
public class MyBean {
    @Size(min=6, max=50)
    private String pass;
    private String passVerify;
}