Why does Hibernate Validator @NotEmpty produce duplicate messages?

Question

While working with Hibernate Validator, I noticed that the @NotEmpty and @NotNull annotations produce duplicate messages in the InvalidValue array returned by getInvalidValues(...).

If I specify a message like @NotEmpty(message = "My error message."), then I'll get one InvalidValue of "My error message." and a second of "may not be null or empty"

If i don't include a message (eg @NotEmpty by itself), then I get two copies of the InvalidValue with a message field of "may not be null or empty".

Why does Hibernate Validator do this?? Shouldn't I get one message, either the value that I override using the parameter, or the default message, but not both??

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For some more context:

I am extending ClassValidator<T> with my own ClassValidator<MyClass> implementation. I do so to add some custom validations which cannot be done by annotation. I need to see the run time value of more than one property of the class in order to determine the validation.

I get the validations when I call myClassValidator.getInvalidValues(), which I override. Inside my implementation of getInvalidValues() I call super.getInvalidValues() to create the initial error list, and then I add my custom errors to that list. In any case, the call to super.getInvalidValues() contains the duplicate messages, one matching the message property passed into the annotation, and a second with the stock value of the annotation message.

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Answer 1

Justin,

I've been working with Hibernate Validator for the last couple of months. While I have not run into the same issue that you've described, I also have not extended ClassValidator. For custom validation, the Hibernate Reference Guide indicates that writing custom constraints is the way to go.

I have been able to use the built-in constraints almost exclusively on my current project. In one case, where I needed to do some very specific calculations on an integer field, I wrote a custom constraint as described in the reference guide; it was a breeze.

Speaking to your specific problem, I wrote a simple test app as a sort of sanity check on my part:

import org.hibernate.validator.*;

public class HibernateValidatorTest {
    @NotEmpty
    @NotNull
    private String validateMe;

    public static void main ( String[] args ) {
     ClassValidator<HibernateValidatorTest> validator = 
      new ClassValidator<HibernateValidatorTest>( HibernateValidatorTest.class ); 

     InvalidValue[] inVals = 
      validator.getInvalidValues( new HibernateValidatorTest() );

     for ( InvalidValue inVal : inVals ) {
      System.out.println( inVal.getMessage() );
     }
    }
}

With both Hibernate constraints on the validateMe field, the console output is:

may not be null or empty
may not be null

Removing one or the other has the expected effect of printing only a single message to the console.

I hope this is helpful.

Brian T. Grant