Spring Validation - BindingResult

Question

I am trying to understand what BeanPropertyBindingResult does in the following code. Unfortunately, the javadoc is quite useless.

Please take a look at the following code:

BeanPropertyBindingResult errors = new BeanPropertyBindingResult(item, "item");
validator.validate(item, errors);

My questions are:

1. As far as I can see, BeanPropertyBindingResult is basically some kind of a Map that can contain key/value pairs of (field name, error text). Is this correct, or is the truth more complicated?

2. When I create a new BeanPropertyBindingResult, why do I need to provide it (as the constructor's first parameter) with the object I am going to validate? As far as I can see, in the second line above, validator.validate(item, errors); the validator gets the object anyway.. so why doing it twice?

3. The javadoc says about the constructor's second parameter:

objectName - the name of the target object

yes, but why do I need that name? What am I supposed/able to do with it...?

Answer 1

1) Yes, that is my understanding too, even if it is technically a list. -- The most importent part is List<ObjectError> errors defined in the superclass AbstractBindingResult.

2) Because it is demanded by the BindingResult Interface. -- I know this is not a good answer, but If this interfaces requires that method, then ther is no otherway to implement it BTW: I think I have seen some example before where the Autor used null for that field, but I am not 100% if it works correct, but most of the code seams to be able to handle the null value.

3) If you use that binding result for example in a jsp to show the error messages for different input fields, then this must match the model attribute name.

Assume you have a command object with a field name. And a JSP page where the input filed is associated to myCommand.name. Then you need the name myCommand as some kind of prefix for the binding errors. -- It is hard to explain, I hope you understand what I mean