spring mvc validation best practices

Question

I am learning myself Spring MVC 2.5 mostly from the docs. Can someone explain the following:

Advantages/differences of using command objects versus using @ModelAttribute to pass in the object.
Is there an easier way to do validation other then writing a Validator object?

Also, in this code how does the line ValidationUtils.rejectIfEmpty(e, "name", "name.empty"); work? How can it check if the name is empty on the person object when the person object is not passed in?

   public void validate(Object obj, Errors e) {
        ValidationUtils.rejectIfEmpty(e, "name", "name.empty");
        Person p = (Person) obj;
        if (p.getAge() < 0) {
            e.rejectValue("age", "negativevalue");
        } else if (p.getAge() > 110) {
            e.rejectValue("age", "too.darn.old");
        }
    }

(this code is from section 5.2 from the docs)

Thanks

axtavt · Accepted Answer · 2010-12-30 17:55:58Z

3

The question about command object is not very clear. If you mean the following syntax
```
@RequestMapping(...) public ModelAndView foo(Command c) { ... }
```
then it is the same as the following
```
@RequestMapping(...) public ModelAndView foo(@ModelAttribute Command c) { ... }
```
because @ModelAttribute can be omitted. The only case when it's actually needed is then you need to specify attribute name explicitly (otherwise it would be inferred as a class name with the first letter decapitalized, i.e. command)
In Spring 2.5 - no. In Spring 3.0 you can use declarative validation with JSR-303 Bean Validation API.
The Errors object has a reference to the object being validated.

answered Dec 30, 2010 at 17:55

axtavt

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2 Comments

mkoryak Over a year ago

I guess my understanding of command object isnt clear. I thought that with @ModelAttribute you could annotate an object that will contain properties found in the form, and those properties will be set for you. for example @ModelAttribute User user would give you a prepopulated user object from the registration form. This is what i want to do. But whats the point of the Command object?

axtavt Over a year ago

@mkoryak: I used the name Command as a placeholder for your own object, such as User in your example.

Luu Bieu Nghi · Accepted Answer · 2020-12-25 13:47:05Z

1

Here is the answer of your first question. http://chompingatbits.com/2009/08/25/spring-formtag-commandname-vs-modelattribute/

according to my experience there isn't easier way to fullfill validation, because it's easy enough. You can get it easier integrating libraries such as commons-validator into your project and use pre-defined validation rules in your forms.

http://numberformat.wordpress.com/tag/spring-mvc-validation/

and also with 3rd version of Spring you can use Bean validation using annotations.

edited Dec 25, 2020 at 13:47

Luu Bieu Nghi

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answered Dec 30, 2010 at 17:59

Erhan Bagdemir

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1 Comment

mkoryak Over a year ago

nice. so commandName is something old that i dont care about.

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