org.springframework.validation
Interface Validator

public interface Validator

A validator for application-specific objects.

This interface is totally divorced from any infrastructure or context; that is to say it is not coupled to validating only objects in the web tier, the data-access tier, or the whatever-tier. As such it is amenable to being used in any layer of an application, and supports the encapsulation of validation logic as first-class citizens in their own right.

Find below a simple but complete Validator implementation, that validates that the various String properties (fields) of a UserLogin instance are not empty (that is they are not null and do not consist wholly of whitespace), and that any password that is present is at least 'MINIMUM_PASSWORD_LENGTH' characters in length.

 public class UserLoginValidator implements Validator {
 
    private static final int MINIMUM_PASSWORD_LENGTH = 6;
 
    public boolean supports(Class clazz) {
       return UserLogin.class.isAssignableFrom(clazz);
    }
 
    public void validate(Object target, Errors errors) {
       ValidationUtils.rejectIfEmptyOrWhitespace(errors, "userName", "field.required");
       ValidationUtils.rejectIfEmptyOrWhitespace(errors, "password", "field.required");
       UserLogin login = (UserLogin) target;
       if (login.getPassword() != null
             && login.getPassword().trim().length() < MINIMUM_PASSWORD_LENGTH) {
          errors.rejectValue("password", "field.min.length",
                new Object[]{Integer.valueOf(MINIMUM_PASSWORD_LENGTH)},
                "The password must be at least [" + MINIMUM_PASSWORD_LENGTH + "] characters in length.");
       }
    }
 }

See also the Spring reference manual for a fuller discussion of the Validator interface and it's role in a enterprise application.

Author:

Rod Johnson

See Also:

Errors, ValidationUtils

Method Summary

boolean	supports(Class clazz) Can this Validator validate instances of the supplied clazz?
void	validate(Object target, Errors errors) Validate the supplied target object, which must be of a Class for which the supports(Class) method typically has (or would) return true.

Method Detail

supports

boolean supports(Class clazz)

Can this Validator validate instances of the supplied clazz?

This method is 'typically' implemented like so:

return Foo.class.isAssignableFrom(clazz);

(Where Foo is the class (or superclass) of the actual object instance that is to be validated).)

However, implementations can (of course) choose to implement this method in any manner they please.

Parameters:

clazz - the Class that this Validator is being asked if it can validate

Returns:

true if this Validator can indeed validate instances of the supplied clazz

validate

void validate(Object target,
              Errors errors)

Validate the supplied target object, which must be of a Class for which the supports(Class) method typically has (or would) return true.

The supplied errors instance can be used to report any resulting validation errors.

Parameters:

target - the object that is to be validated (can be null)

errors - contextual state about the validation process (never null)

See Also:

ValidationUtils