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, which validates that the various String properties 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.)

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