Package org.springframework.validation

Interface Validator

All Known Subinterfaces:

SmartValidator

All Known Implementing Classes:

CustomValidatorBean, LocalValidatorFactoryBean, OptionalValidatorFactoryBean, SpringValidatorAdapter

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 a first-class citizen in its 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 its role in an enterprise application.

Author:

Rod Johnson

See Also:

• SmartValidator
• Errors
• ValidationUtils
• DataBinder.setValidator(org.springframework.validation.Validator)

Method Summary

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

Method Details

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

The supplied errors instance can be used to report any resulting validation errors, typically as part of a larger binding process which this validator is meant to participate in. Binding errors have typically been pre-registered with the errors instance before this invocation already.

Parameters:

target - the object that is to be validated

errors - contextual state about the validation process

See Also:

• ValidationUtils