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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.
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 |
|---|
boolean supports(Class clazz)
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.)
clazz - the Class that this Validator is
being asked if it can validate
true if this Validator can indeed
validate instances of the
supplied clazz
void validate(Object target,
Errors errors)
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.
target - the object that is to be validated (can be null)errors - contextual state about the validation process (never null)ValidationUtils
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