/*
* Copyright 2002-2012 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.validation;
/**
* A validator for application-specific objects.
*
* <p>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.
*
* <p>Find below a simple but complete {@code Validator}
* implementation, which validates that the various {@link String}
* properties of a {@code UserLogin} instance are not empty
* (that is they are not {@code null} and do not consist
* wholly of whitespace), and that any password that is present is
* at least {@code 'MINIMUM_PASSWORD_LENGTH'} characters in length.
*
* <pre class="code"> 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.");
* }
* }
* }</pre>
*
* <p>See also the Spring reference manual for a fuller discussion of
* the {@code Validator} interface and its role in an enterprise
* application.
*
* @author Rod Johnson
* @see Errors
* @see ValidationUtils
*/
public interface Validator {
/**
* Can this {@link Validator} {@link #validate(Object, Errors) validate}
* instances of the supplied {@code clazz}?
* <p>This method is <i>typically</i> implemented like so:
* <pre class="code">return Foo.class.isAssignableFrom(clazz);</pre>
* (Where {@code Foo} is the class (or superclass) of the actual
* object instance that is to be {@link #validate(Object, Errors) validated}.)
* @param clazz the {@link Class} that this {@link Validator} is
* being asked if it can {@link #validate(Object, Errors) validate}
* @return {@code true} if this {@link Validator} can indeed
* {@link #validate(Object, Errors) validate} instances of the
* supplied {@code clazz}
*/
boolean supports(Class<?> clazz);
/**
* Validate the supplied {@code target} object, which must be
* of a {@link Class} for which the {@link #supports(Class)} method
* typically has (or would) return {@code true}.
* <p>The supplied {@link Errors errors} instance can be used to report
* any resulting validation errors.
* @param target the object that is to be validated (can be {@code null})
* @param errors contextual state about the validation process (never {@code null})
* @see ValidationUtils
*/
void validate(Object target, Errors errors);
}