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package org.springframework.validation;

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:
/** * 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 SmartValidator * @see Errors * @see ValidationUtils */
public interface Validator {
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.)
Params:
Returns:true if this Validator can indeed validate instances of the supplied clazz
/** * 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 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.

Params:
  • target – the object that is to be validated
  • errors – contextual state about the validation process
See Also:
/** * 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 * @param errors contextual state about the validation process * @see ValidationUtils */
void validate(Object target, Errors errors); }