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package javax.faces.validator;

import javax.faces.component.UIComponent;
import javax.faces.context.FacesContext;
import java.util.EventListener;


/**
 * <p>A <strong class="changed_modified_2_0">Validator</strong>
 * implementation is a class that can perform validation (correctness
 * checks) on a {@link javax.faces.component.EditableValueHolder}.  Zero
 * or more <code>Validator</code>s can be associated with each {@link
 * javax.faces.component.EditableValueHolder} in the view, and are
 * called during the <em>Process Validations</em> phase of the request
 * processing lifecycle.</p>

 * <p/>
 * <p>Individual {@link Validator}s should examine the value and
 * component that they are passed, and throw a {@link ValidatorException}
 * containing a {@link javax.faces.application.FacesMessage}, documenting
 * any failures to conform to the required rules.
 * <p/>
 * <p>For maximum generality, {@link Validator} instances may be
 * configurable based on properties of the {@link Validator} implementation
 * class.  For example, a range check {@link Validator} might support
 * configuration of the minimum and maximum values to be used.</p>
 * <p/>
 * <p>{@link Validator} implementations must have a zero-arguments
 * public constructor.  In addition, if the {@link Validator} class
 * wishes to have configuration property values saved and restored with
 * the view, the implementation must also implement {@link
 * javax.faces.component.StateHolder}.</p>

 * <p class="changed_added_2_0">If the class implementing
 * <code>Validator</code> has a {@link
 * javax.faces.application.ResourceDependency} annotation, the action
 * described in <code>ResourceDependency</code> must be taken when
 * {@link javax.faces.component.EditableValueHolder#addValidator} is
 * called.  If the class implementing <code>Validator</code> has a {@link
 * javax.faces.application.ResourceDependencies} annotation, the
 * action described in <code>ResourceDependencies</code> must be taken
 * when {@link javax.faces.component.EditableValueHolder#addValidator} 
 * is called.</p>

 */

public interface Validator extends EventListener {

    /**
     * <p>The message identifier of the {@link javax.faces.application.FacesMessage} to be created if
     * the maximum or minimum value check fails, and both the maximum
     * and minimum values for this validator have been set.  The message
     * format string for this message may optionally include a
     * <code>{0}</code> placeholder, which will be replaced by the
     * configured minimum value, and a <code>{1}</code> placeholder,
     * which will be replaced by the configured maximum value.</p>
     *
     * @deprecated Use {@link DoubleRangeValidator#NOT_IN_RANGE_MESSAGE_ID} or
     *             {@link LongRangeValidator#NOT_IN_RANGE_MESSAGE_ID} instead.
     */
    public static final String NOT_IN_RANGE_MESSAGE_ID =
         "javax.faces.validator.NOT_IN_RANGE";

    /**
     * <p><span class="changed_modified_2_0">Perform</span> the
     * correctness checks implemented by this {@link Validator} against
     * the specified {@link UIComponent}.  If any violations are found,
     * a {@link ValidatorException} will be thrown containing the {@link
     * javax.faces.application.FacesMessage} describing the failure.
     *
     * <div class="changed_added_2_0">
     *
     * <p>For a validator to be fully compliant with Version 2 and later
     * of the specification, it must not fail validation on
     * <code>null</code> or empty values unless it is specifically
     * intended to address <code>null</code> or empty values.  An
     * application-wide <code>&lt;context-param&gt;</code> is provided
     * to allow validators designed for JSF 1.2 to work with JSF 2 and
     * later. The <code>javax.faces.VALIDATE_EMPTY_FIELDS</code>
     * <code>&lt;context-param&gt;</code> must be set to
     * <code>false</code> to enable this backwards compatibility
     * behavior.</p>
     *
     * </div>
     *
     * @param context   FacesContext for the request we are processing
     * @param component UIComponent we are checking for correctness
     * @param value     the value to validate
     * @throws ValidatorException   if validation fails
     * @throws NullPointerException if <code>context</code>
     *                              or <code>component</code> is <code>null</code>
     */
    public void validate(FacesContext context,
                         UIComponent component,
                         Object value) throws ValidatorException;


}
