001// Copyright 2004, 2005 The Apache Software Foundation
002//
003// Licensed under the Apache License, Version 2.0 (the "License");
004// you may not use this file except in compliance with the License.
005// You may obtain a copy of the License at
006//
007//     http://www.apache.org/licenses/LICENSE-2.0
008//
009// Unless required by applicable law or agreed to in writing, software
010// distributed under the License is distributed on an "AS IS" BASIS,
011// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
012// See the License for the specific language governing permissions and
013// limitations under the License.
014
015package org.apache.tapestry.valid;
016
017import org.apache.tapestry.IMarkupWriter;
018import org.apache.tapestry.IRequestCycle;
019import org.apache.tapestry.form.IFormComponent;
020
021/**
022 * An object that works with an {@link IFormComponent} to format output (convert object values to
023 * strings values) and to process input (convert strings to object values and validate them).
024 * <p>
025 * Note that this interface represents validation as supported in Tapestry 2.x to 3.0. It has been
026 * outdated (and will eventually be deprecated) by new support in Tapestry 4.0, centered around the
027 * {@link org.apache.tapestry.form.translator.Translator} and
028 * {@link org.apache.tapestry.form.validator.Validator} interfaces.
029 * 
030 * @author Howard Lewis Ship
031 * @since 1.0.8
032 */
033
034public interface IValidator
035{
036    /**
037     * All validators must implement a required property. If true, the client must supply a non-null
038     * value.
039     */
040
041    public boolean isRequired();
042
043    /**
044     * Invoked during rendering to convert an object value (which may be null) to a String. It is
045     * acceptible to return null. The string will be the VALUE attribute of the HTML text field.
046     */
047
048    public String toString(IFormComponent field, Object value);
049
050    /**
051     * Converts input, submitted by the client, into an object value. May return null if the input
052     * is null (and the required flag is false).
053     * <p>
054     * The input string will already have been trimmed. It may be null.
055     * 
056     * @throws ValidatorException
057     *             if the string cannot be converted into an object, or the object is not valid (due
058     *             to other constraints).
059     */
060
061    public Object toObject(IFormComponent field, String input) throws ValidatorException;
062
063    /**
064     * Invoked by the field after it finishes rendering its tag (but before the tag is closed) to
065     * allow the validator to provide a contribution to the rendering process. Validators typically
066     * generated client-side JavaScript to peform validation.
067     * 
068     * @since 2.2
069     */
070
071    public void renderValidatorContribution(IFormComponent field, IMarkupWriter writer,
072            IRequestCycle cycle);
073
074}