001/*
002 * Transform.java May 2007
003 *
004 * Copyright (C) 2007, Niall Gallagher <niallg@users.sf.net>
005 *
006 * Licensed under the Apache License, Version 2.0 (the "License");
007 * you may not use this file except in compliance with the License.
008 * You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or 
015 * implied. See the License for the specific language governing 
016 * permissions and limitations under the License.
017 */
018
019package org.simpleframework.xml.transform;
020
021/**
022 * A <code>Transform</code> represents a an object used to transform
023 * an object to and from a string value. This is typically used when
024 * either an <code>Attribute</code> or <code>Element</code> annotation
025 * is used to mark the field of a type that does not contain any of
026 * the XML annotations, and so does not represent an XML structure.
027 * For example take the following annotation.
028 * <pre>
029 * 
030 *    &#64;Text
031 *    private Date date;
032 *    
033 * </pre> 
034 * The above annotation marks an object from the Java class libraries
035 * which does not contain any XML annotations. During serialization
036 * and deserialization of such types a transform is used to process
037 * the object such that it can be written and read to and from XML.
038 * 
039 * @author Niall Gallagher
040 */
041public interface Transform<T> {
042   
043   /**
044    * This method is used to convert the string value given to an
045    * appropriate representation. This is used when an object is
046    * being deserialized from the XML document and the value for
047    * the string representation is required.
048    * 
049    * @param value this is the string representation of the value
050    * 
051    * @return this returns an appropriate instanced to be used
052    */
053    T read(String value) throws Exception;
054    
055    /**
056     * This method is used to convert the provided value into an XML
057     * usable format. This is used in the serialization process when
058     * there is a need to convert a field value in to a string so 
059     * that that value can be written as a valid XML entity.
060     * 
061     * @param value this is the value to be converted to a string
062     * 
063     * @return this is the string representation of the given value
064     */
065    String write(T value) throws Exception;
066}