001/*
002 * Visitor.java January 2010
003 *
004 * Copyright (C) 2010, 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.strategy;
020
021import org.simpleframework.xml.stream.InputNode;
022import org.simpleframework.xml.stream.NodeMap;
023import org.simpleframework.xml.stream.OutputNode;
024
025/**
026 * The <code>Visitor</code> interface represents an object that is 
027 * used to visit each XML element during serialization. For the
028 * deserialization process each XML element is visited before 
029 * control is returned to the serializer. This allows a visitor
030 * implementation to perform some operation based on the node 
031 * that is being deserialized. Typically a visitor is used to
032 * edit the node, for example it may remove or insert attributes.
033 * <p>
034 * In effect this can act much like a transformer that sits
035 * between a <code>Strategy</code> implementation and the core
036 * serializer. It enables interception and manipulation of the
037 * node so that the resulting XML document can be customized in 
038 * a way that can not be performed by the underlying strategy.
039 * 
040 * @author Niall Gallagher
041 * 
042 * @see org.simpleframework.xml.strategy.VisitorStrategy
043 */
044public interface Visitor {
045   
046   /**
047    * This is used to intercept an XML element before it is read
048    * by the underlying <code>Strategy</code> implementation. When
049    * a node is intercepted it can be manipulated in such a way
050    * that its semantics change. For example, this could be used 
051    * to change the way a "class" attribute is represented, which
052    * would allow the XML to appear in a language neutral format.
053    *
054    * @param type this is the type that represents the element
055    * @param node this is the XML element to be intercepted
056    */
057   void read(Type type, NodeMap<InputNode> node) throws Exception;
058   
059   /**
060    * This is used to intercept an XML element after it is written
061    * by the underlying <code>Strategy</code> implementation. When
062    * a node is intercepted it can be manipulated in such a way
063    * that its semantics change. For example, this could be used 
064    * to change the way a "class" attribute is represented, which
065    * would allow the XML to appear in a language neutral format.
066    *
067    * @param type this is the type that represents the element
068    * @param node this is the XML element to be intercepted
069    */
070   void write(Type type, NodeMap<OutputNode> node) throws Exception;
071}