/**
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* $Id: mxCodec.java,v 1.1 2012/11/15 13:26:47 gaudenz Exp $
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* Copyright (c) 2012, JGraph Ltd
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*/
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package com.mxgraph.io;
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import java.util.Hashtable;
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import java.util.Map;
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import org.w3c.dom.Document;
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import org.w3c.dom.Element;
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import org.w3c.dom.Node;
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import com.mxgraph.model.mxCell;
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import com.mxgraph.model.mxCellPath;
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import com.mxgraph.model.mxICell;
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import com.mxgraph.util.mxDomUtils;
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import com.mxgraph.util.mxUtils;
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/**
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* XML codec for Java object graphs. In order to resolve forward references
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* when reading files the XML document that contains the data must be passed
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* to the constructor.
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*/
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public class mxCodec
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{
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/**
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* Holds the owner document of the codec.
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*/
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protected Document document;
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/**
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* Maps from IDs to objects.
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*/
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protected Map<String, Object> objects = new Hashtable<String, Object>();
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/**
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* Specifies if default values should be encoded. Default is false.
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*/
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protected boolean encodeDefaults = false;
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/**
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* Constructs an XML encoder/decoder with a new owner document.
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*/
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public mxCodec()
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{
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this(mxDomUtils.createDocument());
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}
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/**
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* Constructs an XML encoder/decoder for the specified owner document.
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*
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* @param document Optional XML document that contains the data. If no document
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* is specified then a new document is created using mxUtils.createDocument
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*/
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public mxCodec(Document document)
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{
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if (document == null)
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{
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document = mxDomUtils.createDocument();
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}
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this.document = document;
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}
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/**
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* Returns the owner document of the codec.
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*
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* @return Returns the owner document.
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*/
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public Document getDocument()
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{
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return document;
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}
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/**
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* Sets the owner document of the codec.
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*/
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public void setDocument(Document value)
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{
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document = value;
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}
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/**
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* Returns if default values of member variables should be encoded.
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*/
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public boolean isEncodeDefaults()
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{
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return encodeDefaults;
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}
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/**
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* Sets if default values of member variables should be encoded.
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*/
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public void setEncodeDefaults(boolean encodeDefaults)
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{
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this.encodeDefaults = encodeDefaults;
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}
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/**
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* Returns the object lookup table.
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*/
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public Map<String, Object> getObjects()
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{
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return objects;
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}
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/**
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* Assoiates the given object with the given ID.
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*
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* @param id ID for the object to be associated with.
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* @param object Object to be associated with the ID.
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* @return Returns the given object.
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*/
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public Object putObject(String id, Object object)
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{
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return objects.put(id, object);
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}
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/**
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* Returns the decoded object for the element with the specified ID in
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* {@link #document}. If the object is not known then {@link #lookup(String)}
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* is used to find an object. If no object is found, then the element with
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* the respective ID from the document is parsed using {@link #decode(Node)}.
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*
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* @param id ID of the object to be returned.
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* @return Returns the object for the given ID.
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*/
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public Object getObject(String id)
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{
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Object obj = null;
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if (id != null)
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{
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obj = objects.get(id);
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if (obj == null)
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{
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obj = lookup(id);
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if (obj == null)
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{
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Node node = getElementById(id);
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if (node != null)
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{
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obj = decode(node);
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}
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}
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}
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}
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return obj;
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}
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/**
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* Hook for subclassers to implement a custom lookup mechanism for cell IDs.
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* This implementation always returns null.
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*
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* @param id ID of the object to be returned.
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* @return Returns the object for the given ID.
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*/
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public Object lookup(String id)
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{
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return null;
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}
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/**
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* Returns the element with the given ID from the document.
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*
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* @param id ID of the element to be returned.
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* @return Returns the element for the given ID.
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*/
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public Node getElementById(String id)
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{
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return getElementById(id, null);
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}
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/**
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* Returns the element with the given ID from document. The optional attr
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* argument specifies the name of the ID attribute. Default is "id". The
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* XPath expression used to find the element is //*[@attr='arg'] where attr
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* is the name of the ID attribute and arg is the given id.
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*
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* Parameters:
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*
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* id - String that contains the ID.
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* attr - Optional string for the attributename. Default is id.
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*/
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public Node getElementById(String id, String attr)
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{
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if (attr == null)
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{
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attr = "id";
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}
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String expr = "//*[@" + attr + "='" + id + "']";
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return mxUtils.selectSingleNode(document, expr);
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}
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/**
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* Returns the ID of the specified object. This implementation calls
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* reference first and if that returns null handles the object as an
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* mxCell by returning their IDs using mxCell.getId. If no ID exists for
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* the given cell, then an on-the-fly ID is generated using
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* mxCellPath.create.
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*
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* @param obj Object to return the ID for.
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* @return Returns the ID for the given object.
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*/
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public String getId(Object obj)
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{
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String id = null;
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if (obj != null)
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{
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id = reference(obj);
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if (id == null && obj instanceof mxICell)
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{
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id = ((mxICell) obj).getId();
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if (id == null)
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{
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// Uses an on-the-fly Id
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id = mxCellPath.create((mxICell) obj);
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if (id.length() == 0)
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{
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id = "root";
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}
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}
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}
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}
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return id;
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}
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/**
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* Hook for subclassers to implement a custom method for retrieving IDs from
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* objects. This implementation always returns null.
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*
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* @param obj Object whose ID should be returned.
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* @return Returns the ID for the given object.
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*/
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public String reference(Object obj)
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{
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return null;
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}
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/**
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* Encodes the specified object and returns the resulting XML node.
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*
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* @param obj Object to be encoded.
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* @return Returns an XML node that represents the given object.
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*/
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public Node encode(Object obj)
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{
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Node node = null;
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if (obj != null)
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{
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String name = mxCodecRegistry.getName(obj);
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mxObjectCodec enc = mxCodecRegistry.getCodec(name);
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if (enc != null)
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{
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node = enc.encode(this, obj);
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}
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else
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{
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if (obj instanceof Node)
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{
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node = ((Node) obj).cloneNode(true);
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}
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else
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{
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System.err.println("No codec for " + name);
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}
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}
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}
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return node;
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}
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/**
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* Decodes the given XML node using {@link #decode(Node, Object)}.
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*
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* @param node XML node to be decoded.
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* @return Returns an object that represents the given node.
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*/
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public Object decode(Node node)
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{
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return decode(node, null);
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}
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/**
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* Decodes the given XML node. The optional "into" argument specifies an
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* existing object to be used. If no object is given, then a new
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* instance is created using the constructor from the codec.
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*
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* The function returns the passed in object or the new instance if no
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* object was given.
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*
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* @param node XML node to be decoded.
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* @param into Optional object to be decodec into.
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* @return Returns an object that represents the given node.
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*/
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public Object decode(Node node, Object into)
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{
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Object obj = null;
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if (node != null && node.getNodeType() == Node.ELEMENT_NODE)
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{
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mxObjectCodec codec = mxCodecRegistry.getCodec(node.getNodeName());
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try
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{
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if (codec != null)
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{
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obj = codec.decode(this, node, into);
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}
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else
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{
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obj = node.cloneNode(true);
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((Element) obj).removeAttribute("as");
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}
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}
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catch (Exception e)
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{
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System.err.println("Cannot decode " + node.getNodeName() + ": "
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+ e.getMessage());
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e.printStackTrace();
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}
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}
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return obj;
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}
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/**
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* Encoding of cell hierarchies is built-into the core, but is a
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* higher-level function that needs to be explicitely used by the
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* respective object encoders (eg. mxModelCodec, mxChildChangeCodec
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* and mxRootChangeCodec). This implementation writes the given cell
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* and its children as a (flat) sequence into the given node. The
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* children are not encoded if the optional includeChildren is false.
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* The function is in charge of adding the result into the given node
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* and has no return value.
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*
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* @param cell mxCell to be encoded.
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* @param node Parent XML node to add the encoded cell into.
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* @param includeChildren Boolean indicating if the method
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* should include all descendents.
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*/
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public void encodeCell(mxICell cell, Node node, boolean includeChildren)
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{
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node.appendChild(encode(cell));
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if (includeChildren)
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{
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int childCount = cell.getChildCount();
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for (int i = 0; i < childCount; i++)
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{
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encodeCell(cell.getChildAt(i), node, includeChildren);
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}
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}
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}
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/**
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* Decodes cells that have been encoded using inversion, ie. where the
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* user object is the enclosing node in the XML, and restores the group
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* and graph structure in the cells. Returns a new <mxCell> instance
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* that represents the given node.
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*
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* @param node XML node that contains the cell data.
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* @param restoreStructures Boolean indicating whether the graph
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* structure should be restored by calling insert and insertEdge on the
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* parent and terminals, respectively.
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* @return Graph cell that represents the given node.
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*/
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public mxICell decodeCell(Node node, boolean restoreStructures)
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{
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mxICell cell = null;
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if (node != null && node.getNodeType() == Node.ELEMENT_NODE)
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{
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// Tries to find a codec for the given node name. If that does
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// not return a codec then the node is the user object (an XML node
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// that contains the mxCell, aka inversion).
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mxObjectCodec decoder = mxCodecRegistry
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.getCodec(node.getNodeName());
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// Tries to find the codec for the cell inside the user object.
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// This assumes all node names inside the user object are either
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// not registered or they correspond to a class for cells.
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if (!(decoder instanceof mxCellCodec))
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{
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Node child = node.getFirstChild();
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while (child != null && !(decoder instanceof mxCellCodec))
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{
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decoder = mxCodecRegistry.getCodec(child.getNodeName());
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child = child.getNextSibling();
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}
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String name = mxCell.class.getSimpleName();
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decoder = mxCodecRegistry.getCodec(name);
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}
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if (!(decoder instanceof mxCellCodec))
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{
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String name = mxCell.class.getSimpleName();
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decoder = mxCodecRegistry.getCodec(name);
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}
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cell = (mxICell) decoder.decode(this, node);
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if (restoreStructures)
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{
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insertIntoGraph(cell);
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}
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}
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return cell;
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}
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/**
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* Inserts the given cell into its parent and terminal cells.
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*/
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public void insertIntoGraph(mxICell cell)
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{
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mxICell parent = cell.getParent();
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mxICell source = cell.getTerminal(true);
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mxICell target = cell.getTerminal(false);
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// Fixes possible inconsistencies during insert into graph
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cell.setTerminal(null, false);
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cell.setTerminal(null, true);
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cell.setParent(null);
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if (parent != null)
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{
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parent.insert(cell);
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}
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if (source != null)
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{
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source.insertEdge(cell, true);
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}
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if (target != null)
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{
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target.insertEdge(cell, false);
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}
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}
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/**
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* Sets the attribute on the specified node to value. This is a
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* helper method that makes sure the attribute and value arguments
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* are not null.
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*
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* @param node XML node to set the attribute for.
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* @param attribute Name of the attribute whose value should be set.
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* @param value New value of the attribute.
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*/
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public static void setAttribute(Node node, String attribute, Object value)
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{
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if (node.getNodeType() == Node.ELEMENT_NODE && attribute != null
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&& value != null)
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{
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((Element) node).setAttribute(attribute, String.valueOf(value));
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}
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}
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}
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