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