XmlNodeHelper.java from SmartFrog at Krugle

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/** (C) Copyright 1998-2005 Hewlett-Packard Development Company, LP

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The Software is provided "AS IS," without a warranty of any kind. ALL
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EXCLUDED. SmartFrog is not a Hewlett-Packard Product. The Software has
not undergone complete testing and may contain errors and defects. It
may not function properly and is subject to change or withdrawal at
any time. The user must assume the entire risk of using the
Software. No support or maintenance is provided with the Software by
Hewlett-Packard. Do not install the Software if you are not accustomed
to using experimental software.

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TO THE EXTENT NOT PROHIBITED BY LAW, IN NO EVENT WILL HEWLETT-PACKARD
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*/
package org.smartfrog.services.xml.impl;

import nu.xom.Node;
import nu.xom.XMLException;
import org.smartfrog.services.xml.interfaces.LocalNode;
import org.smartfrog.services.xml.interfaces.XmlNode;
import org.smartfrog.sfcore.common.SmartFrogException;
import org.smartfrog.sfcore.common.SmartFrogLivenessException;
import org.smartfrog.sfcore.prim.Prim;

import java.rmi.RemoteException;

/**
 * Class to contain helper logic for a node
 */
public final class XmlNodeHelper implements XmlNode {
    /**
     * text of the message when wrapping a {@link nu.xom.XMLException} with a
     * {@link SmartFrogException}
     */
    public static final String ERROR_XML_FAULT = "XML exception when creating node or generating XML";

    public XmlNodeHelper(LocalNode owner) {
        this.owner = owner;
        ownerAsPrim = (Prim) owner;
    }

    /**
     * owning node
     */
    private LocalNode owner;

    /**
     * our owner as a prim
     */
    private Prim ownerAsPrim;

    /**
     * this is our underlying node.
     */
    private Node node;

    /**
     * XML data.
     */
    private String xml;

    /**
     * set the node
     *
     * @param node
     */
    public void setNode(Node node) {
        this.node = node;
    }

    /**
     * get the current node value
     *
     * @return
     */
    public Node getNode() {
        return node;
    }

    /**
     * set the XML
     *
     * @param xml
     */
    public void setXml(String xml) {
        this.xml = xml;
    }

    /**
     * get the last XML evaluated
     *
     * @return the XML; may be null
     */
    public String getXml() {
        return xml;
    }

    /**
     * generate XML from the doc. This always triggers a recalculate of
     * everything, then the attribute is saved. We do it this way because we
     * don't know what has changed underneath.
     *
     * @return XML of the tree
     * @throws RemoteException In case of network/rmi error
     * @throws SmartFrogException For smartfrog problems, and for caught
     *                            XMLExceptions
     */
    public String toXML() throws RemoteException, SmartFrogException {
        try {
            if (node == null) {
                //demand create the node
                node = owner.createNode();
            }
            xml = node.toXML();
        } catch (XMLException e) {
            throw new SmartFrogException(XmlNodeHelper.ERROR_XML_FAULT,
                    e,
                    ownerAsPrim);
        }
        ownerAsPrim.sfReplaceAttribute(ATTR_XML, xml);
        validate();
        return xml;
    }

    /**
     * Validate the XML, post-generation. Default implementation checks the
     * <code>valid</code> attribute and fails if it is false.
     *
     * @throws RemoteException In case of network/rmi error
     * @throws SmartFrogException For smartfrog problems, and for caught
     *                            XMLExceptions
     */
    public void validate() throws SmartFrogException,
            RemoteException {
        boolean valid = ownerAsPrim.sfResolve(ATTR_VALID, true, true);
        if (!valid) {
            throw new SmartFrogLivenessException("XML fails validity test :"
                    + xml,
                    ownerAsPrim);
        }
    }

    /**
     * equality test compares node values
     * @param o
     * @return true if they are equal
     */
    public boolean equals(Object o) {
        if (this == o) {
            return true;
        }
        if (!(o instanceof XmlNodeHelper)) {
            return false;
        }

        final XmlNodeHelper xmlNodeHelper = (XmlNodeHelper) o;

        if (node != null ?
                !node.equals(xmlNodeHelper.node) :
                xmlNodeHelper.node != null) {
            return false;
        }

        return true;
    }

    /**
     * hash code is derived from the node
     * @return hascode of the node
     */
    public int hashCode() {
        return (node != null ? node.hashCode() : 0);
    }


    /**
     * mape from an XMLException (extending RuntimeException) into a
     * SmartFrogException, which can then be thrown.
     * @param xmle XML exception
     * @return an instantiated and configured SmartFrogException.
     */
    public static SmartFrogException handleXmlException(XMLException xmle) {
        SmartFrogException sfe=new SmartFrogException(xmle);
        return sfe;
    }
}
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