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Commons Digester example source code file (NodeCreateRule.java)

This example Commons Digester source code file (NodeCreateRule.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Commons Digester tags/keywords

attributes, dom, domexception, element, node, nodebuilder, nodebuilder, nodecreaterule, override, override, parser, parserconfigurationexception, sax, saxexception, saxexception, string, string, xml

The Commons Digester NodeCreateRule.java source code

/* $Id: NodeCreateRule.java 992060 2010-09-02 19:09:47Z simonetripodi $
 *
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */


package org.apache.commons.digester;


import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;

import org.w3c.dom.Attr;
import org.w3c.dom.DOMException;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.xml.sax.Attributes;
import org.xml.sax.ContentHandler;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;


/**
 * A rule implementation that creates a DOM
 * {@link org.w3c.dom.Node Node} containing the XML at the element that matched
 * the rule. Two concrete types of nodes can be created by this rule:
 * <ul>
 *   <li>the default is to create an {@link org.w3c.dom.Element Element} node.
 *   The created element will correspond to the element that matched the rule,
 *   containing all XML content underneath that element.</li>
 *   <li>alternatively, this rule can create nodes of type
 *   {@link org.w3c.dom.DocumentFragment DocumentFragment}, which will contain
 *   only the XML content under the element the rule was trigged on.</li>
 * </ul>
 * The created node will be normalized, meaning it will not contain text nodes 
 * that only contain white space characters.
 * 

 * 
 * <p>The created Node will be pushed on Digester's object stack
 * when done. To use it in the context of another DOM
 * {@link org.w3c.dom.Document Document}, it must be imported first, using the
 * Document method
 * {@link org.w3c.dom.Document#importNode(org.w3c.dom.Node, boolean) importNode()}.
 * </p>
 *
 * <p>Important Note: This is implemented by replacing the SAX
 * {@link org.xml.sax.ContentHandler ContentHandler} in the parser used by 
 * Digester, and resetting it when the matched element is closed. As a side 
 * effect, rules that would match XML nodes under the element that matches 
 * a <code>NodeCreateRule will never be triggered by Digester, which 
 * usually is the behavior one would expect.</p>
 * 
 * <p>Note that the current implementation does not set the namespace prefixes
 * in the exported nodes. The (usually more important) namespace URIs are set,
 * of course.</p>
 *
 * @since Digester 1.4
 */

public class NodeCreateRule extends Rule {


    // ---------------------------------------------------------- Inner Classes


    /**
     * The SAX content handler that does all the actual work of assembling the 
     * DOM node tree from the SAX events.
     */
    private class NodeBuilder
        extends DefaultHandler {


        // ------------------------------------------------------- Constructors


        /**
         * Constructor.
         * 
         * <p>Stores the content handler currently used by Digester so it can 
         * be reset when done, and initializes the DOM objects needed to 
         * build the node.</p>
         * 
         * @param doc the document to use to create nodes
         * @param root the root node
         * @throws ParserConfigurationException if the DocumentBuilderFactory 
         *   could not be instantiated
         * @throws SAXException if the XMLReader could not be instantiated by 
         *   Digester (should not happen)
         */
        public NodeBuilder(Document doc, Node root)
            throws ParserConfigurationException, SAXException {

            this.doc = doc;
            this.root = root;
            this.top = root;
            
            oldContentHandler = digester.getCustomContentHandler();

        }


        // ------------------------------------------------- Instance Variables


        /**
         * The content handler used by Digester before it was set to this 
         * content handler.
         */
        protected ContentHandler oldContentHandler = null;


        /**
         * Depth of the current node, relative to the element where the content
         * handler was put into action.
         */
        protected int depth = 0;


        /**
         * A DOM Document used to create the various Node instances.
         */
        protected Document doc = null;


        /**
         * The DOM node that will be pushed on Digester's stack.
         */
        protected Node root = null;


        /**
         * The current top DOM mode.
         */
        protected Node top = null;

        /**
         * The text content of the current top DOM node.
         */
        protected StringBuffer topText = new StringBuffer();


        // --------------------------------------------- Helper Methods

        /**
         * Appends a {@link org.w3c.dom.Text Text} node to the current node
         * if the content reported by the parser is not purely whitespace.
         */
        private void addTextIfPresent() throws SAXException {
            if (topText.length() > 0) {
                String str = topText.toString();
                topText.setLength(0);

                if (str.trim().length() > 0) {
                    // The contained text is not *pure* whitespace, so create
                    // a text node to hold it. Note that the "untrimmed" text
                    // is stored in the node.
                    try {
                        top.appendChild(doc.createTextNode(str));
                    } catch (DOMException e) {
                        throw new SAXException(e.getMessage());
                    }
                }
            }
        }

        // --------------------------------------------- ContentHandler Methods


        /**
         * Handle notification about text embedded within the current node.
         * <p>
         * An xml parser calls this when text is found. We need to ensure that this
         * text gets attached to the new Node we are creating - except in the case
         * where the only text in the node is whitespace.
         * <p>
         * There is a catch, however. According to the sax specification, a parser
         * does not need to pass all of the text content of a node in one go; it can
         * make multiple calls passing part of the data on each call. In particular,
         * when the body of an element includes xml entity-references, at least some
         * parsers make a separate call to this method to pass just the entity content.
         * <p>
         * In this method, we therefore just append the provided text to a
         * "current text" buffer. When the element end is found, or a child element
         * is found then we can check whether we have all-whitespace. See method
         * addTextIfPresent. 
         * 
         * @param ch the characters from the XML document
         * @param start the start position in the array
         * @param length the number of characters to read from the array
         * @throws SAXException if the DOM implementation throws an exception
         */
        @Override
        public void characters(char[] ch, int start, int length)
            throws SAXException {

            topText.append(ch, start, length);
        }


        /**
         * Checks whether control needs to be returned to Digester.
         * 
         * @param namespaceURI the namespace URI
         * @param localName the local name
         * @param qName the qualified (prefixed) name
         * @throws SAXException if the DOM implementation throws an exception
         */
        @Override
        public void endElement(String namespaceURI, String localName,
                               String qName)
            throws SAXException {
            
            addTextIfPresent();

            try {
                if (depth == 0) {
                    getDigester().setCustomContentHandler(oldContentHandler);
                    getDigester().push(root);
                    getDigester().endElement(namespaceURI, localName, qName);
                }
    
                top = top.getParentNode();
                depth--;
            } catch (DOMException e) {
                throw new SAXException(e.getMessage());
            }

        }


        /**
         * Adds a new
         * {@link org.w3c.dom.ProcessingInstruction ProcessingInstruction} to 
         * the current node.
         * 
         * @param target the processing instruction target
         * @param data the processing instruction data, or null if none was 
         *   supplied
         * @throws SAXException if the DOM implementation throws an exception
         */
        @Override
        public void processingInstruction(String target, String data)
            throws SAXException {
            
            try {
                top.appendChild(doc.createProcessingInstruction(target, data));
            } catch (DOMException e) {
                throw new SAXException(e.getMessage());
            }

        }


        /**
         * Adds a new child {@link org.w3c.dom.Element Element} to the current
         * node.
         * 
         * @param namespaceURI the namespace URI
         * @param localName the local name
         * @param qName the qualified (prefixed) name
         * @param atts the list of attributes
         * @throws SAXException if the DOM implementation throws an exception
         */
        @Override
        public void startElement(String namespaceURI, String localName,
                                 String qName, Attributes atts)
            throws SAXException {

            addTextIfPresent();

            try {
                Node previousTop = top;
                if ((localName == null) || (localName.length() == 0)) { 
                    top = doc.createElement(qName);
                } else {
                    top = doc.createElementNS(namespaceURI, localName);
                }
                for (int i = 0; i < atts.getLength(); i++) {
                    Attr attr = null;
                    if ((atts.getLocalName(i) == null) ||
                        (atts.getLocalName(i).length() == 0)) {
                        attr = doc.createAttribute(atts.getQName(i));
                        attr.setNodeValue(atts.getValue(i));
                        ((Element)top).setAttributeNode(attr);
                    } else {
                        attr = doc.createAttributeNS(atts.getURI(i),
                                                     atts.getLocalName(i));
                        attr.setNodeValue(atts.getValue(i));
                        ((Element)top).setAttributeNodeNS(attr);
                    }
                }
                previousTop.appendChild(top);
                depth++;
            } catch (DOMException e) {
                throw new SAXException(e.getMessage());
            }

        }

    }


    // ----------------------------------------------------------- Constructors


    /**
     * Default constructor. Creates an instance of this rule that will create a
     * DOM {@link org.w3c.dom.Element Element}.
     */
    public NodeCreateRule() throws ParserConfigurationException {

        this(Node.ELEMENT_NODE);

    }


    /**
     * Constructor. Creates an instance of this rule that will create a DOM
     * {@link org.w3c.dom.Element Element}, but lets you specify the JAXP 
     * <code>DocumentBuilder that should be used when constructing the
     * node tree.
     * 
     * @param documentBuilder the JAXP <code>DocumentBuilder to use
     */
    public NodeCreateRule(DocumentBuilder documentBuilder) {

        this(Node.ELEMENT_NODE, documentBuilder);

    }


    /**
     * Constructor. Creates an instance of this rule that will create either a 
     * DOM {@link org.w3c.dom.Element Element} or a DOM 
     * {@link org.w3c.dom.DocumentFragment DocumentFragment}, depending on the
     * value of the <code>nodeType parameter.
     * 
     * @param nodeType the type of node to create, which can be either
     *   {@link org.w3c.dom.Node#ELEMENT_NODE Node.ELEMENT_NODE} or 
     *   {@link org.w3c.dom.Node#DOCUMENT_FRAGMENT_NODE Node.DOCUMENT_FRAGMENT_NODE}
     * @throws IllegalArgumentException if the node type is not supported
     */
    public NodeCreateRule(int nodeType) throws ParserConfigurationException {

        this(nodeType,
             DocumentBuilderFactory.newInstance().newDocumentBuilder());

    }


    /**
     * Constructor. Creates an instance of this rule that will create either a 
     * DOM {@link org.w3c.dom.Element Element} or a DOM 
     * {@link org.w3c.dom.DocumentFragment DocumentFragment}, depending on the
     * value of the <code>nodeType parameter. This constructor lets you
     * specify the JAXP <code>DocumentBuilder that should be used when
     * constructing the node tree.
     * 
     * @param nodeType the type of node to create, which can be either
     *   {@link org.w3c.dom.Node#ELEMENT_NODE Node.ELEMENT_NODE} or 
     *   {@link org.w3c.dom.Node#DOCUMENT_FRAGMENT_NODE Node.DOCUMENT_FRAGMENT_NODE}
     * @param documentBuilder the JAXP <code>DocumentBuilder to use
     * @throws IllegalArgumentException if the node type is not supported
     */
    public NodeCreateRule(int nodeType, DocumentBuilder documentBuilder) {

        if (!((nodeType == Node.DOCUMENT_FRAGMENT_NODE) ||
              (nodeType == Node.ELEMENT_NODE))) {
            throw new IllegalArgumentException(
                "Can only create nodes of type DocumentFragment and Element");
        }
        this.nodeType = nodeType;
        this.documentBuilder = documentBuilder;

    }


    // ----------------------------------------------------- Instance Variables


    /**
     * The JAXP <code>DocumentBuilder to use.
     */
    private DocumentBuilder documentBuilder = null;


    /**
     * The type of the node that should be created. Must be one of the
     * constants defined in {@link org.w3c.dom.Node Node}, but currently only
     * {@link org.w3c.dom.Node#ELEMENT_NODE Node.ELEMENT_NODE} and 
     * {@link org.w3c.dom.Node#DOCUMENT_FRAGMENT_NODE Node.DOCUMENT_FRAGMENT_NODE}
     * are allowed values.
     */
    private int nodeType = Node.ELEMENT_NODE;


    // ----------------------------------------------------------- Rule Methods


    /**
     * When this method fires, the digester is told to forward all SAX
     * ContentHandler events to the builder object, resulting in a DOM being
     * built instead of normal digester rule-handling occurring. When the
     * end of the current xml element is encountered, the original content 
     * handler is restored (expected to be NULL, allowing normal Digester
     * operations to continue).
     * 
     * @param namespaceURI the namespace URI of the matching element, or an 
     *   empty string if the parser is not namespace aware or the element has
     *   no namespace
     * @param name the local name if the parser is namespace aware, or just 
     *   the element name otherwise
     * @param attributes The attribute list of this element
     * @throws Exception indicates a JAXP configuration problem
     */
    @Override
    public void begin(String namespaceURI, String name, Attributes attributes)
        throws Exception {

        Document doc = documentBuilder.newDocument();
        NodeBuilder builder = null;
        if (nodeType == Node.ELEMENT_NODE) {
            Element element = null;
            if (getDigester().getNamespaceAware()) {
                element =
                    doc.createElementNS(namespaceURI, name);
                for (int i = 0; i < attributes.getLength(); i++) {
                    element.setAttributeNS(attributes.getURI(i),
                                           attributes.getQName(i),
                                           attributes.getValue(i));
                }
            } else {
                element = doc.createElement(name);
                for (int i = 0; i < attributes.getLength(); i++) {
                    element.setAttribute(attributes.getQName(i),
                                         attributes.getValue(i));
                }
            }
            builder = new NodeBuilder(doc, element);
        } else {
            builder = new NodeBuilder(doc, doc.createDocumentFragment());
        }
        // the NodeBuilder constructor has already saved the original
        // value of the digester's custom content handler (expected to
        // be null, but we save it just in case). So now we just
        // need to tell the digester to forward events to the builder.
        getDigester().setCustomContentHandler(builder);
    }


    /**
     * Pop the Node off the top of the stack.
     */
    @Override
    public void end() throws Exception {

        digester.pop();

    }


}

Other Commons Digester examples (source code examples)

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