File: XMLBuilder.java

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/*
 * Copyright 2008 James Murty (www.jamesmurty.com)
 *
 * Licensed 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.
 * 
 * 
 * This code is available from the Google Code repository at:
 * http://code.google.com/p/java-xmlbuilder
 */
package com.jamesmurty.utils;

import java.io.IOException;
import java.io.StringWriter;
import java.io.Writer;
import java.util.Iterator;
import java.util.Properties;
import java.util.Map.Entry;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.FactoryConfigurationError;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpression;
import javax.xml.xpath.XPathExpressionException;
import javax.xml.xpath.XPathFactory;

import net.iharder.base64.Base64;

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;

/**
 * XML Builder is a utility that creates simple XML documents using relatively 
 * sparse Java code. It is intended to allow for quick and painless creation of 
 * XML documents where you might otherwise be tempted to use concatenated 
 * strings, rather than face the tedium and verbosity of coding with 
 * JAXP (http://jaxp.dev.java.net/).
 * <p>
 * Internally, XML Builder uses JAXP to build a standard W3C 
 * {@link org.w3c.dom.Document} model (DOM) that you can easily export as a 
 * string, or access and manipulate further if you have special requirements.
 * </p> 
 * <p>
 * The XMLBuilder class serves as a wrapper of {@link org.w3c.dom.Element} nodes,
 * and provides a number of utility methods that make it simple to
 * manipulate the underlying element and the document to which it belongs. 
 * In essence, this class performs dual roles: it represents a specific XML 
 * node, and also allows manipulation of the entire underlying XML document.
 * The platform's default {@link DocumentBuilderFactory} and 
 * {@link DocumentBuilder} classes are used to build the document.
 * </p>
 *  
 * @author James Murty
 */
public class XMLBuilder {
    /**
     * A DOM Document that stores the underlying XML document operated on by 
     * XMLBuilder instances. This document object belongs to the root node
     * of a document, and is shared by this node with all other XMLBuilder 
     * instances via the {@link #getDocument()} method. 
     * This instance variable must only be created once, by the root node for 
     * any given document. 
     */
    private Document xmlDocument = null;

    /**
     * The underlying element represented by this builder node. 
     */
    private Element xmlElement = null;

    /**
     * Construct a new builder object that wraps the given XML document.
     * This constructor is for internal use only.
     * 
     * @param xmlDocument
     * an XML document that the builder will manage and manipulate.
     */
    protected XMLBuilder(Document xmlDocument) {
        this.xmlDocument = xmlDocument;
        this.xmlElement = xmlDocument.getDocumentElement();
    }

    /**
     * Construct a new builder object that wraps the given XML document
     * and element element.
     * This constructor is for internal use only.
     * 
     * @param myElement
     * the XML element that this builder node will wrap. This element may 
     * be part of the XML document, or it may be a new element that is to be
     * added to the document.
     * @param parentElement
     * If not null, the given myElement will be appended as child node of the 
     * parentElement node.
     */
    protected XMLBuilder(Element myElement, Element parentElement) {
        this.xmlElement = myElement;
        this.xmlDocument = myElement.getOwnerDocument();
        if (parentElement != null) {
        	parentElement.appendChild(myElement);
        }
    }
    
    /**
     * Construct a builder for new XML document. The document will be created
     * with the given root element, and the builder returned by this method
     * will serve as the starting-point for any further document additions.
     * 
     * @param name
     * the name of the document's root element.
     * @return
     * a builder node that can be used to add more nodes to the XML document.
     * 
     * @throws FactoryConfigurationError 
     * @throws ParserConfigurationException 
     */
    public static XMLBuilder create(String name) 
        throws ParserConfigurationException, FactoryConfigurationError 
    {
        // Init DOM builder and Document.
        DocumentBuilder builder = 
            DocumentBuilderFactory.newInstance().newDocumentBuilder();
        Document document = builder.newDocument();
        Element rootElement = document.createElement(name);
        document.appendChild(rootElement);
        return new XMLBuilder(document);
    }

    /**
     * Construct a builder from an existing XML document. The provided XML
     * document will be parsed and an XMLBuilder object referencing the
     * document's root element will be returned.
     * 
     * @param inputSource
     * an XML document input source that will be parsed into a DOM.
     * @return
     * a builder node that can be used to add more nodes to the XML document.
     * @throws ParserConfigurationException 
     * 
     * @throws FactoryConfigurationError 
     * @throws ParserConfigurationException 
     * @throws IOException 
     * @throws SAXException 
     */
    public static XMLBuilder parse(InputSource inputSource) 
    	throws ParserConfigurationException, SAXException, IOException 
    {
        DocumentBuilder builder = 
            DocumentBuilderFactory.newInstance().newDocumentBuilder();
        Document document = builder.parse(inputSource);
        return new XMLBuilder(document);
    }
    
    /**
     * @return
     * true if the XML Document and Element objects wrapped by this
     * builder are equal to the other's wrapped objects.
     */
    public boolean equals(Object obj) {
    	if (obj != null && obj instanceof XMLBuilder) {
    		XMLBuilder other = (XMLBuilder) obj;
    		return 
    			this.xmlDocument.equals(other.getDocument())
    			&& this.xmlElement.equals(other.getElement());
    	}
    	return false;
    }

    /**
     * @return
     * the XML element that this builder node will manipulate.
     */
    public Element getElement() {
        return this.xmlElement;
    }

    /**
     * @return
     * the builder node representing the root element of the XML document.
     * In other words, the same builder node returned by the initial 
     * {@link #create(String)} or {@link #parse(InputSource)} method.
     */
    public XMLBuilder root() {
        return new XMLBuilder(getDocument());
    }
    
    /**
     * @return
     * the XML document constructed by all builder nodes.
     */
    public Document getDocument() {
    	return this.xmlDocument;
    }
    
    /**
     * Find the first element in the builder's DOM matching the given
     * XPath expression. 
     * 
     * @param xpath
     * An XPath expression that *must* resolve to an existing Element within
     * the document object model. 
     * 
     * @return
     * a builder node representing the first Element that matches the 
     * XPath expression.
     * 
     * @throws XPathExpressionException
     * If the XPath is invalid, or if does not resolve to at least one
     * {@link Node.ELEMENT_NODE}.
     */
    public XMLBuilder xpathFind(String xpath) throws XPathExpressionException {
    	XPathFactory xpathFactory = XPathFactory.newInstance();
    	XPathExpression xpathExp = xpathFactory.newXPath().compile(xpath);
    	Node foundNode = (Node) xpathExp.evaluate(this.xmlElement, XPathConstants.NODE);
    	if (foundNode == null || foundNode.getNodeType() != Node.ELEMENT_NODE) {
    		throw new XPathExpressionException("XPath expression \"" 
				+ xpath + "\" does not resolve to an Element in context "
				+ this.xmlElement + ": " + foundNode);
    	}
    	return new XMLBuilder((Element) foundNode, null);
    }
    
    /**
     * Add a named XML element to the document as a child of this builder node,
     * and return the builder node representing the new child. 
     * 
     * @param name
     * the name of the XML element.
     * 
     * @return
     * a builder node representing the new child.
     * 
     * @throws IllegalStateException
     * if you attempt to add a child element to an XML node that already 
     * contains a text node value.
     */
    public XMLBuilder element(String name) {
        // Ensure we don't create sub-elements in Elements that already have text node values.
        Node textNode = null;
        NodeList childNodes = xmlElement.getChildNodes();
        for (int i = 0; i < childNodes.getLength(); i++) {
            if (Element.TEXT_NODE == childNodes.item(i).getNodeType()) {
                textNode = childNodes.item(i);
                break;
            }
        }
        if (textNode != null) {
            throw new IllegalStateException("Cannot add sub-element <" +
                name + "> to element <" + xmlElement.getNodeName() 
                + "> that already contains the Text node: " + textNode);
        }
        
        return new XMLBuilder(getDocument().createElement(name), this.xmlElement);        
    }
    
    /**
     * Synonym for {@link #element(String)}. 
     * 
     * @param name
     * the name of the XML element.
     * 
     * @return
     * a builder node representing the new child.
     * 
     * @throws IllegalStateException
     * if you attempt to add a child element to an XML node that already 
     * contains a text node value.
     */
    public XMLBuilder elem(String name) {
        return element(name);
    }

    /**
     * Synonym for {@link #element(String)}. 
     * 
     * @param name
     * the name of the XML element.
     * 
     * @return
     * a builder node representing the new child.
     * 
     * @throws IllegalStateException
     * if you attempt to add a child element to an XML node that already 
     * contains a text node value.
     */
    public XMLBuilder e(String name) {
        return element(name);
    }
    
    /**
     * Add a named attribute value to the element represented by this builder
     * node, and return the node representing the element to which the 
     * attribute was added (<strong>not</strong> the new attribute node).
     * 
     * @param name
     * the attribute's name.
     * @param value
     * the attribute's value.
     * 
     * @return
     * the builder node representing the element to which the attribute was
     * added.
     */
    public XMLBuilder attribute(String name, String value) {
        xmlElement.setAttribute(name, value);
        return this;
    }

    /**
     * Synonym for {@link #attribute(String, String)}.
     * 
     * @param name
     * the attribute's name.
     * @param value
     * the attribute's value.
     * 
     * @return
     * the builder node representing the element to which the attribute was
     * added.
     */
    public XMLBuilder attr(String name, String value) {
        return attribute(name, value);
    }

    /**
     * Synonym for {@link #attribute(String, String)}.
     * 
     * @param name
     * the attribute's name.
     * @param value
     * the attribute's value.
     * 
     * @return
     * the builder node representing the element to which the attribute was
     * added.
     */
    public XMLBuilder a(String name, String value) {
        return attribute(name, value);
    }

    /**
     * Add a text value to the element represented by this builder node, and 
     * return the node representing the element to which the text 
     * was added (<strong>not</strong> the new text node).
     * 
     * @param value
     * the text value to add to the element.
     * 
     * @return
     * the builder node representing the element to which the text was added.
     */
    public XMLBuilder text(String value) {
        xmlElement.appendChild(getDocument().createTextNode(value));
        return this;
    }

    /**
     * Synonmy for {@link #text(String)}.
     * 
     * @param value
     * the text value to add to the element.
     * 
     * @return
     * the builder node representing the element to which the text was added.
     */
    public XMLBuilder t(String value) {
        return text(value);
    }
    
    /**
     * Add a CDATA value to the element represented by this builder node, and 
     * return the node representing the element to which the data 
     * was added (<strong>not</strong> the new CDATA node).
     * 
     * @param data
     * the data value that will be Base64-encoded and added to a CDATA element.
     * 
     * @return
     * the builder node representing the element to which the data was added.
     */
    public XMLBuilder cdata(byte[] data) {
        xmlElement.appendChild(
            getDocument().createCDATASection(
                Base64.encodeBytes(data, Base64.DONT_BREAK_LINES)));
        return this;
    }

    /**
     * Synonym for {@link #cdata(String)}.
     * 
     * @param data
     * the data value to add to the element.
     * 
     * @return
     * the builder node representing the element to which the data was added.
     */
    public XMLBuilder data(byte[] data) {
        return cdata(data);
    }

    /**
     * Synonym for {@link #cdata(String)}.
     * 
     * @param data
     * the data value to add to the element.
     * 
     * @return
     * the builder node representing the element to which the data was added.
     */
    public XMLBuilder d(byte[] data) {
        return cdata(data);
    }

    /**
     * Add a comment to the element represented by this builder node, and 
     * return the node representing the element to which the comment 
     * was added (<strong>not</strong> the new comment node).
     * 
     * @param comment
     * the comment to add to the element.
     * 
     * @return
     * the builder node representing the element to which the comment was added.
     */
    public XMLBuilder comment(String comment) {
        xmlElement.appendChild(getDocument().createComment(comment));
        return this;
    }

    /**
     * Synonym for {@link #comment(String)}.
     * 
     * @param comment
     * the comment to add to the element.
     * 
     * @return
     * the builder node representing the element to which the comment was added.
     */
    public XMLBuilder cmnt(String comment) {
        return comment(comment);
    }

    /**
     * Synonym for {@link #comment(String)}.
     * 
     * @param comment
     * the comment to add to the element.
     * 
     * @return
     * the builder node representing the element to which the comment was added.
     */
    public XMLBuilder c(String comment) {
        return comment(comment);
    }

    /**
     * Add an instruction to the element represented by this builder node, and 
     * return the node representing the element to which the instruction 
     * was added (<strong>not</strong> the new instruction node).
     * 
     * @param target
     * the target value for the instruction.
     * @param data
     * the data value for the instruction
     * 
     * @return
     * the builder node representing the element to which the instruction was 
     * added.
     */
    public XMLBuilder instruction(String target, String data) {
        xmlElement.appendChild(getDocument().createProcessingInstruction(target, data));
        return this;
    }

    /**
     * Synonym for {@link #instruction(String, String)}.
     * 
     * @param target
     * the target value for the instruction.
     * @param data
     * the data value for the instruction
     * 
     * @return
     * the builder node representing the element to which the instruction was 
     * added.
     */
    public XMLBuilder inst(String target, String data) {
        return instruction(target, data);
    }

    /**
     * Synonym for {@link #instruction(String, String)}.
     * 
     * @param target
     * the target value for the instruction.
     * @param data
     * the data value for the instruction
     * 
     * @return
     * the builder node representing the element to which the instruction was 
     * added.
     */
    public XMLBuilder i(String target, String data) {
        return instruction(target, data);
    }

    /**
     * Add a reference to the element represented by this builder node, and 
     * return the node representing the element to which the reference 
     * was added (<strong>not</strong> the new reference node).
     * 
     * @param name
     * the name value for the reference.
     * 
     * @return
     * the builder node representing the element to which the reference was 
     * added.
     */
    public XMLBuilder reference(String name) {
        xmlElement.appendChild(getDocument().createEntityReference(name));
        return this;
    }

    /**
     * Synonym for {@link #reference(String)}.
     * 
     * @param name
     * the name value for the reference.
     * 
     * @return
     * the builder node representing the element to which the reference was 
     * added.
     */
    public XMLBuilder ref(String name) {
        return reference(name);
    }

    /**
     * Synonym for {@link #reference(String)}.
     * 
     * @param name
     * the name value for the reference.
     * 
     * @return
     * the builder node representing the element to which the reference was 
     * added.
     */
    public XMLBuilder r(String name) {
        return reference(name);
    }

    /**
     * Return the builder node representing the n<em>th</em> ancestor element 
     * of this node, or the root node if n exceeds the document's depth.
     *   
     * @param steps
     * the number of parent elements to step over while navigating up the chain
     * of node ancestors. A steps value of 1 will find a node's parent, 2 will
     * find its grandparent etc.
     * 
     * @return
     * the n<em>th</em> ancestor of this node, or the root node if this is 
     * reached before the n<em>th</em> parent is found.
     */
    public XMLBuilder up(int steps) {
    	Node currNode = (Node) this.xmlElement;
        int stepCount = 0;
        while (currNode.getParentNode() != null && stepCount < steps) {
        	currNode = currNode.getParentNode();
            stepCount++;
        }        
        return new XMLBuilder((Element) currNode, null);
    }
    
    /**
     * Return the builder node representing the parent of the current node.
     * 
     * @return
     * the parent of this node, or the root node if this method is called on the
     * root node. 
     */
    public XMLBuilder up() {
        return up(1);
    }

    /**
     * Serialize the XML document to the given writer using the default 
     * {@link TransformerFactory} and {@link Transformer} classes. If output
     * options are provided, these options are provided to the 
     * {@link Transformer} serializer. 
     * 
     * @param writer
     * a writer to which the serialized document is written.
     * @param outputProperties
     * settings for the {@link Transformer} serializer. This parameter may be
     * null or an empty Properties object, in which case the default output
     * properties will be applied.
     * 
     * @throws TransformerException
     */
    public void toWriter(Writer writer, Properties outputProperties) 
        throws TransformerException 
    {
        StreamResult streamResult = new StreamResult(writer);
        
        DOMSource domSource = new DOMSource(getDocument());
        TransformerFactory tf = TransformerFactory.newInstance();
        Transformer serializer = tf.newTransformer();
        
        if (outputProperties != null) {
            Iterator iter = outputProperties.entrySet().iterator();
            while (iter.hasNext()) {
                Entry entry = (Entry) iter.next();
                serializer.setOutputProperty((String) entry.getKey(), (String) entry.getValue());
            }
        }
        serializer.transform(domSource, streamResult);
    }
    
    /**
     * Serialize the XML document to a string by delegating to the 
     * {@link #toWriter(Writer, Properties)} method. If output options are 
     * provided, these options are provided to the {@link Transformer} 
     * serializer. 
     * 
     * @param outputProperties
     * settings for the {@link Transformer} serializer. This parameter may be
     * null or an empty Properties object, in which case the default output
     * properties will be applied.
     * 
     * @return
     * the XML document as a string
     * 
     * @throws TransformerException 
     */
    public String asString(Properties outputProperties) 
        throws TransformerException 
    {
        StringWriter writer = new StringWriter();
        toWriter(writer, outputProperties);
        return writer.toString();        
    }
    
}