/src/com/topologi/diffx/xml/XMLIndenter.java

/*

 * This file is part of the DiffX library.

 *

 * For licensing information please see the file license.txt included in the release.

 * A copy of this licence can also be found at

 *   http://www.opensource.org/licenses/artistic-license-2.0.php

 */

package com.topologi.diffx.xml;



import java.io.IOException;

import java.io.PrintWriter;

import java.io.Reader;

import java.io.StringReader;

import java.io.StringWriter;

import java.io.Writer;

import java.util.Stack;



import javax.xml.parsers.ParserConfigurationException;

import javax.xml.parsers.SAXParserFactory;



import org.xml.sax.Attributes;

import org.xml.sax.ContentHandler;

import org.xml.sax.InputSource;

import org.xml.sax.SAXException;

import org.xml.sax.XMLReader;

import org.xml.sax.helpers.DefaultHandler;



/**

 * A class to indent automatically some XML data.

 *

 * <p>Note: This implementation is not namespace aware, and will not handle entities other than

 * &amp;amp;, &amp;lt;, &amp;gt; or &amp;quot;.

 *

 * @author Christophe Lauret - Allette Systems (Australia)

 * @version 26 February 2005

 */

public final class XMLIndenter extends DefaultHandler implements ContentHandler {



  /**

   * The writer where the XML goes.

   */

  private final PrintWriter writer;



  // state attributes ---------------------------------------------------------------------------



  /**

   * The indentation level.

   */

  private transient int indentLevel = 0;



  /**

   * The stack of states

   */

  private transient Stack<Integer> states = new Stack<Integer>();



  /**

   * Element has neither text, nor children.

   */

  private static final Integer EMPTY = new Integer(0);



  /**

   * Element has text.

   */

  private static final Integer HAS_TEXT = new Integer(1);



  /**

   * Element has children.

   */

  private static final Integer HAS_CHILDREN = new Integer(2);



  /* ----------------------------------------- constructor --------------------------------------- */



  /**

   * Creates a new XML Indenter.

   *

   * @param w The writer to use.

   */

  private XMLIndenter(Writer w) {

    if (w instanceof PrintWriter) {

      this.writer = (PrintWriter) w;

    } else {

      this.writer = new PrintWriter(w);

    }

  }



  /* -------------------------------------- handler's methods ------------------------------------ */



  /**

   * {@inheritDoc}

   */

  @Override

  public void startElement(String uri, String localName, String qName, Attributes atts) {

    // update the state of previous element

    if (!this.states.empty()) {

      if (this.states.pop().equals(EMPTY)) {

        this.writer.println('>');

      }

      this.states.push(HAS_CHILDREN);

    }

    // always indent

    for (int i = 0; i < this.indentLevel; i++) {

      this.writer.print("  ");

    }

    // print XML data

    this.writer.print('<' + qName);

    for (int i = 0; i < atts.getLength(); i++) {

      this.writer.print(' '+atts.getQName(i)+"=\""+atts.getValue(i)+'"');

    }

    // update attributes

    this.indentLevel++;

    this.states.push(EMPTY);

  }



  /**

   * {@inheritDoc}

   */

  @Override

  public void endElement(String uri, String localName, String qName) {

    this.indentLevel--;

    Object state = this.states.pop();

    if (EMPTY.equals(state)) {

      this.writer.println("/>");

    } else if (HAS_TEXT.equals(state)) {

      this.writer.println("</" + qName + '>');

    } else if (HAS_CHILDREN.equals(state)) {

      for (int i = 0; i < this.indentLevel; i++) {

        this.writer.print("  ");

      }

      this.writer.println("</" + qName + '>');

    }

  }



  /**

   * Prints the characters.

   *

   * {@inheritDoc}

   */

  @Override

  public void characters(char[] ch, int position, int offset) {

    if (this.states.peek().equals(EMPTY)) {

      this.states.pop();

      this.writer.print('>');

      this.states.push(HAS_TEXT);

    }

    this.writer.print(new String(ch, position, offset));

  }



  /**

   * Does nothing.

   *

   * {@inheritDoc}

   */

  @Override

  public void ignorableWhitespace(char[] ch, int position, int offset) {

    // do nothing.

  }



  /* ---------------------------------------- static methods ------------------------------------- */



  /**

   * Indents the given XML String.

   *

   * @param xml The XML string to indent

   *

   * @return The indented XML String.

   *

   * @throws IOException If an IOException occurs.

   * @throws SAXException If the XML is not well-formed.

   * @throws ParserConfigurationException If the parser could not be configured

   */

  public static String indent(String xml)

      throws SAXException, IOException, ParserConfigurationException {

    Writer writer = new StringWriter();

    Reader reader = new StringReader(xml);

    indent(reader, writer);

    return writer.toString();

  }



  /**

   * Indents the given XML String.

   *

   * @param r A reader on XML data

   * @param w A writer for the indented XML

   *

   * @throws IOException If an IOException occurs.

   * @throws SAXException If the XML is not well-formed.

   * @throws ParserConfigurationException If the parser could not be configured

   */

  public static void indent(Reader r, Writer w)

      throws SAXException, IOException, ParserConfigurationException {

    // create the indenter

    XMLIndenter indenter = new XMLIndenter(w);

    // initialise the SAX framework

    SAXParserFactory factory = SAXParserFactory.newInstance();

    factory.setNamespaceAware(false);

    factory.setValidating(false);

    InputSource source = new InputSource(r);

    // parse the XML

    XMLReader xmlreader = factory.newSAXParser().getXMLReader();

    xmlreader.setContentHandler(indenter);

    xmlreader.parse(source);

  }



  /**

   * Indents the given XML String.

   *

   * @param xml The XML string to indent

   *

   * @return The indented XML String or <code>null</code> if an error occurred.

   */

  public static String indentSilent(String xml) {

    try {

      return indent(xml);

    } catch (Exception ex) {

      return null;

    }

  }



  /**

   * Indents the given XML String.

   *

   * <p>This method does not throw any exception out of convenience, instead it returns a

   * <code>boolean</code> value to indicate whether the XML indenting was performed succesfully.

   *

   * @param r A reader on XML data

   * @param w A writer for the indented XML

   *

   * @return <code>true</code> if the operation was successful, <code>false</code> if an error

   *         occurred.

   */

  public static boolean indentSilent(Reader r, Writer w) {

    try {

      indent(r, w);

      return true;

    } catch (Exception ex) {

      return false;

    }

  }



}