Traverse a DOM tree in order to print a document that is parsed : DOM Tree « XML « Java Tutorial

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// $Id: DOMWriter.java 2891 2008-07-31 16:03:02Z thomas.diesler@jboss.com $
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.io.StringWriter;
import java.io.UnsupportedEncodingException;
import java.io.Writer;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

import org.w3c.dom.Attr;
import org.w3c.dom.Element;
import org.w3c.dom.NamedNodeMap;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

/**
 * Traverse a DOM tree in order to print a document that is parsed.
 * 
 * @author Andy Clark, IBM
 * @author Thomas.Diesler@jboss.org
 */
@SuppressWarnings("unchecked")
public class DOMWriter {
  // Print writer
  private PrintWriter out;

  // True, if canonical output
  private boolean canonical;

  // True, if pretty printing should be used
  private boolean prettyprint;

  // True, if the XML declaration should be written
  private boolean writeXMLDeclaration;

  // True, if whitespace should be ignored
  private boolean ignoreWhitespace;

  // Explicit character set encoding
  private String charsetName;

  // indent for the pretty printer
  private int prettyIndent;

  // True, if the XML declaration has been written
  private boolean wroteXMLDeclaration;

  // The node that started the write
  private Node rootNode;

  // True if we want namespace completion
  private boolean completeNamespaces = true;

  // The current default namespace
  private String currentDefaultNamespace;

  public DOMWriter(Writer w) {
    this.out = new PrintWriter(w);
  }

  public DOMWriter(Writer w, String charsetName) {
    this.out = new PrintWriter(w);
    this.charsetName = charsetName;
    this.writeXMLDeclaration = true;
  }

  public DOMWriter(OutputStream stream) {
    try {
      this.out = new PrintWriter(new OutputStreamWriter(stream, "UTF-8"));
    } catch (UnsupportedEncodingException e) {
      // ignore, UTF-8 should be available
    }
  }

  public DOMWriter(OutputStream stream, String charsetName) {
    try {
      this.out = new PrintWriter(new OutputStreamWriter(stream, charsetName));
      this.charsetName = charsetName;
      this.writeXMLDeclaration = true;
    } catch (UnsupportedEncodingException e) {
      throw new IllegalArgumentException("Unsupported encoding: " + charsetName);
    }
  }

  /**
   * Print a node with explicit prettyprinting. The defaults for all other
   * DOMWriter properties apply.
   * 
   */
  public static String printNode(Node node, boolean prettyprint) {
    StringWriter strw = new StringWriter();
    new DOMWriter(strw).setPrettyprint(prettyprint).print(node);
    return strw.toString();
  }

  public boolean isCanonical() {
    return canonical;
  }

  /**
   * Set wheter entities should appear in their canonical form. The default is
   * false.
   */
  public DOMWriter setCanonical(boolean canonical) {
    this.canonical = canonical;
    return this;
  }

  public boolean isIgnoreWhitespace() {
    return ignoreWhitespace;
  }

  /**
   * Set whether whitespace should be ignored. The default is false.
   */
  public DOMWriter setIgnoreWhitespace(boolean ignoreWhitespace) {
    this.ignoreWhitespace = ignoreWhitespace;
    return this;
  }

  /**
   * Set wheter subelements should have their namespaces completed. Setting this
   * to false may lead to invalid XML fragments. The default is true.
   */
  public DOMWriter setCompleteNamespaces(boolean complete) {
    this.completeNamespaces = complete;
    return this;
  }

  public boolean isPrettyprint() {
    return prettyprint;
  }

  /**
   * Set wheter element should be indented. The default is false.
   */
  public DOMWriter setPrettyprint(boolean prettyprint) {
    this.prettyprint = prettyprint;
    return this;
  }

  public boolean isWriteXMLDeclaration() {
    return writeXMLDeclaration;
  }

  /**
   * Set wheter the XML declaration should be written. The default is false.
   */
  public DOMWriter setWriteXMLDeclaration(boolean flag) {
    this.writeXMLDeclaration = flag;
    return this;
  }

  public void print(Node node) {
    if (prettyprint && ignoreWhitespace)
      throw new IllegalStateException("Cannot pretty print and ignore whitespace");

    rootNode = node;
    printInternal(node, false);
  }

  private void printInternal(Node node, boolean indentEndMarker) {
    // is there anything to do?
    if (node == null) {
      return;
    }

    // JBAS-2117 - Don't skip the DOCUMENT_NODE
    // if (node instanceof Document) node =
    // ((Document)node).getDocumentElement();

    if (wroteXMLDeclaration == false && writeXMLDeclaration == true && canonical == false) {
      out.print("<?xml version='1.0'");
      if (charsetName != null)
        out.print(" encoding='" + charsetName + "'");

      out.print("?>");
      if (prettyprint)
        out.println();

      wroteXMLDeclaration = true;
    }

    int type = node.getNodeType();
    boolean hasChildNodes = node.getChildNodes().getLength() > 0;

    String nodeName = node.getNodeName();
    switch (type) {
    // print document
    case Node.DOCUMENT_NODE: {
      NodeList children = node.getChildNodes();
      for (int iChild = 0; iChild < children.getLength(); iChild++) {
        printInternal(children.item(iChild), false);
      }
      out.flush();
      break;
    }

    // print element with attributes
    case Node.ELEMENT_NODE: {
      Element element = (Element) node;
      if (prettyprint) {
        for (int i = 0; i < prettyIndent; i++) {
          out.print(' ');
        }
        prettyIndent++;
      }

      out.print('<');
      out.print(nodeName);

      Map nsMap = new HashMap();
      String elPrefix = node.getPrefix();
      String elNamespaceURI = node.getNamespaceURI();
      if (elPrefix != null) {
        String nsURI = getNamespaceURI(elPrefix, element, rootNode);
        nsMap.put(elPrefix, nsURI);
      }

      Attr attrs[] = sortAttributes(node.getAttributes());
      for (int i = 0; i < attrs.length; i++) {
        Attr attr = attrs[i];
        String atPrefix = attr.getPrefix();
        String atName = attr.getNodeName();
        String atValue = normalize(attr.getNodeValue(), canonical);

        if (atName.equals("xmlns"))
          currentDefaultNamespace = atValue;

        if (atPrefix != null && !atPrefix.equals("xmlns") && !atPrefix.equals("xml")) {
          String nsURI = getNamespaceURI(atPrefix, element, rootNode);
          nsMap.put(atPrefix, nsURI);
          // xsi:type='ns1:SubType', xsi:type='xsd:string'
          if (atName.equals(atPrefix + ":type") && atValue.indexOf(":") > 0) {
            // xsi defined on the envelope
            if (nsURI == null)
              nsURI = getNamespaceURI(atPrefix, element, null);

            if ("http://www.w3.org/2001/XMLSchema-instance".equals(nsURI)) {
              String typePrefix = atValue.substring(0, atValue.indexOf(":"));
              String typeURI = getNamespaceURI(typePrefix, element, rootNode);
              nsMap.put(typePrefix, typeURI);
            }
          }
        }

        out.print(" " + atName + "='" + atValue + "'");
      }

      // Add namespace declaration for prefixes
      // that are defined further up the tree
      if (completeNamespaces) {
        Iterator itPrefix = nsMap.keySet().iterator();
        while (itPrefix.hasNext()) {
          String prefix = (String) itPrefix.next();
          String nsURI = (String) nsMap.get(prefix);
          if (nsURI == null) {
            nsURI = getNamespaceURI(prefix, element, null);
            out.print(" xmlns:" + prefix + "='" + nsURI + "'");
          }
        }
      }

      // The SAX ContentHandler will by default not add the namespace
      // declaration
      // <Hello xmlns='http://somens'>World</Hello>
      if (elPrefix == null && elNamespaceURI != null) {
        String defaultNamespace = element.getAttribute("xmlns");
        if (defaultNamespace.length() == 0 && !elNamespaceURI.equals(currentDefaultNamespace)) {
          out.print(" xmlns='" + elNamespaceURI + "'");
          currentDefaultNamespace = elNamespaceURI;
        }
      }

      if (hasChildNodes) {
        out.print('>');
      }

      // Find out if the end marker is indented
      indentEndMarker = isEndMarkerIndented(node);

      if (indentEndMarker) {
        out.print('\n');
      }

      NodeList childNodes = node.getChildNodes();
      int len = childNodes.getLength();
      for (int i = 0; i < len; i++) {
        Node childNode = childNodes.item(i);
        printInternal(childNode, false);
      }
      break;
    }

    // handle entity reference nodes
    case Node.ENTITY_REFERENCE_NODE: {
      if (canonical) {
        NodeList children = node.getChildNodes();
        if (children != null) {
          int len = children.getLength();
          for (int i = 0; i < len; i++) {
            printInternal(children.item(i), false);
          }
        }
      } else {
        out.print('&');
        out.print(nodeName);
        out.print(';');
      }
      break;
    }

    // print cdata sections
    case Node.CDATA_SECTION_NODE: {
      if (canonical) {
        out.print(normalize(node.getNodeValue(), canonical));
      } else {
        out.print("<![CDATA[");
        out.print(node.getNodeValue());
        out.print("]]&gt;");
      }
      break;
    }

    // print text
    case Node.TEXT_NODE: {
      String text = normalize(node.getNodeValue(), canonical);
      if (text.trim().length() > 0) {
        out.print(text);
      } else if (prettyprint == false && ignoreWhitespace == false) {
        out.print(text);
      }
      break;
    }

    // print processing instruction
    case Node.PROCESSING_INSTRUCTION_NODE: {
      out.print("<?");
      out.print(nodeName);
      String data = node.getNodeValue();
      if (data != null && data.length() > 0) {
        out.print(' ');
        out.print(data);
      }
      out.print("?>");
      break;
    }

    // print comment
    case Node.COMMENT_NODE: {
      for (int i = 0; i < prettyIndent; i++) {
        out.print(' ');
      }

      out.print("<!--");
      String data = node.getNodeValue();
      if (data != null) {
        out.print(data);
      }
      out.print("-->");

      if (prettyprint) {
        out.print('\n');
      }

      break;
    }
    }

    if (type == Node.ELEMENT_NODE) {
      if (prettyprint)
        prettyIndent--;

      if (hasChildNodes == false) {
        out.print("/>");
      } else {
        if (indentEndMarker) {
          for (int i = 0; i < prettyIndent; i++) {
            out.print(' ');
          }
        }

        out.print("</");
        out.print(nodeName);
        out.print('>');
      }

      if (prettyIndent > 0) {
        out.print('\n');
      }
    }
    out.flush();
  }

  private String getNamespaceURI(String prefix, Element element, Node stopNode) {
    Node parent = element.getParentNode();
    String nsURI = element.getAttribute("xmlns:" + prefix);
    if (nsURI.length() == 0 && element != stopNode && parent instanceof Element)
      return getNamespaceURI(prefix, (Element) parent, stopNode);

    return (nsURI.length() > 0 ? nsURI : null);
  }

  private boolean isEndMarkerIndented(Node node) {
    if (prettyprint) {
      NodeList childNodes = node.getChildNodes();
      int len = childNodes.getLength();
      for (int i = 0; i < len; i++) {
        Node children = childNodes.item(i);
        if (children.getNodeType() == Node.ELEMENT_NODE) {
          return true;
        }
      }
    }
    return false;
  }

  /** Returns a sorted list of attributes. */
  private Attr[] sortAttributes(NamedNodeMap attrs) {

    int len = (attrs != null) ? attrs.getLength() : 0;
    Attr array[] = new Attr[len];
    for (int i = 0; i < len; i++) {
      array[i] = (Attr) attrs.item(i);
    }
    for (int i = 0; i < len - 1; i++) {
      String name = array[i].getNodeName();
      int index = i;
      for (int j = i + 1; j < len; j++) {
        String curName = array[j].getNodeName();
        if (curName.compareTo(name) < 0) {
          name = curName;
          index = j;
        }
      }
      if (index != i) {
        Attr temp = array[i];
        array[i] = array[index];
        array[index] = temp;
      }
    }
    return (array);
  }

  /** Normalizes the given string. */
  public static String normalize(String s, boolean canonical) {
    StringBuffer str = new StringBuffer();

    int len = (s != null) ? s.length() : 0;
    for (int i = 0; i < len; i++) {
      char ch = s.charAt(i);
      switch (ch) {
      case '<': {
        str.append("&lt;");
        break;
      }
      case '>': {
        str.append("&gt;");
        break;
      }
      case '&': {
        str.append("&amp;");
        break;
      }
      case '"': {
        str.append("&quot;");
        break;
      }
      case '\'': {
        str.append("&apos;");
        break;
      }
      case '\r':
      case '\n': {
        if (canonical) {
          str.append("&#");
          str.append(Integer.toString(ch));
          str.append(';');
          break;
        }
        // else, default append char
      }
      default: {
        str.append(ch);
      }
      }
    }
    return (str.toString());
  }
}