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The core XML data binding framework with support for marshalling Java objects to and unmarshalling from XML documents.
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/*
 * Copyright 2011 Jakub Narloch
 *
 * 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.
 */
package org.exolab.castor.xml.util;

import java.util.Enumeration;

import javax.xml.stream.XMLStreamException;
import javax.xml.stream.XMLStreamWriter;

import org.castor.core.util.Assert;
import org.exolab.castor.xml.NamespacesStack;
import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;

/**
 * A document handler that uses internally a instance of {@link XMLStreamWriter} to output the
 * result xml.
 *
 * @author Jakub Narloch
 * @version 1.3.3
 * @since 1.3.3
 */
public class StaxStreamHandler extends DefaultHandler {

  /**
   * Represents the instance of {@link XMLStreamWriter} class, that will be used to output the
   * marshalled object.
   */
  private final XMLStreamWriter xmlStreamWriter;

  /**
   * Instance of {@link org.exolab.castor.xml.Namespaces} used for handling the namespace.
   */
  private NamespacesStack namespacesStack = new NamespacesStack();

  /**
   * Flag indicating whether the new namespace scope is required to create.
   */
  private boolean createNamespaceScope = true;

  /**
   * Creates new instance of {@link StaxStreamHandler} class.
   *
   * @param xmlStreamWriter the instance of {@link XMLStreamWriter} to use
   *
   * @throws IllegalArgumentException if xmlStreamWriter is null
   */
  public StaxStreamHandler(XMLStreamWriter xmlStreamWriter) {
    Assert.paramNotNull(xmlStreamWriter, "xmlStreamWriter");

    this.xmlStreamWriter = xmlStreamWriter;
  }

  @Override
  public void startDocument() throws SAXException {
    try {
      xmlStreamWriter.writeStartDocument();
    } catch (XMLStreamException e) {
      convertToSAXException("Error occurred when writing the document start.", e);
    }
  }

  @Override
  public void endDocument() throws SAXException {
    try {
      xmlStreamWriter.writeEndDocument();
      xmlStreamWriter.flush();
    } catch (XMLStreamException e) {
      convertToSAXException("Error occurred when writing the document end.", e);
    }
  }

  @Override
  public void startPrefixMapping(String prefix, String uri) throws SAXException {
    if (createNamespaceScope) {
      namespacesStack.addNewNamespaceScope();
      createNamespaceScope = false;
    }

    namespacesStack.addNamespace(prefix, uri);
  }

  @Override
  public void startElement(String uri, String localName, String qName, Attributes attributes)
      throws SAXException {
    try {
      // writes the element start
      xmlStreamWriter.writeStartElement(qName);

      // iterates through all attributes and writes them
      for (int i = 0; i < attributes.getLength(); i++) {
        xmlStreamWriter.writeAttribute(attributes.getQName(i), attributes.getValue(i));
      }

      // retrieves the default namespace
      String defaultNamespace = namespacesStack.getDefaultNamespaceURI();
      if (defaultNamespace != null && defaultNamespace.length() > 0) {
        xmlStreamWriter.setDefaultNamespace(defaultNamespace);
      }

      // iterates over all namespaces declared in current scope
      Enumeration enumeration = namespacesStack.getLocalNamespacePrefixes();
      String prefix;
      while (enumeration.hasMoreElements()) {
        prefix = (String) enumeration.nextElement();
        xmlStreamWriter.writeNamespace(prefix, namespacesStack.getNamespaceURI(prefix));
      }
    } catch (XMLStreamException e) {
      convertToSAXException("Error occurred when writing the element start.", e);
    }
  }

  @Override
  public void endElement(String uri, String localName, String qName) throws SAXException {
    try {
      // writes the element end
      xmlStreamWriter.writeEndElement();
    } catch (XMLStreamException e) {
      convertToSAXException("Error occurred when writing the element end.", e);
    }
  }

  @Override
  public void ignorableWhitespace(char[] ch, int start, int length) throws SAXException {
    try {
      // writes the characters to output xml
      xmlStreamWriter.writeCharacters(ch, start, length);
    } catch (XMLStreamException e) {
      convertToSAXException("Error occurred when writing the white spaces.", e);
    }
  }

  @Override
  public void characters(char[] ch, int start, int length) throws SAXException {
    try {
      // writes the characters to output xml
      xmlStreamWriter.writeCharacters(ch, start, length);
    } catch (XMLStreamException e) {
      convertToSAXException("Error occurred when writing the characters.", e);
    }
  }

  @Override
  public void processingInstruction(String target, String data) throws SAXException {
    try {
      // writes the processing instruction
      xmlStreamWriter.writeProcessingInstruction(target, data);
    } catch (XMLStreamException e) {
      convertToSAXException("Error occurred when writing the processing instruction.", e);
    }
  }

  /**
   * Converts the passed exception into a {@link SAXException} instance with using the provided
   * error message and exception cause.
   *
   * @param msg the error message
   * @param e the inner cause of newly created exception
   *
   * @throws SAXException the newly created exception instance
   */
  private void convertToSAXException(String msg, XMLStreamException e) throws SAXException {
    throw new SAXException(msg, e);
  }
}