code: /*
   * 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.io.output;
  
  import java.io.File;
  import java.io.FileNotFoundException;
  import java.io.FileOutputStream;
  import java.io.IOException;
  import java.io.OutputStream;
  import java.io.OutputStreamWriter;
  import java.io.StringWriter;
  import java.io.Writer;
  import java.util.regex.Matcher;
  import java.util.regex.Pattern;
  
  import org.apache.commons.io.input.XmlStreamReader;
  
  /**
   * Character stream that handles all the necessary Voodo to figure out the
   * charset encoding of the XML document written to the stream.
   *
   * @author Herve Boutemy
   * @version $Id: XmlStreamWriter.java,v 1.1.2.1 2011/01/15 20:32:25 caniszczyk Exp $
   * @see XmlStreamReader
   * @since Commons IO 2.0
   */
  public class XmlStreamWriter extends Writer {
      private static final int BUFFER_SIZE = 4096;
  
      private final OutputStream out;
  
      private final String defaultEncoding;
  
      private StringWriter xmlPrologWriter = new StringWriter(BUFFER_SIZE);
  
      private Writer writer;
  
      private String encoding;
  
      /**
       * Construct an new XML stream writer for the specified output stream
       * with a default encoding of UTF-8.
       *
       * @param out The output stream
       */
      public XmlStreamWriter(OutputStream out) {
          this(out, null);
      }
  
      /**
       * Construct an new XML stream writer for the specified output stream
       * with the specified default encoding.
       *
       * @param out The output stream
       * @param defaultEncoding The default encoding if not encoding could be detected
       */
      public XmlStreamWriter(OutputStream out, String defaultEncoding) {
          this.out = out;
          this.defaultEncoding = (defaultEncoding != null ? defaultEncoding : "UTF-8");
      }
  
      /**
       * Construct an new XML stream writer for the specified file
       * with a default encoding of UTF-8.
       * 
       * @param file The file to write to
       * @throws FileNotFoundException if there is an error creating or
       * opening the file
       */
      public XmlStreamWriter(File file) throws FileNotFoundException {
          this(file, null);
      }
  
      /**
       * Construct an new XML stream writer for the specified file
       * with the specified default encoding.
       * 
       * @param file The file to write to
       * @param defaultEncoding The default encoding if not encoding could be detected
       * @throws FileNotFoundException if there is an error creating or
       * opening the file
       */
      public XmlStreamWriter(File file, String defaultEncoding) throws FileNotFoundException {
          this(new FileOutputStream(file), defaultEncoding);
      }
  
      /**
       * Return the detected encoding.
       *
       * @return the detected encoding
       */
      public String getEncoding() {
          return encoding;
      }
  
      /**
       * Return the default encoding.
       *
       * @return the default encoding
       */
      public String getDefaultEncoding() {
          return defaultEncoding;
      }
  
      /**
       * Close the underlying writer.
       *
       * @throws IOException if an error occurs closing the underlying writer
       */
      @Override
      public void close() throws IOException {
          if (writer == null) {
              encoding = defaultEncoding;
              writer = new OutputStreamWriter(out, encoding);
              writer.write(xmlPrologWriter.toString());
          }
          writer.close();
      }
  
      /**
       * Flush the underlying writer.
       *
       * @throws IOException if an error occurs flushing the underlying writer
       */
      @Override
      public void flush() throws IOException {
          if (writer != null) {
              writer.flush();
          }
      }
  
      /**
       * Detect the encoding.
       *
       * @param cbuf the buffer to write the characters from
       * @param off The start offset
       * @param len The number of characters to write
       * @throws IOException if an error occurs detecting the encoding
       */
      private void detectEncoding(char[] cbuf, int off, int len)
              throws IOException {
          int size = len;
          StringBuffer xmlProlog = xmlPrologWriter.getBuffer();
          if (xmlProlog.length() + len > BUFFER_SIZE) {
              size = BUFFER_SIZE - xmlProlog.length();
          }
          xmlPrologWriter.write(cbuf, off, size);
  
          // try to determine encoding
          if (xmlProlog.length() >= 5) {
              if (xmlProlog.substring(0, 5).equals("<?xml")) {
                  // try to extract encoding from XML prolog
                  int xmlPrologEnd = xmlProlog.indexOf("?>");
                  if (xmlPrologEnd > 0) {
                      // ok, full XML prolog written: let's extract encoding
                      Matcher m = ENCODING_PATTERN.matcher(xmlProlog.substring(0,
                              xmlPrologEnd));
                      if (m.find()) {
                          encoding = m.group(1).toUpperCase();
                          encoding = encoding.substring(1, encoding.length() - 1);
                      } else {
                          // no encoding found in XML prolog: using default
                          // encoding
                          encoding = defaultEncoding;
                      }
                  } else {
                      if (xmlProlog.length() >= BUFFER_SIZE) {
                          // no encoding found in first characters: using default
                          // encoding
                          encoding = defaultEncoding;
                      }
                  }
              } else {
                  // no XML prolog: using default encoding
                  encoding = defaultEncoding;
              }
              if (encoding != null) {
                  // encoding has been chosen: let's do it
                  xmlPrologWriter = null;
                  writer = new OutputStreamWriter(out, encoding);
                  writer.write(xmlProlog.toString());
                  if (len > size) {
                      writer.write(cbuf, off + size, len - size);
                  }
              }
          }
      }
  
      /**
       * Write the characters to the underlying writer, detecing encoding.
       * 
       * @param cbuf the buffer to write the characters from
       * @param off The start offset
       * @param len The number of characters to write
       * @throws IOException if an error occurs detecting the encoding
       */
      @Override
      public void write(char[] cbuf, int off, int len) throws IOException {
          if (xmlPrologWriter != null) {
              detectEncoding(cbuf, off, len);
          } else {
              writer.write(cbuf, off, len);
          }
      }
  
      static final Pattern ENCODING_PATTERN = XmlStreamReader.ENCODING_PATTERN;
  }
  