An InputStream backed by a Reader : Reader « File « Java Tutorial

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/*
 * Java Network Programming, Second Edition
 * Merlin Hughes, Michael Shoffner, Derek Hamner
 * Manning Publications Company; ISBN 188477749X
 *
 * http://nitric.com/jnp/
 *
 * Copyright (c) 1997-1999 Merlin Hughes, Michael Shoffner, Derek Hamner;
 * all rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE ABOVE NAMED AUTHORS "AS IS" AND ANY
 * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHORS, THEIR
 * PUBLISHER OR THEIR EMPLOYERS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 */

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStreamWriter;
import java.io.Reader;
import java.io.UnsupportedEncodingException;
import java.io.Writer;

/**
 * An InputStream backed by a Reader
 */
public class ReaderInputStream extends InputStream {
  protected Reader reader;
  protected ByteArrayOutputStream byteArrayOut;
  protected Writer writer;
  protected char[] chars;
  protected byte[] buffer;
  protected int index, length;

  /**
   * Constructor to supply a Reader
   *
   * @param reader - the Reader used by the InputStream
   */
  public ReaderInputStream(Reader reader) {
    this.reader = reader;
    byteArrayOut = new ByteArrayOutputStream();
    writer = new OutputStreamWriter(byteArrayOut);
    chars = new char[1024];
  }

  /**
   * Constructor to supply a Reader and an encoding
   *
   * @param reader   - the Reader used by the InputStream
   * @param encoding - the encoding to use for the InputStream
   * @throws UnsupportedEncodingException if the encoding is not supported
   */
  public ReaderInputStream(Reader reader, String encoding) throws UnsupportedEncodingException {
    this.reader = reader;
    byteArrayOut = new ByteArrayOutputStream();
    writer = new OutputStreamWriter(byteArrayOut, encoding);
    chars = new char[1024];
  }

  /**
   * @see java.io.InputStream#read()
   */
  public int read() throws IOException {
    if (index >= length)
      fillBuffer();
    if (index >= length)
      return -1;
    return 0xff & buffer[index++];
  }

  protected void fillBuffer() throws IOException {
    if (length < 0)
      return;
    int numChars = reader.read(chars);
    if (numChars < 0) {
      length = -1;
    } else {
      byteArrayOut.reset();
      writer.write(chars, 0, numChars);
      writer.flush();
      buffer = byteArrayOut.toByteArray();
      length = buffer.length;
      index = 0;
    }
  }

  /**
   * @see java.io.InputStream#read(byte[], int, int)
   */
  public int read(byte[] data, int off, int len) throws IOException {
    if (index >= length)
      fillBuffer();
    if (index >= length)
      return -1;
    int amount = Math.min(len, length - index);
    System.arraycopy(buffer, index, data, off, amount);
    index += amount;
    return amount;
  }

  /**
   * @see java.io.InputStream#available()
   */
  public int available() throws IOException {
    return (index < length) ? length - index :
        ((length >= 0) && reader.ready()) ? 1 : 0;
  }

  /**
   * @see java.io.InputStream#close()
   */
  public void close() throws IOException {
    reader.close();
  }
}