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.ByteArrayInputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.OutputStream;
  import java.io.SequenceInputStream;
  import java.io.UnsupportedEncodingException;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.List;
  
  import org.apache.commons.io.input.ClosedInputStream;
  
  /**
   * This class implements an output stream in which the data is 
   * written into a byte array. The buffer automatically grows as data 
   * is written to it.
   * <p> 
   * The data can be retrieved using <code>toByteArray()</code> and
   * <code>toString()</code>.
   * <p>
   * Closing a <tt>ByteArrayOutputStream</tt> has no effect. The methods in
   * this class can be called after the stream has been closed without
   * generating an <tt>IOException</tt>.
   * <p>
   * This is an alternative implementation of the java.io.ByteArrayOutputStream
   * class. The original implementation only allocates 32 bytes at the beginning.
   * As this class is designed for heavy duty it starts at 1024 bytes. In contrast
   * to the original it doesn't reallocate the whole memory block but allocates
   * additional buffers. This way no buffers need to be garbage collected and
   * the contents don't have to be copied to the new buffer. This class is
   * designed to behave exactly like the original. The only exception is the
   * deprecated toString(int) method that has been ignored.
   * 
   * @author <a href="mailto:jeremias@apache.org">Jeremias Maerki</a>
   * @author Holger Hoffstatte
   * @version $Id: ByteArrayOutputStream.java 1021884 2010-10-12 18:49:16Z ggregory $
   */
  public class ByteArrayOutputStream extends OutputStream {
  
      /** A singleton empty byte array. */
      private static final byte[] EMPTY_BYTE_ARRAY = new byte[0];
  
      /** The list of buffers, which grows and never reduces. */
      private final List<byte[]> buffers = new ArrayList<byte[]>();
      /** The index of the current buffer. */
      private int currentBufferIndex;
      /** The total count of bytes in all the filled buffers. */
      private int filledBufferSum;
      /** The current buffer. */
      private byte[] currentBuffer;
      /** The total count of bytes written. */
      private int count;
  
      /**
       * Creates a new byte array output stream. The buffer capacity is 
       * initially 1024 bytes, though its size increases if necessary. 
       */
      public ByteArrayOutputStream() {
          this(1024);
      }
  
      /**
       * Creates a new byte array output stream, with a buffer capacity of 
       * the specified size, in bytes. 
       *
       * @param size  the initial size
       * @throws IllegalArgumentException if size is negative
       */
      public ByteArrayOutputStream(int size) {
          if (size < 0) {
              throw new IllegalArgumentException(
                  "Negative initial size: " + size);
          }
          synchronized (this) {
              needNewBuffer(size);
          }
      }
  
      /**
       * Makes a new buffer available either by allocating
       * a new one or re-cycling an existing one.
       *
       * @param newcount  the size of the buffer if one is created
       */
      private void needNewBuffer(int newcount) {
          if (currentBufferIndex < buffers.size() - 1) {
              //Recycling old buffer
              filledBufferSum += currentBuffer.length;
              
              currentBufferIndex++;
              currentBuffer = buffers.get(currentBufferIndex);
          } else {
              //Creating new buffer
              int newBufferSize;
              if (currentBuffer == null) {
                  newBufferSize = newcount;
                  filledBufferSum = 0;
              } else {
                  newBufferSize = Math.max(
                      currentBuffer.length << 1, 
                      newcount - filledBufferSum);
                  filledBufferSum += currentBuffer.length;
              }
              
              currentBufferIndex++;
              currentBuffer = new byte[newBufferSize];
              buffers.add(currentBuffer);
          }
      }
  
      /**
       * Write the bytes to byte array.
       * @param b the bytes to write
       * @param off The start offset
       * @param len The number of bytes to write
       */
      @Override
      public void write(byte[] b, int off, int len) {
          if ((off < 0) 
                  || (off > b.length) 
                  || (len < 0) 
                  || ((off + len) > b.length) 
                  || ((off + len) < 0)) {
              throw new IndexOutOfBoundsException();
          } else if (len == 0) {
              return;
          }
          synchronized (this) {
              int newcount = count + len;
              int remaining = len;
              int inBufferPos = count - filledBufferSum;
              while (remaining > 0) {
                  int part = Math.min(remaining, currentBuffer.length - inBufferPos);
                  System.arraycopy(b, off + len - remaining, currentBuffer, inBufferPos, part);
                  remaining -= part;
                  if (remaining > 0) {
                      needNewBuffer(newcount);
                      inBufferPos = 0;
                  }
              }
              count = newcount;
          }
      }
  
      /**
       * Write a byte to byte array.
       * @param b the byte to write
       */
      @Override
      public synchronized void write(int b) {
          int inBufferPos = count - filledBufferSum;
          if (inBufferPos == currentBuffer.length) {
              needNewBuffer(count + 1);
              inBufferPos = 0;
          }
          currentBuffer[inBufferPos] = (byte) b;
          count++;
      }
  
      /**
       * Writes the entire contents of the specified input stream to this
       * byte stream. Bytes from the input stream are read directly into the
       * internal buffers of this streams.
       *
       * @param in the input stream to read from
       * @return total number of bytes read from the input stream
       *         (and written to this stream)
       * @throws IOException if an I/O error occurs while reading the input stream
       * @since Commons IO 1.4
       */
      public synchronized int write(InputStream in) throws IOException {
          int readCount = 0;
          int inBufferPos = count - filledBufferSum;
          int n = in.read(currentBuffer, inBufferPos, currentBuffer.length - inBufferPos);
          while (n != -1) {
              readCount += n;
              inBufferPos += n;
              count += n;
              if (inBufferPos == currentBuffer.length) {
                  needNewBuffer(currentBuffer.length);
                  inBufferPos = 0;
              }
              n = in.read(currentBuffer, inBufferPos, currentBuffer.length - inBufferPos);
          }
          return readCount;
      }
  
      /**
       * Return the current size of the byte array.
       * @return the current size of the byte array
       */
      public synchronized int size() {
          return count;
      }
  
      /**
       * Closing a <tt>ByteArrayOutputStream</tt> has no effect. The methods in
       * this class can be called after the stream has been closed without
       * generating an <tt>IOException</tt>.
       *
       * @throws IOException never (this method should not declare this exception
       * but it has to now due to backwards compatability)
       */
      @Override
      public void close() throws IOException {
          //nop
      }
  
      /**
       * @see java.io.ByteArrayOutputStream#reset()
       */
      public synchronized void reset() {
          count = 0;
          filledBufferSum = 0;
          currentBufferIndex = 0;
          currentBuffer = buffers.get(currentBufferIndex);
      }
  
      /**
       * Writes the entire contents of this byte stream to the
       * specified output stream.
       *
       * @param out  the output stream to write to
       * @throws IOException if an I/O error occurs, such as if the stream is closed
       * @see java.io.ByteArrayOutputStream#writeTo(OutputStream)
       */
      public synchronized void writeTo(OutputStream out) throws IOException {
          int remaining = count;
          for (byte[] buf : buffers) {
              int c = Math.min(buf.length, remaining);
              out.write(buf, 0, c);
              remaining -= c;
              if (remaining == 0) {
                  break;
              }
          }
      }
  
      /**
       * Fetches entire contents of an <code>InputStream</code> and represent
       * same data as result InputStream.
       * <p>
       * This method is useful where,
       * <ul>
       * <li>Source InputStream is slow.</li>
       * <li>It has network resources associated, so we cannot keep it open for
       * long time.</li>
       * <li>It has network timeout associated.</li>
       * </ul>
       * It can be used in favor of {@link #toByteArray()}, since it
       * avoids unnecessary allocation and copy of byte[].<br>
       * This method buffers the input internally, so there is no need to use a
       * <code>BufferedInputStream</code>.
       * 
       * @param input Stream to be fully buffered.
       * @return A fully buffered stream.
       * @throws IOException if an I/O error occurs
       * @since Commons IO 2.0
       */
      public static InputStream toBufferedInputStream(InputStream input)
              throws IOException {
          ByteArrayOutputStream output = new ByteArrayOutputStream();
          output.write(input);
          return output.toBufferedInputStream();
      }
  
      /**
       * Gets the current contents of this byte stream as a Input Stream. The
       * returned stream is backed by buffers of <code>this</code> stream,
       * avoiding memory allocation and copy, thus saving space and time.<br>
       * 
       * @return the current contents of this output stream.
       * @see java.io.ByteArrayOutputStream#toByteArray()
       * @see #reset()
       * @since Commons IO 2.0
       */
      private InputStream toBufferedInputStream() {
          int remaining = count;
          if (remaining == 0) {
              return new ClosedInputStream();
          }
          List<ByteArrayInputStream> list = new ArrayList<ByteArrayInputStream>(buffers.size());
          for (byte[] buf : buffers) {
              int c = Math.min(buf.length, remaining);
              list.add(new ByteArrayInputStream(buf, 0, c));
              remaining -= c;
              if (remaining == 0) {
                  break;
              }
          }
          return new SequenceInputStream(Collections.enumeration(list));
      }
  
      /**
       * Gets the curent contents of this byte stream as a byte array.
       * The result is independent of this stream.
       *
       * @return the current contents of this output stream, as a byte array
       * @see java.io.ByteArrayOutputStream#toByteArray()
       */
      public synchronized byte[] toByteArray() {
          int remaining = count;
          if (remaining == 0) {
              return EMPTY_BYTE_ARRAY; 
          }
          byte newbuf[] = new byte[remaining];
          int pos = 0;
          for (byte[] buf : buffers) {
              int c = Math.min(buf.length, remaining);
              System.arraycopy(buf, 0, newbuf, pos, c);
              pos += c;
              remaining -= c;
              if (remaining == 0) {
                  break;
              }
          }
          return newbuf;
      }
  
      /**
       * Gets the curent contents of this byte stream as a string.
       * @return the contents of the byte array as a String
       * @see java.io.ByteArrayOutputStream#toString()
       */
      @Override
      public String toString() {
          return new String(toByteArray());
      }
  
      /**
       * Gets the curent contents of this byte stream as a string
       * using the specified encoding.
       *
       * @param enc  the name of the character encoding
       * @return the string converted from the byte array
       * @throws UnsupportedEncodingException if the encoding is not supported
       * @see java.io.ByteArrayOutputStream#toString(String)
       */
      public String toString(String enc) throws UnsupportedEncodingException {
          return new String(toByteArray(), enc);
      }
  
  }
  