A string writer that is able to write large amounts of data. : Writer « File « Java Tutorial

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/**
 * 
 * JFreeReport : a free Java reporting library
 * 
 *
 * Project Info:  http://reporting.pentaho.org/
 *
 * (C) Copyright 2001-2007, by Object Refinery Ltd, Pentaho Corporation and Contributors.
 *
 * This library is free software; you can redistribute it and/or modify it under the terms
 * of the GNU Lesser General Public License as published by the Free Software Foundation;
 * either version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
 * without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License along with this
 * library; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330,
 * Boston, MA 02111-1307, USA.
 *
 * [Java is a trademark or registered trademark of Sun Microsystems, Inc.
 * in the United States and other countries.]
 *
 * ------------
 * MemoryStringWriter.java
 * ------------
 * (C) Copyright 2001-2007, by Object Refinery Ltd, Pentaho Corporation and Contributors.
 */

import java.io.IOException;
import java.io.Writer;

/**
 * A string writer that is able to write large amounts of data. The original
 * StringWriter contained in Java doubles its buffersize everytime the buffer
 * overflows. This is nice with small amounts of data, but awfull for huge
 * buffers.
 * 
 * @author Thomas Morgner
 */
public class MemoryStringWriter extends Writer {
  private int bufferIncrement;

  private int cursor;

  private char[] buffer;

  private int maximumBufferIncrement;

  /**
   * Create a new character-stream writer whose critical sections will
   * synchronize on the writer itself.
   */
  public MemoryStringWriter() {
    this(4096);
  }

  /**
   * Create a new character-stream writer whose critical sections will
   * synchronize on the writer itself.
   */
  public MemoryStringWriter(final int bufferSize) {
    this(bufferSize, bufferSize * 4);
  }

  public MemoryStringWriter(final int bufferSize, final int maximumBufferIncrement) {
    this.maximumBufferIncrement = maximumBufferIncrement;
    this.bufferIncrement = bufferSize;
    this.buffer = new char[bufferSize];
  }

  /**
   * Write a portion of an array of characters.
   * 
   * @param cbuf
   *          Array of characters
   * @param off
   *          Offset from which to start writing characters
   * @param len
   *          Number of characters to write
   * @throws java.io.IOException
   *           If an I/O error occurs
   */
  public synchronized void write(final char[] cbuf, final int off, final int len)
      throws IOException {
    if (len < 0) {
      throw new IllegalArgumentException();
    }
    if (off < 0) {
      throw new IndexOutOfBoundsException();
    }
    if (cbuf == null) {
      throw new NullPointerException();
    }
    if ((len + off) > cbuf.length) {
      throw new IndexOutOfBoundsException();
    }

    ensureSize(cursor + len);

    System.arraycopy(cbuf, off, this.buffer, cursor, len);
    cursor += len;
  }

  private void ensureSize(final int size) {
    if (this.buffer.length >= size) {
      return;
    }

    final int computedSize = (int) Math.min((this.buffer.length + 1) * 1.5, this.buffer.length
        + maximumBufferIncrement);
    final int newSize = Math.max(size, computedSize);
    final char[] newBuffer = new char[newSize];
    System.arraycopy(this.buffer, 0, newBuffer, 0, cursor);
    this.buffer = newBuffer;
  }

  /**
   * Flush the stream. If the stream has saved any characters from the various
   * write() methods in a buffer, write them immediately to their intended
   * destination. Then, if that destination is another character or byte stream,
   * flush it. Thus one flush() invocation will flush all the buffers in a chain
   * of Writers and OutputStreams. <p/> If the intended destination of this
   * stream is an abstraction provided by the underlying operating system, for
   * example a file, then flushing the stream guarantees only that bytes
   * previously written to the stream are passed to the operating system for
   * writing; it does not guarantee that they are actually written to a physical
   * device such as a disk drive.
   * 
   * @throws java.io.IOException
   *           If an I/O error occurs
   */
  public void flush() throws IOException {

  }

  /**
   * Close the stream, flushing it first. Once a stream has been closed, further
   * write() or flush() invocations will cause an IOException to be thrown.
   * Closing a previously-closed stream, however, has no effect.
   * 
   * @throws java.io.IOException
   *           If an I/O error occurs
   */
  public void close() throws IOException {
  }

  public int getCursor() {
    return cursor;
  }

  public String toString() {
    return new String(buffer, 0, cursor);
  }
}