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.IOException;
  import java.io.OutputStream;
  
  
  /**
   * An output stream which triggers an event when a specified number of bytes of
   * data have been written to it. The event can be used, for example, to throw
   * an exception if a maximum has been reached, or to switch the underlying
   * stream type when the threshold is exceeded.
   * <p>
   * This class overrides all <code>OutputStream</code> methods. However, these
   * overrides ultimately call the corresponding methods in the underlying output
   * stream implementation.
   * <p>
   * NOTE: This implementation may trigger the event <em>before</em> the threshold
   * is actually reached, since it triggers when a pending write operation would
   * cause the threshold to be exceeded.
   *
   * @author <a href="mailto:martinc@apache.org">Martin Cooper</a>
   *
   * @version $Id: ThresholdingOutputStream.java 736890 2009-01-23 02:02:22Z niallp $
   */
  public abstract class ThresholdingOutputStream
      extends OutputStream
  {
  
      // ----------------------------------------------------------- Data members
  
  
      /**
       * The threshold at which the event will be triggered.
       */
      private final int threshold;
  
  
      /**
       * The number of bytes written to the output stream.
       */
      private long written;
  
  
      /**
       * Whether or not the configured threshold has been exceeded.
       */
      private boolean thresholdExceeded;
  
  
      // ----------------------------------------------------------- Constructors
  
  
      /**
       * Constructs an instance of this class which will trigger an event at the
       * specified threshold.
       *
       * @param threshold The number of bytes at which to trigger an event.
       */
      public ThresholdingOutputStream(int threshold)
      {
          this.threshold = threshold;
      }
  
  
      // --------------------------------------------------- OutputStream methods
  
  
      /**
       * Writes the specified byte to this output stream.
       *
       * @param b The byte to be written.
       *
       * @exception IOException if an error occurs.
       */
      @Override
      public void write(int b) throws IOException
      {
          checkThreshold(1);
          getStream().write(b);
          written++;
      }
  
  
      /**
       * Writes <code>b.length</code> bytes from the specified byte array to this
       * output stream.
       *
       * @param b The array of bytes to be written.
       *
       * @exception IOException if an error occurs.
       */
      @Override
      public void write(byte b[]) throws IOException
      {
          checkThreshold(b.length);
          getStream().write(b);
          written += b.length;
      }
  
  
      /**
       * Writes <code>len</code> bytes from the specified byte array starting at
       * offset <code>off</code> to this output stream.
       *
       * @param b   The byte array from which the data will be written.
       * @param off The start offset in the byte array.
       * @param len The number of bytes to write.
       *
       * @exception IOException if an error occurs.
       */
      @Override
      public void write(byte b[], int off, int len) throws IOException
      {
          checkThreshold(len);
          getStream().write(b, off, len);
          written += len;
      }
  
  
      /**
       * Flushes this output stream and forces any buffered output bytes to be
       * written out.
       *
       * @exception IOException if an error occurs.
       */
      @Override
      public void flush() throws IOException
      {
          getStream().flush();
      }
  
  
      /**
       * Closes this output stream and releases any system resources associated
       * with this stream.
       *
       * @exception IOException if an error occurs.
       */
      @Override
      public void close() throws IOException
      {
          try
          {
              flush();
          }
          catch (IOException ignored)
          {
              // ignore
          }
          getStream().close();
      }
  
  
      // --------------------------------------------------------- Public methods
  
  
      /**
       * Returns the threshold, in bytes, at which an event will be triggered.
       *
       * @return The threshold point, in bytes.
       */
      public int getThreshold()
      {
          return threshold;
      }
  
  
      /**
       * Returns the number of bytes that have been written to this output stream.
       *
       * @return The number of bytes written.
       */
      public long getByteCount()
      {
          return written;
      }
  
  
      /**
       * Determines whether or not the configured threshold has been exceeded for
       * this output stream.
       *
       * @return <code>true</code> if the threshold has been reached;
       *         <code>false</code> otherwise.
       */
      public boolean isThresholdExceeded()
      {
          return (written > threshold);
      }
  
  
      // ------------------------------------------------------ Protected methods
  
  
      /**
       * Checks to see if writing the specified number of bytes would cause the
       * configured threshold to be exceeded. If so, triggers an event to allow
       * a concrete implementation to take action on this.
       *
       * @param count The number of bytes about to be written to the underlying
       *              output stream.
       *
       * @exception IOException if an error occurs.
       */
      protected void checkThreshold(int count) throws IOException
      {
          if (!thresholdExceeded && (written + count > threshold))
          {
              thresholdExceeded = true;
              thresholdReached();
          }
      }
  
      /**
       * Resets the byteCount to zero.  You can call this from 
       * {@link #thresholdReached()} if you want the event to be triggered again. 
       */
      protected void resetByteCount() 
      {
          this.thresholdExceeded = false;
          this.written = 0;
      }
  
      // ------------------------------------------------------- Abstract methods
  
  
      /**
       * Returns the underlying output stream, to which the corresponding
       * <code>OutputStream</code> methods in this class will ultimately delegate.
       *
       * @return The underlying output stream.
       *
       * @exception IOException if an error occurs.
       */
      protected abstract OutputStream getStream() throws IOException;
  
  
      /**
       * Indicates that the configured threshold has been reached, and that a
       * subclass should take whatever action necessary on this event. This may
       * include changing the underlying output stream.
       *
       * @exception IOException if an error occurs.
       */
      protected abstract void thresholdReached() throws IOException;
  }
  