/*
* 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.wicket.util.io;
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 $Id$
*/
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(final 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(final 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(final 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(final byte b[], final int off, final 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(final int count) throws IOException
{
if (!thresholdExceeded && (written + count > threshold))
{
thresholdReached();
thresholdExceeded = true;
}
}
// ------------------------------------------------------- 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;
}