org.apache.commons.io.output.ThresholdingOutputStream Maven / Gradle / Ivy
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/*
* 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.
*
* This class overrides all OutputStream methods. However, these
* overrides ultimately call the corresponding methods in the underlying output
* stream implementation.
*
* NOTE: This implementation may trigger the event before the threshold
* is actually reached, since it triggers when a pending write operation would
* cause the threshold to be exceeded.
*/
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.
*/
// True iff the thresholdReached() method has been called.
// Not used in the isThresholdExceeded() method.
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.
*
* @throws IOException if an error occurs.
*/
@Override
public void write(final int b) throws IOException
{
checkThreshold(1);
getStream().write(b);
written++;
}
/**
* Writes b.length bytes from the specified byte array to this
* output stream.
*
* @param b The array of bytes to be written.
*
* @throws IOException if an error occurs.
*/
@Override
public void write(final byte[] b) throws IOException
{
checkThreshold(b.length);
getStream().write(b);
written += b.length;
}
/**
* Writes len bytes from the specified byte array starting at
* offset off 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.
*
* @throws 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.
*
* @throws 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.
*
* @throws IOException if an error occurs.
*/
@Override
public void close() throws IOException
{
try
{
flush();
}
catch (final 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} if the threshold has been reached;
* {@code false} 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.
*
* @throws IOException if an error occurs.
*/
protected void checkThreshold(final 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;
}
/**
* Sets the byteCount to count. Useful for re-opening an output stream
* that has previously been written to.
*
* @param count The number of bytes that have already been written to the
* output stream
*
* @since 2.5
*/
protected void setByteCount(final long count) {
this.written = count;
}
// ------------------------------------------------------- Abstract methods
/**
* Returns the underlying output stream, to which the corresponding
* OutputStream methods in this class will ultimately delegate.
*
* @return The underlying output stream.
*
* @throws 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. Guaranteed to be called
* at most once.
*
* @throws IOException if an error occurs.
*/
protected abstract void thresholdReached() throws IOException;
}