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* Copyright 2001-2004 The Apache Software Foundation.
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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* http://www.apache.org/licenses/LICENSE-2.0
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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package org.apache.commons.io.output;
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import java.io.IOException;
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import java.io.OutputStream;
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* An output stream which triggers an event when a specified number of bytes of
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* data have been written to it. The event can be used, for example, to throw
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* an exception if a maximum has been reached, or to switch the underlying
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* stream type when the threshold is exceeded.
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* This class overrides all <code>OutputStream</code> methods. However, these
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* overrides ultimately call the corresponding methods in the underlying output
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* stream implementation.
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* NOTE: This implementation may trigger the event <em>before</em> the threshold
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* is actually reached, since it triggers when a pending write operation would
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* cause the threshold to be exceeded.
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* @author <a href="mailto:martinc@apache.org">Martin Cooper</a>
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* @version $Id: ThresholdingOutputStream.java,v 1.2 2004/02/23 04:40:29 bayard Exp $
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public abstract class ThresholdingOutputStream
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// ----------------------------------------------------------- Data members
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* The threshold at which the event will be triggered.
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private int threshold;
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* The number of bytes written to the output stream.
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* Whether or not the configured threshold has been exceeded.
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private boolean thresholdExceeded;
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// ----------------------------------------------------------- Constructors
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* Constructs an instance of this class which will trigger an event at the
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* specified threshold.
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* @param threshold The number of bytes at which to trigger an event.
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public ThresholdingOutputStream(int threshold)
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this.threshold = threshold;
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// --------------------------------------------------- OutputStream methods
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* Writes the specified byte to this output stream.
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* @param b The byte to be written.
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* @exception IOException if an error occurs.
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public void write(int b) throws IOException
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* Writes <code>b.length</code> bytes from the specified byte array to this
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* @param b The array of bytes to be written.
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* @exception IOException if an error occurs.
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public void write(byte b[]) throws IOException
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checkThreshold(b.length);
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getStream().write(b);
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* Writes <code>len</code> bytes from the specified byte array starting at
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* offset <code>off</code> to this output stream.
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* @param b The byte array from which the data will be written.
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* @param off The start offset in the byte array.
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* @param len The number of bytes to write.
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* @exception IOException if an error occurs.
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public void write(byte b[], int off, int len) throws IOException
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getStream().write(b, off, len);
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* Flushes this output stream and forces any buffered output bytes to be
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* @exception IOException if an error occurs.
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public void flush() throws IOException
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* Closes this output stream and releases any system resources associated
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* @exception IOException if an error occurs.
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public void close() throws IOException
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catch (IOException ignored)
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// --------------------------------------------------------- Public methods
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* Returns the threshold, in bytes, at which an event will be triggered.
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* @return The threshold point, in bytes.
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public int getThreshold()
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* Returns the number of bytes that have been written to this output stream.
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* @return The number of bytes written.
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public long getByteCount()
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* Determines whether or not the configured threshold has been exceeded for
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* this output stream.
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* @return <code>true</code> if the threshold has been reached;
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* <code>false</code> otherwise.
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public boolean isThresholdExceeded()
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return (written > threshold);
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// ------------------------------------------------------ Protected methods
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* Checks to see if writing the specified number of bytes would cause the
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* configured threshold to be exceeded. If so, triggers an event to allow
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* a concrete implementation to take action on this.
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* @param count The number of bytes about to be written to the underlying
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* @exception IOException if an error occurs.
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protected void checkThreshold(int count) throws IOException
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if (!thresholdExceeded && (written + count > threshold))
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thresholdExceeded = true;
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// ------------------------------------------------------- Abstract methods
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* Returns the underlying output stream, to which the corresponding
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* <code>OutputStream</code> methods in this class will ultimately delegate.
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* @return The underlying output stream.
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* @exception IOException if an error occurs.
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protected abstract OutputStream getStream() throws IOException;
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* Indicates that the configured threshold has been reached, and that a
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* subclass should take whatever action necessary on this event. This may
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* include changing the underlying output stream.
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* @exception IOException if an error occurs.
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protected abstract void thresholdReached() throws IOException;
added
removed
src/java/org/apache/commons/io/output/ThresholdingOutputStream.java
