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Commons IO example source code file (ThresholdingOutputStream.java)

This example Commons IO source code file (ThresholdingOutputStream.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Commons IO tags/keywords

io, ioexception, ioexception, outputstream, outputstream, override, override, thresholdingoutputstream, thresholdingoutputstream

The Commons IO ThresholdingOutputStream.java source 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 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 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
 *
 * @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 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 bytes from the specified byte array starting at
     * offset <code>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.
     *
     * @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 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.
     *
     * @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 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;
}

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