    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.io.output;
    018
    019import java.io.IOException;
    020import java.io.OutputStream;
    021
    022import org.apache.commons.io.function.IOConsumer;
    023import org.apache.commons.io.function.IOFunction;
    024
    025/**
    026 * An output stream which triggers an event when a specified number of bytes of data have been written to it. The event
    027 * can be used, for example, to throw an exception if a maximum has been reached, or to switch the underlying stream
    028 * type when the threshold is exceeded.
    029 * <p>
    030 * This class overrides all {@link OutputStream} methods. However, these overrides ultimately call the corresponding
    031 * methods in the underlying output stream implementation.
    032 * </p>
    033 * <p>
    034 * NOTE: This implementation may trigger the event <em>before</em> the threshold is actually reached, since it triggers
    035 * when a pending write operation would cause the threshold to be exceeded.
    036 * </p>
    037 */
    038public class ThresholdingOutputStream extends OutputStream {
    039
    040    /**
    041     * Noop output stream getter function.
    042     */
    043    private static final IOFunction<ThresholdingOutputStream, OutputStream> NOOP_OS_GETTER = os -> NullOutputStream.INSTANCE;
    044
    045    /**
    046     * The threshold at which the event will be triggered.
    047     */
    048    private final int threshold;
    049
    050    /**
    051     * Accepts reaching the threshold.
    052     */
    053    private final IOConsumer<ThresholdingOutputStream> thresholdConsumer;
    054
    055    /**
    056     * Gets the output stream.
    057     */
    058    private final IOFunction<ThresholdingOutputStream, OutputStream> outputStreamGetter;
    059
    060    /**
    061     * The number of bytes written to the output stream.
    062     */
    063    private long written;
    064
    065    /**
    066     * Whether or not the configured threshold has been exceeded.
    067     */
    068    private boolean thresholdExceeded;
    069
    070    /**
    071     * Constructs an instance of this class which will trigger an event at the specified threshold.
    072     *
    073     * @param threshold The number of bytes at which to trigger an event.
    074     */
    075    public ThresholdingOutputStream(final int threshold) {
    076        this(threshold, IOConsumer.noop(), NOOP_OS_GETTER);
    077    }
    078
    079    /**
    080     * Constructs an instance of this class which will trigger an event at the specified threshold.
    081     *
    082     * @param threshold The number of bytes at which to trigger an event.
    083     * @param thresholdConsumer Accepts reaching the threshold.
    084     * @param outputStreamGetter Gets the output stream.
    085     * @since 2.9.0
    086     */
    087    public ThresholdingOutputStream(final int threshold, final IOConsumer<ThresholdingOutputStream> thresholdConsumer,
    088        final IOFunction<ThresholdingOutputStream, OutputStream> outputStreamGetter) {
    089        this.threshold = threshold;
    090        this.thresholdConsumer = thresholdConsumer == null ? IOConsumer.noop() : thresholdConsumer;
    091        this.outputStreamGetter = outputStreamGetter == null ? NOOP_OS_GETTER : outputStreamGetter;
    092    }
    093
    094    /**
    095     * Checks to see if writing the specified number of bytes would cause the configured threshold to be exceeded. If
    096     * so, triggers an event to allow a concrete implementation to take action on this.
    097     *
    098     * @param count The number of bytes about to be written to the underlying output stream.
    099     *
    100     * @throws IOException if an error occurs.
    101     */
    102    protected void checkThreshold(final int count) throws IOException {
    103        if (!thresholdExceeded && written + count > threshold) {
    104            thresholdExceeded = true;
    105            thresholdReached();
    106        }
    107    }
    108
    109    /**
    110     * Closes this output stream and releases any system resources associated with this stream.
    111     *
    112     * @throws IOException if an error occurs.
    113     */
    114    @Override
    115    public void close() throws IOException {
    116        try {
    117            flush();
    118        } catch (final IOException ignored) {
    119            // ignore
    120        }
    121        getStream().close();
    122    }
    123
    124    /**
    125     * Flushes this output stream and forces any buffered output bytes to be written out.
    126     *
    127     * @throws IOException if an error occurs.
    128     */
    129    @SuppressWarnings("resource") // the underlying stream is managed by a subclass.
    130    @Override
    131    public void flush() throws IOException {
    132        getStream().flush();
    133    }
    134
    135    /**
    136     * Returns the number of bytes that have been written to this output stream.
    137     *
    138     * @return The number of bytes written.
    139     */
    140    public long getByteCount() {
    141        return written;
    142    }
    143
    144    /**
    145     * Returns the underlying output stream, to which the corresponding {@link OutputStream} methods in this class will
    146     * ultimately delegate.
    147     *
    148     * @return The underlying output stream.
    149     *
    150     * @throws IOException if an error occurs.
    151     */
    152    protected OutputStream getStream() throws IOException {
    153        return outputStreamGetter.apply(this);
    154    }
    155
    156    /**
    157     * Returns the threshold, in bytes, at which an event will be triggered.
    158     *
    159     * @return The threshold point, in bytes.
    160     */
    161    public int getThreshold() {
    162        return threshold;
    163    }
    164
    165    /**
    166     * Determines whether or not the configured threshold has been exceeded for this output stream.
    167     *
    168     * @return {@code true} if the threshold has been reached; {@code false} otherwise.
    169     */
    170    public boolean isThresholdExceeded() {
    171        return written > threshold;
    172    }
    173
    174    /**
    175     * Resets the byteCount to zero. You can call this from {@link #thresholdReached()} if you want the event to be
    176     * triggered again.
    177     */
    178    protected void resetByteCount() {
    179        this.thresholdExceeded = false;
    180        this.written = 0;
    181    }
    182
    183    /**
    184     * Sets the byteCount to count. Useful for re-opening an output stream that has previously been written to.
    185     *
    186     * @param count The number of bytes that have already been written to the output stream
    187     *
    188     * @since 2.5
    189     */
    190    protected void setByteCount(final long count) {
    191        this.written = count;
    192    }
    193
    194    /**
    195     * Indicates that the configured threshold has been reached, and that a subclass should take whatever action
    196     * necessary on this event. This may include changing the underlying output stream.
    197     *
    198     * @throws IOException if an error occurs.
    199     */
    200    protected void thresholdReached() throws IOException {
    201        thresholdConsumer.accept(this);
    202    }
    203
    204    /**
    205     * Writes {@code b.length} bytes from the specified byte array to this output stream.
    206     *
    207     * @param b The array of bytes to be written.
    208     *
    209     * @throws IOException if an error occurs.
    210     */
    211    @SuppressWarnings("resource") // the underlying stream is managed by a subclass.
    212    @Override
    213    public void write(final byte[] b) throws IOException {
    214        checkThreshold(b.length);
    215        getStream().write(b);
    216        written += b.length;
    217    }
    218
    219    /**
    220     * Writes {@code len} bytes from the specified byte array starting at offset {@code off} to this output stream.
    221     *
    222     * @param b The byte array from which the data will be written.
    223     * @param off The start offset in the byte array.
    224     * @param len The number of bytes to write.
    225     *
    226     * @throws IOException if an error occurs.
    227     */
    228    @SuppressWarnings("resource") // the underlying stream is managed by a subclass.
    229    @Override
    230    public void write(final byte[] b, final int off, final int len) throws IOException {
    231        checkThreshold(len);
    232        getStream().write(b, off, len);
    233        written += len;
    234    }
    235
    236    /**
    237     * Writes the specified byte to this output stream.
    238     *
    239     * @param b The byte to be written.
    240     *
    241     * @throws IOException if an error occurs.
    242     */
    243    @SuppressWarnings("resource") // the underlying stream is managed by a subclass.
    244    @Override
    245    public void write(final int b) throws IOException {
    246        checkThreshold(1);
    247        getStream().write(b);
    248        written++;
    249    }
    250}