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Apache Commons VFS is a Virtual File System library.
There is a newer version: 2.9.0
/*
 * 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.vfs2.util;

import java.io.BufferedInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicLong;

/**
 * An InputStream that provides buffering and end-of-stream monitoring.
 */
public class MonitorInputStream extends BufferedInputStream {
    private static final int EOF_CHAR = -1;
    private final AtomicBoolean finished = new AtomicBoolean(false);
    private final AtomicLong atomicCount = new AtomicLong(0);

    public MonitorInputStream(final InputStream in) {
        super(in);
    }

    /**
     * Returns 0 if the stream is at EOF, else the underlying inputStream will be queried.
     *
     * @return The number of bytes that are available.
     * @throws IOException if an error occurs.
     * @since 2.0
     */
    @Override
    public synchronized int available() throws IOException {
        if (finished.get()) {
            return 0;
        }

        return super.available();
    }

    /**
     * Reads a character.
     *
     * @return The character that was read as an integer.
     * @throws IOException if an error occurs.
     */
    @Override
    public int read() throws IOException {
        if (finished.get()) {
            return EOF_CHAR;
        }

        final int ch = super.read();
        if (ch != EOF_CHAR) {
            atomicCount.incrementAndGet();
            return ch;
        }

        // End-of-stream
        close();
        return EOF_CHAR;
    }

    /**
     * Reads bytes from this input stream.
     *
     * @param buffer A byte array in which to place the characters read.
     * @param offset The offset at which to start reading.
     * @param length The maximum number of bytes to read.
     * @return The number of bytes read.
     * @throws IOException if an error occurs.
     */
    @Override
    public int read(final byte[] buffer, final int offset, final int length) throws IOException {
        if (finished.get()) {
            return EOF_CHAR;
        }

        final int nread = super.read(buffer, offset, length);
        if (nread != EOF_CHAR) {
            atomicCount.addAndGet(nread);
            return nread;
        }

        // End-of-stream
        close();
        return EOF_CHAR;
    }

    /**
     * Closes this input stream and releases any system resources associated with the stream.
     *
     * @throws IOException if an error occurs.
     */
    @Override
    public void close() throws IOException {
        final boolean closed = finished.getAndSet(true);
        if (closed) {
            return;
        }

        // Close the stream
        IOException exc = null;
        try {
            super.close();
        } catch (final IOException ioe) {
            exc = ioe;
        }

        // Notify that the stream has been closed
        try {
            onClose();
        } catch (final IOException ioe) {
            exc = ioe;
        }

        if (exc != null) {
            throw exc;
        }
    }

    /**
     * Called after the stream has been closed. This implementation does nothing.
     *
     * @throws IOException if an error occurs.
     */
    protected void onClose() throws IOException {
    }

    /**
     * Get the number of bytes read by this input stream.
     *
     * @return The number of bytes read by this input stream.
     */
    public long getCount() {
        return atomicCount.get();
    }
}