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Guava is a suite of core and expanded libraries that include utility classes, google's collections, io classes, and much much more.

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/*
 * Copyright (C) 2007 The Guava Authors
 *
 * Licensed 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 com.google.common.io;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.J2ktIncompatible;
import java.io.FilterOutputStream;
import java.io.IOException;
import java.io.OutputStream;

/**
 * An OutputStream that counts the number of bytes written.
 *
 * @author Chris Nokleberg
 * @since 1.0
 */
@J2ktIncompatible
@GwtIncompatible
@ElementTypesAreNonnullByDefault
public final class CountingOutputStream extends FilterOutputStream {

  private long count;

  /**
   * Wraps another output stream, counting the number of bytes written.
   *
   * @param out the output stream to be wrapped
   */
  public CountingOutputStream(OutputStream out) {
    super(checkNotNull(out));
  }

  /** Returns the number of bytes written. */
  public long getCount() {
    return count;
  }

  @Override
  public void write(byte[] b, int off, int len) throws IOException {
    out.write(b, off, len);
    count += len;
  }

  @Override
  public void write(int b) throws IOException {
    out.write(b);
    count++;
  }

  // Overriding close() because FilterOutputStream's close() method pre-JDK8 has bad behavior:
  // it silently ignores any exception thrown by flush(). Instead, just close the delegate stream.
  // It should flush itself if necessary.
  @Override
  public void close() throws IOException {
    out.close();
  }
}