CountBytes.java

/*
 * Copyright 2016 Google Inc. All Rights Reserved.
 *
 * 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.cloud.examples.nio;

import com.google.common.base.Stopwatch;
import com.google.common.io.BaseEncoding;

import java.io.IOException;
import java.net.URI;
import java.nio.ByteBuffer;
import java.nio.channels.SeekableByteChannel;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.security.MessageDigest;
import java.util.concurrent.TimeUnit;

/**
 * CountBytes will read through the whole file given as input.
 *
 * <p>This example shows how to read a file size using NIO.
 * File.size returns the size of the file as saved in Storage metadata.
 * This class also shows how to read all of the file's contents using NIO,
 * computes a MD5 hash, and reports how long it took.
 *
 * <p>See the
 * <a href="https://github.com/GoogleCloudPlatform/gcloud-java/blob/master/gcloud-java-examples/README.md">
 * README</a> for compilation instructions. Run this code with
 * <pre>{@code target/appassembler/bin/CountBytes <file>}</pre>
 */
public class CountBytes {

  /**
   * See the class documentation.
   */
  public static void main(String[] args) throws IOException {
    if (args.length == 0 || args[0].equals("--help")) {
      help();
      return;
    }
    for (String a : args) {
      countFile(a);
    }
  }

  /**
   * Print the length of the indicated file.
   *
   * <p>This uses the normal Java NIO Api, so it can take advantage of any installed
   * NIO Filesystem provider without any extra effort.
   */
  private static void countFile(String fname) {
    // large buffers pay off
    final int bufSize = 50 * 1024 * 1024;
    try {
      Path path = Paths.get(new URI(fname));
      long size = Files.size(path);
      System.out.println(fname + ": " + size + " bytes.");
      ByteBuffer buf = ByteBuffer.allocate(bufSize);
      System.out.println("Reading the whole file...");
      Stopwatch sw = Stopwatch.createStarted();
      try (SeekableByteChannel chan = Files.newByteChannel(path)) {
        long total = 0;
        int readCalls = 0;
        MessageDigest md = MessageDigest.getInstance("MD5");
        while (chan.read(buf) > 0) {
          readCalls++;
          md.update(buf.array(), 0, buf.position());
          total += buf.position();
          buf.flip();
        }
        readCalls++; // We must count the last call
        long elapsed = sw.elapsed(TimeUnit.SECONDS);
        System.out.println("Read all " + total + " bytes in " + elapsed + "s. " +
            "(" + readCalls +" calls to chan.read)");
        String hex = String.valueOf(BaseEncoding.base16().encode(md.digest()));
        System.out.println("The MD5 is: 0x" + hex);
        if (total != size) {
          System.out.println("Wait, this doesn't match! We saw " + total + " bytes, " +
              "yet the file size is listed at " + size + " bytes.");
        }
      }
    } catch (Exception ex) {
      System.out.println(fname + ": " + ex.toString());
    }
  }

  private static void help() {
    String[] help =
        {"The argument is a <path>",
         "and we show the length of that file."
        };
    for (String s : help) {
      System.out.println(s);
    }
  }
}