A line counter utility, written in Java, to demonstrate the new NIO file API.

LineCounter.java

/*
 * Copyright (C) 2010 Graham Edgecombe.
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.FileChannel.MapMode;
import java.nio.file.FileVisitResult;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.SimpleFileVisitor;
import java.nio.file.StandardOpenOption;
import java.nio.file.attribute.BasicFileAttributes;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.regex.Pattern;

/**
 * A utility for counting the number of lines in a file.
 * @author Graham Edgecombe
 */
public final class LineCounter extends SimpleFileVisitor<Path> {

	/**
	 * The entry point of the application.
	 * @param args The command line arguments.
	 */
	public static void main(String[] args) {
		if (args.length != 2) {
			System.err.println("Usage:");
			System.err.println("  " + LineCounter.class.getName() + " [path] [pattern]");
			System.err.println();
			System.err.println("Where [path] is the relative or absolute path and [pattern] is the regex pattern for matching countable files.");
			return;
		}
				
		Pattern pattern = Pattern.compile(args[1]);
		
		AtomicInteger fileCounter = new AtomicInteger();
		AtomicInteger lineCounter = new AtomicInteger();
		
		Path path = Paths.get(args[0]).normalize();
		Files.walkFileTree(path, new LineCounter(pattern, fileCounter, lineCounter));
		
		System.out.println(lineCounter.get() + " lines in " + fileCounter.get() + " files");
		System.out.println("  in " + path + " and subdirectories");
		System.out.println("  matching the pattern " + pattern);
	}
	
	/**
	 * The file name pattern.
	 */
	private final Pattern pattern;
	
	/**
	 * The file counter.
	 */
	private final AtomicInteger fileCounter;
	
	/**
	 * The line counter.
	 */
	private final AtomicInteger lineCounter;
	
	/**
	 * Creates the line counter.
	 * @param pattern The pattern.
	 * @param fileCounter The file counter.
	 * @param lineCounter The line counter.
	 */
	public LineCounter(Pattern pattern, AtomicInteger fileCounter, AtomicInteger lineCounter) {
		this.pattern = pattern;
		this.fileCounter = fileCounter;
		this.lineCounter = lineCounter;
	}

	/*
	 * (non-Javadoc)
	 * @see java.nio.file.SimpleFileVisitor#visitFile(java.lang.Object, java.nio.file.attribute.BasicFileAttributes)
	 */
	@Override
	public FileVisitResult visitFile(Path path, BasicFileAttributes attributes) {
		try {
			if (pattern.matcher(path.toString()).find()) {
				fileCounter.incrementAndGet();
				FileChannel channel = FileChannel.open(path, StandardOpenOption.READ);
				ByteBuffer buffer;
				try {
					buffer = channel.map(MapMode.READ_ONLY, 0, channel.size());
				} finally {
					channel.close();
				}
				int lines = 0;
				for (int i = 0; i < buffer.remaining(); i++) {
					byte b = buffer.get();
					if (b == '\n') {
						lines++;
					}
				}
				lineCounter.addAndGet(lines);
			}
			return FileVisitResult.CONTINUE;
		} catch (IOException ex) {
			return FileVisitResult.TERMINATE;
		}
	}

}