FutureTest.java

package future;

import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.concurrent.FutureTask;

/**
 * @author Cay Horstmann
 * @version 1.01 2012-01-26
 */
public class FutureTest {
    public static void main(String[] args) {
        try (Scanner in = new Scanner(System.in)) {
            System.out.print("Enter base directory (e.g. /usr/local/jdk5.0/src): ");
            String directory = in.nextLine();
            System.out.print("Enter keyword (e.g. volatile): ");
            String keyword = in.nextLine();

            MatchCounter counter = new MatchCounter(new File(directory), keyword);
            FutureTask<Integer> task = new FutureTask<>(counter);
            Thread t = new Thread(task);
            t.start();
            try {
                System.out.println(task.get() + " matching files.");
            } catch (ExecutionException e) {
                e.printStackTrace();
            } catch (InterruptedException ignored) {
            }
        }
    }
}

/**
 * This task counts the files in a directory and its subdirectories that contain a given keyword.
 */
class MatchCounter implements Callable<Integer> {
    private File directory;
    private String keyword;

    /**
     * Constructs a MatchCounter.
     *
     * @param directory the directory in which to start the search
     * @param keyword   the keyword to look for
     */
    public MatchCounter(File directory, String keyword) {
        this.directory = directory;
        this.keyword = keyword;
    }

    public Integer call() {
        int count = 0;
        try {
            File[] files = directory.listFiles();
            List<Future<Integer>> results = new ArrayList<>();

            assert files != null;
            for (File file : files)
                if (file.isDirectory()) {
                    MatchCounter counter = new MatchCounter(file, keyword);
                    FutureTask<Integer> task = new FutureTask<>(counter);
                    results.add(task);
                    Thread t = new Thread(task);
                    t.start();
                } else {
                    if (search(file)) count++;
                }

            for (Future<Integer> result : results)
                try {
                    count += result.get();
                } catch (ExecutionException e) {
                    e.printStackTrace();
                }
        } catch (InterruptedException ignored) {
        }
        return count;
    }

    /**
     * Searches a file for a given keyword.
     *
     * @param file the file to search
     * @return true if the keyword is contained in the file
     */
    public boolean search(File file) {
        try {
            try (Scanner in = new Scanner(file, "UTF-8")) {
                boolean found = false;
                while (!found && in.hasNextLine()) {
                    String line = in.nextLine();
                    if (line.contains(keyword)) found = true;
                }
                return found;
            }
        } catch (IOException e) {
            return false;
        }
    }
}