目的

计算制定目录下所有大小总和.

代码

• 目录大小计算接口定义

public interface DirSizeCalc {
    long getSize(final File file);
}

• 多线程计算方式
  文件多时,执行优于递归

/**
 * 采用ForkJoinPool多线程计算目录大小
 */
public class DirSizeCalcByForkJoinPool implements DirSizeCalc {

    @Override
    public long getSize(final File file) {
        ForkJoinPool forkJoinPool = new ForkJoinPool();
        return forkJoinPool.invoke(new FileSizeFinder(file));
    }

    private static class FileSizeFinder extends RecursiveTask<Long> {
        final File file;

        FileSizeFinder(final File theFile) {
            file = theFile;
        }

        @Override
        public Long compute() {
            long size = 0;
            if (file.isFile()) {
                size = file.length();
            } else {
                final File[] children = file.listFiles();
                if (children != null) {
                    List<ForkJoinTask<Long>> tasks = new ArrayList<ForkJoinTask<Long>>();
                    for (final File child : children) {
                        if (child.isFile()) {
                            size += child.length();
                        } else {
                            tasks.add(new FileSizeFinder(child));
                        }
                    }
                    for (final ForkJoinTask<Long> task : invokeAll(tasks)) {
                        size += task.join();
                    }
                }
            }
            return size;
        }
    }
}

• 递归计算方式

/**
 * 采用递归调用计算目录大小
 */
public class DirSizeCalcByRecursion implements DirSizeCalc {
    @Override
    public long getSize(final File file) {
        if (file.isFile())
            return file.length();
        final File[] children = file.listFiles();
        long total = 0;
        if (children != null)
            for (final File child : children)
                total += getSize(child);
        return total;
    }
}

• 调用方法:

public class Test {
    public static void main(final String[] args) {
        String dirPath = "/users/jerry/projects/tms/tms";
        File file = new File(dirPath);

        System.out.print("递归方式计算\t");
        calcDirSize(file, new DirSizeCalcByRecursion());
        System.out.print("多线程方式计算\t");
        calcDirSize(file, new DirSizeCalcByForkJoinPool());
    }

    private static void calcDirSize(File file, DirSizeCalc dirSizeCalc) {
        long start = System.nanoTime();
        long total = dirSizeCalc.getSize(file);
        long end = System.nanoTime();
        System.out.println("目录大小: " + total+"；耗时: " + (end - start) / 1.0e9);
    }
}

• 执行结果样例:

递归方式计算	目录大小: 167502662；耗时: 0.233380609
多线程方式计算	目录大小: 167502662；耗时: 0.060410266