/**
 * 读文件大小
 */
public class ReadFileCallable implements Callable<Long> {

    private String fileName;

    public ReadFileCallable(String fileName) {
        this.fileName = fileName;
    }

    /**
     * 计算文件大小并返回
     */
    @Override
    public Long call() throws Exception {
        File f = new File(fileName);
        if (f.exists() && f.isFile()) {
            return f.length();
        } else {
            return null;
        }
    }

    /**
     * 测试
     */
    public static void main(String[] args) throws InterruptedException, ExecutionException {
        FutureTask<Long> task = new FutureTask<Long>(new ReadFileCallable("D:\\temp\\501.txt"));
        Thread thread = new Thread(task);
        thread.start();
        System.out.println(task.get());// 等待结果返回
    }
}