/**
 * 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
  }
}