ExecutorService的submit方法的坑

    public Future<?> submit(Runnable task) {
        if (task == null) throw new NullPointerException();
        RunnableFuture<Void> ftask = newTaskFor(task, null);
        execute(ftask);
        return ftask;
    }

 protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) {
        return new FutureTask<T>(runnable, value);
    }

 ListenableFutureTask<RecordSet> f = new SecondTaskFutureTask(new Callable<RecordSet>() {
            @Override
            public RecordSet call() throws Exception {
                RecordSet rs = process.process(pw);
                return rs;
            }
        });
        ex.execute(f);
        RecordSet rs = f.get();