什么时候FileInputStream.read()阻止?

本文介绍了什么时候FileInputStream.read()阻止?的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

问题类似于以下两个问题.

The question is similar to the following two questions.

• Java InputStream阻止读取
• 为什么FileInputStream read()没有被阻止?

• Java InputStream blocking read
• Why is the FileInputStream read() not blocking?

但是我仍然不能完全理解它.

But I still cannot fully understand it.

到目前为止，由于空文件"test.txt"，我认为以下代码中的 read()方法将被阻止.

So far I think the read() method in following code will block due to the empty file 'test.txt'.

FileInputStream fis = new FileInputStream("c:/test.txt"); System.out.println(fis.read()); System.out.println("to the end");

实际上它会打印-1，我想知道为什么.

Actually it will print -1, I want to know why.

Javadoc说如果尚无可用输入，则此方法会阻塞.

The javadoc says This method blocks if no input is yet available.

"无可用输入"是什么意思?

谢谢.

推荐答案

您的问题的答案可以在用于.read()的JavaDoc :

The answer to your question can be found in the JavaDoc for .read():

如果没有可用的输入，此方法将阻塞.

This method blocks if no input is yet available.

和

返回:下一个数据字节；如果到达文件末尾，则返回-1.

Returns: the next byte of data, or -1 if the end of the file is reached.

因此，一个空文件将立即为您提供-1(而不是read()阻止)

So, an empty file will get you an immediate -1 (instead of read() blocking) as

• 有 个输入可用，因为该文件存在
• ...但是它是空的，所以立即生效.

• there is input available, since the file exists
• ...but it is empty, so immediate EOF.

...尚无输入... 情况可能会发生，例如当一个是从一个命名管道而不是一个普通文件读取时，而管道的另一端还没有写任何东西.

The ...No input is yet available... situation could occur eg. when one was to read from a named pipe instead of a plain file, and the other side of the pipe hasn't written anything yet.

干杯