快速阅读文本文件的最后一行? [英] Quickly read the last line of a text file?

问题描述

在 Java 中从 [非常、非常大] 文件中读取最后一行文本的最快和最有效的方法是什么?

What's the quickest and most efficient way of reading the last line of text from a [very, very large] file in Java?

推荐答案

看看我对 C# 的类似问题.代码将非常相似，尽管 Java 中的编码支持有所不同.

Have a look at my answer to a similar question for C#. The code would be quite similar, although the encoding support is somewhat different in Java.

基本上，这不是一件非常容易的事情.正如 MSalter 指出的那样，UTF-8 确实可以很容易地识别 或 ，因为这些字符的 UTF-8 表示与 ASCII 相同，并且这些字节不会出现在多字节字符中.

Basically it's not a terribly easy thing to do in general. As MSalter points out, UTF-8 does make it easy to spot or as the UTF-8 representation of those characters is just the same as ASCII, and those bytes won't occur in multi-byte character.

所以基本上，取一个(比如)2K 的缓冲区，并逐渐向后读取(在之前跳到 2K，读取下一个 2K)检查行终止.然后跳到流中的正确位置，在顶部创建一个 InputStreamReader，并在其顶部创建一个 BufferedReader.然后只需调用 BufferedReader.readLine().

So basically, take a buffer of (say) 2K, and progressively read backwards (skip to 2K before you were before, read the next 2K) checking for a line termination. Then skip to exactly the right place in the stream, create an InputStreamReader on the top, and a BufferedReader on top of that. Then just call BufferedReader.readLine().

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