如何使用Java逐行读取大文本文件? [英] How can I read a large text file line by line using Java?

问题描述

我需要使用Java逐行读取大约5-6 GB的大型文本文件.

I need to read a large text file of around 5-6 GB line by line using Java.

如何快速执行此操作?

推荐答案

一种常见的模式是使用

try (BufferedReader br = new BufferedReader(new FileReader(file))) {
    String line;
    while ((line = br.readLine()) != null) {
       // process the line.
    }
}

如果您假设没有字符编码，则可以更快地读取数据.例如ASCII-7，但差别不大.处理数据的时间很可能会花费更长的时间.

You can read the data faster if you assume there is no character encoding. e.g. ASCII-7 but it won't make much difference. It is highly likely that what you do with the data will take much longer.

一种不太常用的模式，可以避免line泄漏的范围.

A less common pattern to use which avoids the scope of line leaking.

try(BufferedReader br = new BufferedReader(new FileReader(file))) {
    for(String line; (line = br.readLine()) != null; ) {
        // process the line.
    }
    // line is not visible here.
}

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更新:在Java 8中，您可以做到

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UPDATE: In Java 8 you can do

try (Stream<String> stream = Files.lines(Paths.get(fileName))) {
        stream.forEach(System.out::println);
}

注意:您必须将Stream放在 try-with-资源块，以确保在其上调用#close方法，否则，直到GC以后再执行时，底层文件句柄才永远不会关闭.

NOTE: You have to place the Stream in a try-with-resource block to ensure the #close method is called on it, otherwise the underlying file handle is never closed until GC does it much later.

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