如何使用Java逐行读取大型文本文件？ [英] How to 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的大文本文件。

我该如何快速执行此操作？

解决方案

常见模式是使用

  try（BufferedReader br = new BufferedReader（new FileReader（file）））{
 String line; （（line = br.readLine（））！= null）{
 //处理行。 
 
 
 
 
 
 
你可以更快地读取数据，没有字符编码。例如ASCII-7，但不会有太大的区别。编辑：不常用的模式，避免使用的范围， 
 
 $ b 
  try（BufferedReader br = new BufferedReader（new FileReader（file）））{ 
 for（String line;（line = br.readLine（））！= null;）{
 //处理该行。 
} 
 //在这里不可见。 
 
 
 
 
 
 $ p $更新：在Java 8中你可以这样做：
 
 $ $ p $  try（Stream< String> stream = Files.lines（Paths.get（fileName）））{
 stream.forEach（System.out :: println）; 
 
 $ / code> 
注意：您必须将Stream放在try-with-resource块以确保调用#close方法，否则基本的文件句柄将永远不会关闭，直到GC晚了很久。
 
I need to read a large text file of around 5-6 GB line by line using Java.

How can I do this quickly? 
解决方案
A common pattern is to use
try (BufferedReader br = new BufferedReader(new FileReader(file))) {
    String line;
    while ((line = br.readLine()) != null) {
       // process the line.
    }
}
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.

EDIT: 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.
}




UPDATE: In Java 8 you can do
try (Stream<String> stream = Files.lines(Paths.get(fileName))) {
        stream.forEach(System.out::println);
}
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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