How to Efficiently Retrieve the Last Line (or Lines) of a Large Text File in Java?

Efficiently Retrieve the Last Line of a Large Text File in Java

When dealing with extremely large text files, finding the most efficient way to extract the last line becomes imperative. This article delves into two methods that provide the quickest solutions in Java.

Method 1: Retrieving the Last Non-Blank Line

The 'tail' function offered here excels in retrieving the last non-blank line without stepping through or loading the entire file. It skillfully navigates to the last character and iterates backward until encountering a line break. This approach not only saves time but also preserves the original file content.

public String tail( File file ) {
    ...
}

Method 2: Retrieving the Last N Lines

For scenarios where obtaining the last N lines is necessary, the 'tail2' function proves effective. It follows a similar logic to 'tail,' but it keeps track of the line count to accurately retrieve the desired number of lines.

public String tail2( File file, int lines) {
    ...
}

Invocation Example:

To utilize these methods, instantiate a File object and pass it as an argument to either 'tail' or 'tail2.'

File file = new File("D:\stuff\huge.log");
System.out.println(tail(file));
System.out.println(tail2(file, 10));

Note on Unicode Reversal:

It's essential to acknowledge a potential issue with unicode characters during the reversal process. Certain characters with accents, diacritics, or special symbols may not be rendered correctly when the string is reversed. Thorough testing is recommended for diverse language scenarios.

For further insights into this phenomenon, refer to the provided URL:

https://codeblog.jonskeet.uk/2009/11/02/omg-ponies-aka-humanity-epic-fail/

By implementing these efficient methods, developers can confidently retrieve the last line or multiple lines from even the largest text files in Java.

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