How to Efficiently Read the Last Line of a Large Text File in Java?

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

When working with massive text files, it becomes essential to handle file operations efficiently. One such task is retrieving the last line of the file without having to read the entire file. This article explores the most effective way to accomplish this in Java.

Tail Function for Last Line Retrieval

The tail function is a highly efficient approach for reading the last line of a file. It utilizes the RandomAccessFile class to access the file's content in random order, allowing us to quickly jump to the last character. We then step backward, character by character, until we encounter a newline character. This process continues until we reach the beginning of the file, capturing the collected characters in a string. By reversing this string, we obtain the last non-blank line of the file without loading or traversing the entire file.

Tail2 Function for Last N Lines

If you need to retrieve the last N lines instead of just the last line, you can utilize the tail2 function. This function follows a similar approach as tail but also keeps track of line count as we step backward through the file. Once it encounters N newline characters, it breaks out of the loop and returns the collected characters.

Implementation

Here's an example implementation of these functions:

public String tail(File file) {
    // ... Implementation of the tail function
}

public String tail2(File file, int lines) {
    // ... Implementation of the tail2 function
}

Usage

You can invoke the functions as follows:

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

Caution

It's important to note that this method may not handle non-Latin characters or emojis correctly due to unicode complications. For such cases, it's recommended to thoroughly test the code with the languages you intend to use it with.

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