Скачать или смотреть How to Ignore \u000D End-of-Line Delimiters in Java's Files.lines

Learn how to ignore the `\u000D` (CARRIAGE RETURN) end-of-line delimiters in Java's Files.lines() method to process file streams efficiently.
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Ignoring \u000D End-of-Line Delimiters in Java's Files.lines Method

When working with file input in Java, especially when using Files.lines(), you may run into issues with how end-of-line (EOL) delimiters are treated. Specifically, you might find that your files contain \u000D (CARRIAGE RETURN) characters that you want to ignore as new line markers, which is different from how many tools, like grep, handle such characters. In this post, we'll explore how to handle this issue effectively while still processing your file as a stream in Java 8.

The Problem

Java's Files.lines() method reads lines from a file and uses the following delimiters to determine where one line ends and another begins:

\u000D\u000A (CARRIAGE RETURN followed by LINE FEED)

\u000A (LINE FEED)

\u000D (CARRIAGE RETURN)

When you have files that contain standalone \u000D characters, they can interfere with the way that Java processes lines, especially if you're trying to align your line counting with the output from grep. In this case, the present CARRIAGE RETURN character should not signify a new line, which can lead to inconsistencies between returned line numbers in an output from grep and your Java line processing.

The Solution

To address this problem, we can read the file on a byte-wise basis, avoiding the \u000D character being treated as a new line. Here's how you can implement this strategy:

A Byte-wise Input Approach

Here’s a scalable and efficient solution that avoids holding the entire file in memory or creating unnecessary string objects for each line that you skip:

[[See Video to Reveal this Text or Code Snippet]]

Explanation of the Code

File and Input Stream: Begin by creating an InputStream wrapped in a BufferedInputStream to handle file operations more efficiently.

Line Counter: Initialize a line counter to track the number of lines you've read, along with a variable for the line you want to access (wantedLine).

Reading Loop: Use a while loop that continues until you've read the desired line. Within this, a nested loop reads the bytes one-by-one until it encounters a new line or reaches the end of the file.

New Line Handling: Increment the line counter when a new line character (\n) is found.

Important Notes

Illustrative Nature: This code is primarily for demonstration purposes and may need refinement for production use.

Performance Considerations: You could enhance performance with a ByteBuffer, although this increases code complexity.

BufferedReader Alternative: Similar logic can be applied using BufferedReader, providing an additional layer of ease if you prefer that approach.

Resource Management: Always ensure you wrap your input streams in a try-with-resources statement to handle resource management properly and avoid memory leaks.

Conclusion

By employing a byte-wise input strategy, you can easily ignore unwanted \u000D characters while effectively processing file streams in Java. This method allows you to maintain consistency with external tools like grep, ensuring that you'll align output and file manipulations correctly.

Keep in mind to adapt the provided sample code based on your specific needs and always test in your environment to verify the correct handling of end-of-line delimiters.