Ignoring Specific Patterns Between Delimiters When Comparing Text Files in Core Java

Question

I'm working with two text files, File1.txt and File2.txt, and comparing them using Core Java. While doing so, I need to disregard certain values in the comparison.

Specifically, any value that falls between the strings XYZ and ZYX should be excluded from the comparison.

Here's a brief example of the contents of the two files:

File1.txt

-----------------------------
XYZ12345ZYX
abcddd......
I am going to Delhi .............
Mumbai isgoodXYZ6789ZYX

File2.txt

----------------------------
XYZ111111ZYX
abcddd......
I am going to Delhi .............
Mumbai isgoodXYZ00000ZYX

From the example:

• The values 12345 in File1.txt and 111111 in File2.txt should be ignored.
• The values 6789 in File1.txt and 00000 in File2.txt should also be ignored.

I'm curious to know if anyone is familiar with a widely-recognized method, algorithm, or logic to address this challenge. Any experiences or suggestions?

Answer 1

The solution below uses the java.nio.file and java.util.regex packages. It reads the files line by line and utilizes a regex pattern to identify and replace the specific patterns ("XYZ...ZYX") with a constant placeholder ("XYZIGNOREZYX").

import java.io.*;
import java.nio.file.*;
import java.util.stream.*;
import java.util.regex.*;

public class FileComparison {
    public static void main(String[] args) throws IOException {
        Path file1Path = Paths.get("File1.txt");
        Path file2Path = Paths.get("File2.txt");

        // Use process method below to remove random text 
        // between your static bounded text 
        List<String> file1Lines = processFile(file1Path);
        List<String> file2Lines = processFile(file2Path);

        // Now you can compare file1Lines and file2Lines

    }

    // This method will identify pattern and replace the random text
    // identified by regex with a constant value
    private static List<String> processFile(Path filePath) throws IOException {
        Pattern pattern = Pattern.compile("XYZ.*?ZYX");
        return Files.lines(filePath)
            .map(line -> {
                Matcher matcher = pattern.matcher(line);
                return matcher.replaceAll("XYZIGNOREZYX");
            })
            .collect(Collectors.toList());
    }
}

The regex pattern .*? matches any number of any characters, but as few as possible to still make the match (this is called non-greedy matching - use this link to learn more).

This is necessary to correctly handle lines that contain multiple "XYZ...ZYX" patterns.

The replaceAll method replaces all matches of the regex with "XYZIGNOREZYX"