How can I split a CSV file into different CSV files by line in Java?

If you're on Linux and you can run the CSV through a script first, then you can use "split":

$ split -l 100000 big.csv small-

This generates files named small-aa, small-ab, small-ac... To rename these to csv's if needed:

$ for a in small-*; do 
    mv $a $a.csv;                # rename split files to .csv 
    java MyCSVProcessor $a.csv;  # or just process them anyways 
done

Try this for additional options:

$ split -h

-a –suffix-length=N use suffixes of length N (default 2)
-b –bytes=SIZE put SIZE bytes per output file
-C –line-bytes=SIZE put at most SIZE bytes of lines per output file
-d –numeric-suffixes use numeric suffixes instead of alphabetic
-l –lines=NUMBER put NUMBER lines per output file

This is however a poor mitigation for your problem - the reason your CSV reader module is running out of memory, is because it's either reading the whole file into memory before splitting it, or it's doing that and keeping your processed output in memory. To make your code more portable and universally runnable, you should consider processing one line at a time - and splitting the input yourself, line by line. (From https://stackabuse.com/reading-and-writing-csvs-in-java/)

BufferedReader csvReader = new BufferedReader(new FileReader(pathToCsv));
while ((row = csvReader.readLine()) != null) {
    String[] data = row.split(",");
    // do something with the data
}
csvReader.close();

Caveat with the above code is that quoted commas will just be treated as new columns - you will have to add some additional processing if your CSV data contains quoted commas.

Of course, if you really want to use your existing code, and just want to split the file, you can adapt the above:

import java.io.*;

public class split {

    static String CSVFile="test.csv";
    static String row;
    static BufferedReader csvReader;
    static PrintWriter csvWriter;

    public static void main(String[] args) throws IOException {   

    csvReader = new BufferedReader(new FileReader(CSVFile));

    int line = 0;
    while ((row = csvReader.readLine()) != null) {
       if (line % 100000 == 0) {  // maximum lines per file
          if (line>0) { csvWriter.close(); }
          csvWriter = new PrintWriter("cut-"+Integer.toString(line)+CSVFile);
       }
       csvWriter.println(row);
        // String[] data = row.split(",");
        // do something with the data
       line++;
    }
    csvWriter.close();
    csvReader.close();

    }
}

I chose PrintWriter above FileWriter or BufferedWriter because it automatically prints the relevent newlines - and I would presume that it's buffered... I've not written anything in Java in 20 years, so I bet you can improve on the above.

I created a simple fun to create a childcsv from parent based on the start and last Range. It can be used as splitter based on line range.

public static void createcsv(String csvPath,String newcsvPath, int startRange, int lastRange) {
    csvPath = csvPath.trim();
    String childcsvPath = newcsvPath.trim();
    Scanner sc = null;
    FileWriter writer = null;
    int count = 0;
    // Iterate to startRange Location
    try {
        sc = new Scanner(new File(csvPath));
        sc.useDelimiter(","); // sets the delimiter pattern
        ArrayList<String> newCsv = new ArrayList<String>();

        while (sc.hasNextLine()) // returns a boolean value
        {
            String value = sc.nextLine();
            count++;
            if (count > lastRange)
                break;

            else if (count >= startRange) {
                newCsv.add(value);
            } else
                continue;
        }

        writer = new FileWriter(childcsvPath);

        for (int j = 0; j < newCsv.size(); j++) {
            writer.append(newCsv.get(j));
            writer.append("\n");
        }
    } catch (Exception e) {
        System.out.print("Exception Found" + e);
    } finally {
        if (sc != null) {
            try {
                sc.close();
                writer.close();
            } catch (Exception e) {
            }
        }
    }
}