How to remove Java OutOfMemoryError

I have a program which gets a very big txt data and changes the order of some columns in this txt data. For more details about what it does exactly see my question here. I use a list with maps and I can imagine that this is too much for the java virtual machine since the txt file has 400,000 entries but I have no idea what do else. I have tried it with a smaller txt file and then it works fine. Otherwise it runs for more than an hour and then I get an OutOfMemoryError.

Here is my code:

import java.io.BufferedReader;
import java.io.File;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.TreeMap;

public class Final {

public static void main(String[] args) {

    String path = "C:\\\\\\\\Users\\\\\\\\Ferid\\\\\\\\Downloads\\\\\\\\secdef\\\\\\\\secdef.txt";

    File file = new File(path);

    new Final().updateFile(file);
}

private void updateFile(File file) {

    List<String> allRows = getAllRows(file);

    String[] baseRow = allRows.get(0).split("\\|");

    List<String> columns = getBaseColumns(baseRow);
    System.out.println(columns.size());

    appendNewColumns(allRows, columns);
    System.out.println(columns.size());

    List<Map<String, String>> mapList = convertToMap(allRows, columns);

    List<String> newList = new ArrayList<String>();

    appendHeader(columns, newList);

    appendData(mapList, newList, columns);

    String toPath = "C:\\\\\\\\Users\\\\\\\\Ferid\\\\\\\\Downloads\\\\\\\\secdef\\\\\\\\finalz2.txt";

    writeToNewFile(newList, toPath);

}

/**
 * Gibt alle Zeilen aus der Datei zurück.
 */
private static List<String> getAllRows(File file) {

    List<String> allRows = new ArrayList<>();
    BufferedReader reader = null;
    try {
        reader = new BufferedReader(new FileReader(file));
        String row = null;
        int i = 0;
        while ((row = reader.readLine()) != null) {
            allRows.add(row);

        }
    } catch (IOException e) {
        e.printStackTrace();
    }
    return allRows;
}

/**
 * Gibt die Hauptspalten aus der 1. Zeile zurück.
 */
private static List<String> getBaseColumns(String[] baseRow) {
    List<String> columns = new ArrayList<>();
    for (String rowEntry : baseRow) {
        String[] entry = rowEntry.split("=");
        columns.add(entry[0]);
    }
    return columns;
}

/**
 * Fügt alle neuen Spalten hinzu.
 */
private static void appendNewColumns(List<String> rows, List<String> columns) {
    for (String row : rows) {
        String[] splittedRow = row.split("\\|");
        for (String column : splittedRow) {
            String[] entry = column.split("=");
            if (columns.contains(entry[0])) {
                continue;
            }
            columns.add(entry[0]);
        }
    }
}

/**
 * Konvertiert die Listeneinträge zu Maps.
 */
private static List<Map<String, String>> convertToMap(List<String> rows, List<String> columns) {
    List<Map<String, String>> mapList = new ArrayList<>();
    for (String row : rows) {
        Map<String, String> map = new TreeMap<>();
        String[] splittedRow = row.split("\\|");
        List<String> rowList = Arrays.asList(splittedRow);
        for (String col : columns) {
            String newCol = findByColumn(rowList, col);
            if (newCol == null) {
                map.put(col, "null");
            } else {
                String[] arr = newCol.split("=");
                map.put(col, arr[1]);
            }
        }
        mapList.add(map);
    }
    return mapList;

}

/**
 * 
 */
private static String findByColumn(List<String> row, String col) {
    return row.stream().filter(o -> o.startsWith(col)).findFirst().orElse(null);
}

/**
 * Fügt die Header-Zeile in die neue Liste hinzu.
 */
private static void appendHeader(List<String> columns, List<String> list1) {
    String header = "";
    for (String column : columns) {
        header += column + "|";
    }
    list1.add(header + "\n");
}

/**
 * Fügt alle Daten in die entsprechenden neuen Dateien hinzu.
 */
private static void appendData(List<Map<String, String>> mapList, List<String> list1, List<String> columns) {
    for (Map<String, String> entry : mapList) {
        String line = "";
        for (String key : columns) {
            // for (String key : entry.keySet()) {
            line += entry.get(key) + "|";
        }

        list1.add(line + "\n");
    }
}

/**
 * Schreibt alle Werte in die neue Datei.
 */
private static void writeToNewFile(List<String> list, String path) {
    FileOutputStream out = null;
    try {
        out = new FileOutputStream(new File(path));
        for (String line : list) {
            out.write(line.getBytes());
        }
        out.close();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

}