java cat with buffered IO

package dburyak.sandbox;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.time.Duration;
import java.time.Instant;
import java.util.Scanner;

public class CatBuffered {
    public static void main(String[] args) {
        var numPreHeatIterationsStr = System.getenv("X_PREHEAT_ITERATIONS");
        if (numPreHeatIterationsStr == null) {
            numPreHeatIterationsStr = "500";
        }
        var inputBufferSizeStr = System.getenv("X_INPUT_BUFFER_SIZE");
        if (inputBufferSizeStr == null) {
            inputBufferSizeStr = "8192";
        }
        var outputBufferSizeStr = System.getenv("X_OUTPUT_BUFFER_SIZE");
        if (outputBufferSizeStr == null) {
            outputBufferSizeStr = "8192";
        }

        var numPreheatIterations = Integer.parseInt(numPreHeatIterationsStr);
        var inputBufferSize = Integer.parseInt(inputBufferSizeStr);
        var outputBufferSize = Integer.parseInt(outputBufferSizeStr);
        var filePath = args[0];

        try (var out = new BufferedWriter(new OutputStreamWriter(System.out), outputBufferSize)) {
            out.append("preheating .....").flush();
            var preheatingStartedAt = Instant.now();
            for (int i = 0; i < numPreheatIterations; i++) {
                printFileWithReadline(filePath, inputBufferSize, out);
            }
            var preheatingTime = Duration.between(preheatingStartedAt, Instant.now());
            out.flush();

            var startedAt = Instant.now();
            printFileWithReadline(filePath, inputBufferSize, out);
            out.flush();
            var catTime = Duration.between(startedAt, Instant.now());

            out.append("num preheat operations : ").append(numPreHeatIterationsStr);
            out.newLine();
            out.append("preheat time : ").append(preheatingTime.toString());
            out.newLine();
            out.append("input buffer size : ").append(inputBufferSizeStr);
            out.newLine();
            out.append("output buffer size : ").append(outputBufferSizeStr);
            out.newLine();
            out.append("cat time : ").append(catTime.toString());
            out.newLine();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private static void printFileWithReadline(String filePath, int inputBufferSize, BufferedWriter out) {
        try (var input = new BufferedReader(new FileReader(filePath), inputBufferSize)) {
            String line = null;
            while ((line = input.readLine()) != null) {
                out.append(line);
                out.newLine();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private static void printFileWithScanner(String filePath, int inputBufferSize, BufferedWriter out) {
        try (var input = new BufferedReader(new FileReader(filePath), inputBufferSize)) {
            var scanner = new Scanner(input);
            while (scanner.hasNextLine()) {
                var line = scanner.nextLine();
                out.append(line);
                out.newLine();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}