如何使回声发挥作用。在浏览器上打印输出并下载csv？

Question

我有这段代码，

<?php
  require "vendor/autoload.php";
  error_reporting(E_ALL);

  use \Objects\Csv as Csv;

  $csv = new Csv();

  $originalCsv = $csv->getCsv('OriginalInventory.csv');
  $updpateCsv  = $csv->getCsv('UpdatedInventory.csv');
  $finalCsv    = $csv->mergeCsv($originalCsv, $updpateCsv);

  echo "Duplicate Style #s: " . $csv->duplicate;
  echo "<br>";
  echo "Items missing from Original CSV: " . $csv->missing;

  $csv->download();

和这种下载方法

  public function download()
  {
    # Download
    header("Content-Type:application/csv");
    header("Content-Disposition:merge;filename=FullInventory-merged.csv");

    $output = fopen("php://output",'w') or die("Can't open php://output");
    fputcsv($output, $this->new[0]);
    unset($this->new[0]);

    foreach ($this->new as $key => $value) {
      fputcsv($output, $value);
    }

    fclose($output) or die("Can't close php://output");

  }

如何使回声发挥作用。在浏览器上打印输出并下载csv？

鉴于我的代码，这只会下载csv但不会在浏览器上显示打印。