如何处理PHP开发中的文件上传和下载问题

<form action="upload.php" method="post" enctype="multipart/form-data">
    <input type="file" name="file">
    <input type="submit" value="上传">
</form>

<?php
if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    $file = $_FILES['file'];

    // 获取文件名
    $filename = $file['name'];

    // 获取文件的临时路径
    $tmpPath = $file['tmp_name'];

    // 处理文件上传操作，如将文件移动到指定目录
    $targetPath = 'uploads/' . $filename;
    move_uploaded_file($tmpPath, $targetPath);

    echo "文件上传成功！";
}
?>

<a href="download.php?filename=file.txt">下载文件</a>

<?php
if ($_SERVER['REQUEST_METHOD'] === 'GET') {
    $filename = $_GET['filename'];
    $filePath = 'uploads/' . $filename;

    if (file_exists($filePath)) {
        header('Content-Description: File Transfer');
        header('Content-Type: application/octet-stream');
        header('Content-Disposition: attachment; filename=' . basename($filePath));
        header('Content-Transfer-Encoding: binary');
        header('Expires: 0');
        header('Cache-Control: must-revalidate');
        header('Pragma: public');
        header('Content-Length: ' . filesize($filePath));

        readfile($filePath);
        exit;
    } else {
        echo "文件不存在！";
    }
}
?>