500 Error when testing monlog package - php

Question

I'm trying to test out the monolog package using composer (full disclosure: this is my first try using composer) and am getting a 500 error when running this code:
<?php
// composer autoloader
require_once 'vendor/autoload.php';
// Shortcuts for simpler usage
use \Monolog\Logger;
use \Monolog\Formatter\LineFormatter;
use \Monolog\Handler\StreamHandler;
// Common logger
$log = new Logger('files');
// Line formatter without empty brackets in the end
$formatter = new LineFormatter(null, null, false, true);
// Debug level handler
$debugHandler = new StreamHandler('debug.log', Logger::DEBUG);
$debugHandler->setFormatter($formatter);
// Error level handler
$errorHandler = new StreamHandler('error.log', Logger::ERROR);
$errorHandler->setFormatter($formatter);
// This will have both DEBUG and ERROR messages
$log->pushHandler($debugHandler);
// This will have only ERROR messages
$log->pushHandler($errorHandler);
// The actual logging
$log->debug('I am debug');
$log->error('I am error', array('productId' => 123));
?>
I see in Dreamweaver that the three 'use' lines in monolog_test.php are highlighted in red:
The error message is:
In my /Applications/MAMP/logs/php_error.log:
[03-Mar-2018 14:10:05 America/Toronto] PHP Fatal error: Class
'Monolog\Logger' not found in
/Users/Ross/Dropbox/htdocs/wonderfest/secure/contest/monolog_test.php
on line 13
My file system setup looks like this:
I installed Composer globally on my Mac and I know the installation is good because I was able to add some packages using composer require . My composer.json file:
{
"require": {
"monolog/monolog": "1.0",
"phpfastcache/phpfastcache": "^6.1",
"mpdf/mpdf": "^7.0"
}
}
And my vendor\autoload.php:
<?php
// autoload.php #generated by Composer
require_once __DIR__ . '/composer/autoload_real.php';
return ComposerAutoloaderInit348f040c8a2a7d48c0a311fb1af10c08::getLoader();
I guess my question is this: do I have to do anything other than install packages to make their namespaces available?

Answer 1

I updated monolog to the latest stable version and although the 3 'use' lines in Dreamweaver still show up as errors, it works. What threw me was this line on the monolog package page:
Monolog works with PHP 7.0 or above, use Monolog ^1.0 for PHP 5.3+ support.
I thought that meant that I needed to use v1.0 for my PHP 5.6.32, but when I removed that version constraint from the require command everything seems to work - I get the two logs in the same folder as the monolog_test.php file.
My new composer.json (with one additional packages installed):
{
"require": {
"monolog/monolog": "^1.23",
"mpdf/mpdf": "^7.0",
"phpfastcache/phpfastcache": "^6.1",
"phpmailer/phpmailer": "^6.0"
}
}