You installed a framework Spring for a simple feature to grab some text from a POST request and dump it into a database.
Since in general you don't have thousands of users sending feedback at the same time I don't need a framework and if you know how to correctly create SQL statements you don't need a framework for SQL. There is nothing to log, if the db call fails you can put some text in a log file or do a curl to a different url to notify you.
It will also be probably faster then a Java framework since you don't have a function call stack 30 levels deep (not a Java issue , all magic frameworks including PHP one have such giant call stacks)
It depends on the customer, will they give you a server dedicated for your Java framework so you can handle at maximum 5 POST request per day or will day give you access to the existing website they have for the company, that already has PHP,mysql installed. Honestly you are not doing the fair thing for the customer if you ask for a new server because you want to use your prefered tool and not the best thing for this job.
Btw my scenario was about sending feedback ro stack traces, this are just text, no giant file uploads and nothing insecure about it.
And it will likely be an order of magnitude more scalable & reliable than the PHP, having proper logging, security features, etc.
Whereas such PHP systems in my experience tend to be unreliable, in need of maintenance and often broken.
The Java/ Spring Boot option will also take you all the way to a high-end commercial system/ large website/ webapp.