I thought the driver was not loaded before, so I added it

Class.forName("com.mysql.cj.jdbc.Driver");

After discovering the error, I read the error code again: no suitable driver found for localhost: 3306/upload_file

It turned out that the URL was misspelled and not prefixed: jdbc:mysql://

Attach the complete URL, and remember to add the suffix parameter

jdbc:mysql://localhost:3306/upload_file?&useSSL=false&serverTimezone=UTC