[BUG][Java][Spring] Spring generator generates invalid class names that start with numbers

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

I downloaded the .jar on Windows and used it to generate a spring boot project. To my surprise, this project does not even compile (generation itself is successful). The reason is an edge case in the api definition: Some of the api urls start with a number (2faDevices, for example). The generated controller interface is then called 2faDevicesApiController, which is not a valid name for a class because it starts with a number. This should not be the default behaviour.

openapi-generator version

Version 6.2.1

Reproduction

I cannot provide concrete data to reproduce the issue, but anyone familiar with the tool should be able to easily reproduce it themselves.

Suggest a fix

There are two possible solutions:

• Prefix such names with a valid literal (like N2fa, "N" for number)
• write the name of the number out (like Twofa

No source file or test is named. Start with the Spring generator and an OpenAPI definition containing a path or operation name beginning with a digit, then inspect the generated controller interface name. Done means the generated Java project uses valid class names and compiles for such inputs.