[BUG][Java][Spring] Incorrect code generation with regular expressions

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Description

Using the java Spring generator, string regex patterns have forward slashes somehow additionally escaped, changing the meaning of the pattern.

openapi-generator version

Versions 4.3.1 and 5.0.0

OpenAPI declaration file content or URL

openapi: 3.0.2
...
components:
  parameters:
    ClientKey:
      name: clientKey
      in: header
      description: "Client key"
      schema:
        type: string
        pattern: '^(?!\s*$).+'
...

Generation Details

Generated line:

default ResponseEntity<Void> deleteTokens(@Pattern(regexp="^(?!\\s*$).+") @ApiParam(value = "User token")   String userToken) {
        return new ResponseEntity<>(HttpStatus.NOT_IMPLEMENTED);
    }

Expected line:

default ResponseEntity<Void> deleteTokens(@Pattern(regexp="^(?!\s*$).+") @ApiParam(value = "User token")   String userToken) {
        return new ResponseEntity<>(HttpStatus.NOT_IMPLEMENTED);
    }

As you can see, the pattern (@Pattern(regexp="^(?!\\s*$).+") ) has one slash too many and modifies the regex.