The app expects a MySQL database at localhost:3306/temperatures (This can be changed in application.properties). There should be a table called temperature with the following definition:

CREATE TABLE `temperature` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `value` float NOT NULL,
  `create_date` datetime NOT NULL,
  `update_date` datetime DEFAULT NULL,
  PRIMARY KEY (`id`)
)

Run gradlew bootRun and the app should start up after downloading any dependencies.

Go to localhost:8080 in a browser for a (very minimal) UI that can interact with the REST API. You can use the browser dev tools to inspect the HTTP requests.