When docker creates an image, the error is not a valid repository/tag

docker build -t study-javaExercise-web .

invalid argument "study-javaExercise-web" for t: Error parsing reference: "study-javaExercise-web" is not a valid repository/tag

See 'docker build --help'.

I thought that the name of study-javaExercise-web was too long, and it was created successfully after shortening it.

After several attempts, the real reason is that there is an uppercase E in the name, and the uppercase is changed to lowercase, and the creation is successful.

Pit, there is no requirement in the document that it can only be lowercase.