Can't use method findOne() in Spring boot

Your UserRepository is defined as CrudRepository<User,String>. Where User is the type and String the type of the id. However your User class has an id field of the type int NOT of type String.

First fix your UserRepository to be a proper representation of your User.

public interface UserRepository extends CrudRepository<User, Integer> {}

Next create a method to find your User by name.

public User findByName(String name);

And call this from your controller instead of findOne. The findOne is used to find entities based on ID not on any random field of your entity.