What's the difference between using a Service compared to using a repository? Spring Boot

Here is two examples.

Example 1:

Create a CRUD database with Entity, Repository and then Service.
https://github.com/alejandro-du/crudui/tree/master/demo/src/main/java/org/vaadin/crudui/demo

And the use of the code can be shown here:
https://github.com/alejandro-du/crudui/blob/master/demo/src/main/java/org/vaadin/crudui/demo/ui/view/SimpleCrudView.java

Here we can see that UserService userService and GroupService groupService are being used for storing values in the CRUD database.

Example 2:

Here is an example by me where I'm using @Autowired Repository

https://github.com/DanielMartensson/OpenSourceLogger/tree/master/src/main/java/se/danielmartensson/views

Here: https://github.com/DanielMartensson/OpenSourceLogger/blob/master/src/main/java/se/danielmartensson/views/MySQLView.java

Question:

What is the difference between using a Service Object rather than using @Autowired Repository

Example:

If I using @Autowired Repository backend here, I can write to the CRUD database here.

    crud.setCrudListener(new CrudListener<User>() {
@Override
public Collection<User> findAll() {
return backend.findAllUsers();
}
@Override
public User add(User user) {
return backend.add(user);
}
@Override
public User update(User user) {
return backend.update(user);
}
@Override
public void delete(User user) {
backend.remove(user);
}
});

And if I'm using Service object like this one. I can also write to the CRUD database.

@Route(value = "simple", layout = MainLayout.class)
public class SimpleCrudView extends VerticalLayout {
public SimpleCrudView(UserService userService, GroupService groupService) {
// crud instance
GridCrud<User> crud = new GridCrud<>(User.class);
// grid configuration
crud.getGrid().setColumns("name", "birthDate", "maritalStatus", "email", "phoneNumber", "active");
crud.getGrid().setColumnReorderingAllowed(true);
// form configuration
crud.getCrudFormFactory().setUseBeanValidation(true);
crud.getCrudFormFactory().setVisibleProperties(
"name", "birthDate", "email", "salary", "phoneNumber", "maritalStatus", "groups", "active", "mainGroup");
crud.getCrudFormFactory().setVisibleProperties(
CrudOperation.ADD,
"name", "birthDate", "email", "salary", "phoneNumber", "maritalStatus", "groups", "active", "mainGroup",
"password");
crud.getCrudFormFactory().setFieldProvider("mainGroup",
new ComboBoxProvider<>(groupService.findAll()));
crud.getCrudFormFactory().setFieldProvider("groups",
new CheckBoxGroupProvider<>(groupService.findAll()));
crud.getCrudFormFactory().setFieldProvider("groups",
new CheckBoxGroupProvider<>("Groups", groupService.findAll(), Group::getName));
crud.getCrudFormFactory().setFieldProvider("mainGroup",
new ComboBoxProvider<>("Main Group", groupService.findAll(), new TextRenderer<>(Group::getName), Group::getName));
// layout configuration
setSizeFull();
add(crud);
crud.setFindAllOperationVisible(false);
// logic configuration
crud.setOperations(
() -> userService.findAll(),
user -> userService.save(user),
user -> userService.save(user),
user -> userService.delete(user)
);
}
}

IMO, when you work on the service layer, you can inject multi repository, but if you using repository so there's only 1 entity object.

basically just CRUD on 1 entity object, service does not take much advantage. but when you working from 2 entities which have some connection in business logic then service makes more sense.