implement registration validity checks

src/main/java/wtf/beatrice/releasehive/services/UserServiceImpl.java

@@ -0,0 +1,34 @@
+package wtf.beatrice.releasehive.services;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.security.core.userdetails.UsernameNotFoundException;
+import org.springframework.stereotype.Service;
+import wtf.beatrice.releasehive.models.User;
+import wtf.beatrice.releasehive.repositories.UserRepository;
+
+import java.util.List;
+
+@Service
+public class UserServiceImpl implements UserService
+{
+    private final UserRepository userRepository;
+
+    public UserServiceImpl(@Autowired UserRepository userRepository) {
+        this.userRepository = userRepository;
+    }
+
+    @Override
+    public List<User> getAllUsers() {
+        return userRepository.findAll();
+    }
+
+    @Override
+    public User loadUserByUsername(String username) throws UsernameNotFoundException {
+        return userRepository.findByUsername(username).orElseThrow(() -> new UsernameNotFoundException(username));
+    }
+
+    @Override
+    public User loadUserByEmail(String email) throws UsernameNotFoundException {
+        return userRepository.findByEmail(email).orElseThrow(() -> new UsernameNotFoundException(email));
+    }
+}