Update client server

GoGreen/Server/src/main/java/gogreen/server/service/UserService.java

@@ -0,0 +1,40 @@
+package gogreen.server.service;
+
+import gogreen.common.ApplicationException;
+import gogreen.common.UserDTO;
+import gogreen.server.data.model.User;
+import gogreen.server.data.repository.UserRepository;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.stereotype.Service;
+
+@Service
+public class UserService {
+    Logger logger = LoggerFactory.getLogger(UserService.class);
+    @Autowired
+    UserRepository userRepository;
+
+    public UserDTO registerUser(String name, String password) {
+        User user = userRepository.findByName(name);
+        if (user != null) {
+            throw new ApplicationException("User already exists");
+        } else {
+            user = userRepository.save(new User(null, name, password));
+        }
+        logger.info("Created user id=" + user.getId() + ", name=" + user.getName());
+        return new UserDTO(user.getId(), user.getName());
+    }
+
+    public UserDTO login(String name, String password) {
+        User user = userRepository.findByName(name);
+        if (user == null) {
+            throw new ApplicationException("User does not exist");
+        } else {
+            if (!user.getPassword().equals(password)) {
+                throw new ApplicationException("Wrong password");
+            }
+        }
+        return new UserDTO(user.getId(), user.getName());
+    }
+}