Fix bug with rewrite password for user and refactor

src/main/java/com/Samsung/TaskTraker_Server/Repository/DataBase.java

@@ -119,7 +119,8 @@ public class DataBase {
         PreparedStatement getUser_stmt = connection.prepareStatement("SELECT * FROM user WHERE login = ?");
         getUser_stmt.setString(1, login);
         ResultSet resultSet = getUser_stmt.executeQuery();
-        resultSet.next();
+        if(!resultSet.next())
+            return null;
 
         int id = resultSet.getInt(1);
         String pass = resultSet.getNString(3);

src/main/java/com/Samsung/TaskTraker_Server/Repository/UserRepository.java

@@ -9,6 +9,8 @@ public class UserRepository {
 
     private final List<User> UserCache = new ArrayList<>();
 
+    private UserRepository() {}
+
     public static synchronized UserRepository getRepository() {
         if (instance == null) {
             instance = new UserRepository();
@@ -17,6 +19,16 @@ public class UserRepository {
     }
 
     public User AddUser(String login, String password) throws SQLException {
+        for (User i : UserCache) {
+            if(i.getLogin().equals(login)) {
+                return null;
+            }
+        }
+
+        User find = DataBase.getInstance().FindUser(login);
+        if(find != null)
+            return null;
+
         User user = new User(0, login, password);
 
         DataBase.getInstance().SaveUser(user);

src/main/java/com/Samsung/TaskTraker_Server/TaskTrakerServerApplication.java

@@ -67,10 +67,15 @@ public class TaskTrakerServerApplication {
     String SingUp(@RequestParam(name = "login", defaultValue = "null") String login, @RequestParam(name = "password", defaultValue = "null") String pass) {
         if (login.length() > 20 || pass.length() > 20)
             return "{\n\t\"status\":\"big\",\n\t\"token\":\"null\"\n}";
-        if (login.equals("null") || pass.equals("null"))
+        else if(login.isEmpty() || pass.isEmpty())
+            return "{\n\t\"status\":\"small\",\n\t\"token\":\"null\"\n}";
+        else if (login.equals("null") || pass.equals("null"))
             return "{\n\t\"status\":\"error\",\n\t\"token\":\"null\"\n}";
         try {
-            User token = UserRepository.getRepository().AddUser(login, pass);
+            User user = UserRepository.getRepository().AddUser(login, pass);
+            if(user == null)
+                return "{\n\t\"status\":\"error\"\n}";
+
             return "{\n\t\"status\":\"ok\"\n}";
         } catch (SQLException e) {
             return "{\n\t\"status\":\"error\"\n}";