Added getting sorted students

buisnesslogic/src/main/java/com/plannaplan/services/UserService.java

@@ -3,6 +3,7 @@ package com.plannaplan.services;
 import java.util.List;
 import java.util.Optional;
 import java.util.UUID;
+import java.util.stream.Collectors;
 
 import com.plannaplan.entities.User;
 import com.plannaplan.exceptions.UserNotFoundException;
@@ -153,4 +154,15 @@ public class UserService {
         return this.repo.getAllByRole(UserRoles.ADMIN).size() > 0;
     }
 
+    /**
+     * get students sorted by their ranking
+     * 
+     * @return list of students
+     */
+    public List<User> getStudentsSortedByRanking() {
+        return this.repo.getAllByRole(UserRoles.STUDENT).stream().sorted((u1, u2) -> {
+            return -1 * u1.getRanking().compareTo(u2.getRanking());
+        }).collect(Collectors.toList());
+    }
+
 }