Added get goal endpoint and logic

src/main/java/no/ntnu/idi/stud/savingsapp/controller/goal/GoalController.java

@@ -125,4 +125,11 @@ public class GoalController {
     challengeService.updateSavingAmount(identity.getId(), request.getId(), request.getAmount());
     return ResponseEntity.status(HttpStatus.ACCEPTED).build();
   }
+
+  @GetMapping(value = "/{id}", produces = MediaType.APPLICATION_JSON_VALUE)
+  public ResponseEntity<GoalDTO> getGoal(@RequestParam Long id) {
+    Goal goal = goalService.getGoal(id);
+    GoalDTO goalDTO = modelMapper.map(goal, GoalDTO.class);
+    return ResponseEntity.ok(goalDTO);
+  }
 }

src/main/java/no/ntnu/idi/stud/savingsapp/service/GoalService.java

@@ -31,4 +31,6 @@ public interface GoalService {
    *         The list may be empty if the user has no goals.
    */
   List<Goal> getGoals(long userId);
+
+  Goal getGoal(long goalId);
 }

src/main/java/no/ntnu/idi/stud/savingsapp/service/impl/GoalServiceImpl.java

@@ -3,7 +3,10 @@ package no.ntnu.idi.stud.savingsapp.service.impl;
 import java.sql.Timestamp;
 import java.time.Instant;
 import java.util.List;
+import java.util.Optional;
 
+import no.ntnu.idi.stud.savingsapp.exception.goal.ChallengeNotFoundException;
+import no.ntnu.idi.stud.savingsapp.exception.goal.GoalNotFoundException;
 import no.ntnu.idi.stud.savingsapp.model.goal.Challenge;
 import no.ntnu.idi.stud.savingsapp.model.goal.Goal;
 import no.ntnu.idi.stud.savingsapp.model.user.User;
@@ -56,4 +59,14 @@ public class GoalServiceImpl implements GoalService {
   public List<Goal> getGoals(long userId) {
     return goalRepository.findByUser_Id(userId);
   }
+
+  @Override
+  public Goal getGoal(long goalId) {
+    Optional<Goal> optionalGoal = goalRepository.findById(goalId);
+    if (optionalGoal.isPresent()) {
+      return optionalGoal.get();
+    } else {
+      throw new GoalNotFoundException();
+    }
+  }
 }