chore: Refactor CategoryController to improve code structure and error handling

src/main/java/de/uni_passau/fim/PADAS/group3/DataDash/controler/CategoryController.java

@@ -3,12 +3,15 @@ import java.util.List;
 import java.util.UUID;
 
 import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.ResponseStatus;
 import org.springframework.web.bind.annotation.RestController;
 
 import de.uni_passau.fim.PADAS.group3.DataDash.model.CategoryDto;
 import de.uni_passau.fim.PADAS.group3.DataDash.model.CategoryService;
 
 import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
 import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.PathVariable;
 import org.springframework.web.bind.annotation.PostMapping;
@@ -29,14 +32,17 @@ public class CategoryController {
     }
 
     @GetMapping("/id/{id}")
-    public CategoryDto getMethodName(@PathVariable("id") UUID id) {
-        return categoryService.getCategoryById(id);
+    public ResponseEntity<?> fetchCategoryById(@PathVariable("id") UUID id) {
+        CategoryDto category = categoryService.getCategoryById(id);
+        if(category == null) {
+            return new ResponseEntity<>(HttpStatus.NOT_FOUND);
+        }
+        return new ResponseEntity<>(category, HttpStatus.OK);
     }
-
+    @ResponseStatus(HttpStatus.CREATED)
     @PostMapping
-    public String postMethodName(@RequestBody CategoryDto dto) {
+    public void createCategory(@RequestBody CategoryDto dto) {
         categoryService.addCategory(dto);        
-        return null;
     }
     
     

src/main/java/de/uni_passau/fim/PADAS/group3/DataDash/model/CategoryService.java

@@ -4,7 +4,6 @@ import org.springframework.stereotype.Service;
 import java.util.List;
 import java.util.UUID;
 
-
 @Service
 public class CategoryService {
     private CategoryRepository categoryRepository;
@@ -25,8 +24,11 @@ public class CategoryService {
     }
 
     public CategoryDto getCategoryById(UUID id) {
-        return CategoryDtoMapper.toDto(categoryRepository.getCategoryById(id));
+        Category c = categoryRepository.getCategoryById(id);
+        if (c == null) {
+            return null;
+        }
+        return CategoryDtoMapper.toDto(c);
     }
 
-
 }