[EDIT] 名前で検索できる機能を追加しました。

src/main/java/com/example/demo/app/domain/service/CategoryService.java

@@ -9,4 +9,6 @@ public interface CategoryService {
 	public List<CategoryModel> findAll();
 	
 	public CategoryModel findOne(Long categoryId);
+	
+	public CategoryModel findOneByCategoryName(String categoryName);
 }

src/main/java/com/example/demo/app/domain/service/impl/CategoryServiceImpl.java

@@ -14,7 +14,7 @@ import lombok.RequiredArgsConstructor;
 
 @Service
 @RequiredArgsConstructor
-public class CategoryServiceImpl implements CategoryService{
+public class CategoryServiceImpl implements CategoryService {
 
 	private final CategoryRepository categoryRepository;
 
@@ -36,4 +36,16 @@ public class CategoryServiceImpl implements CategoryService{
 
 	}
 
+	public CategoryModel findOneByCategoryName(String categoryName) {
+
+		CategoryEntity categoryModel = categoryRepository.findByCategoryName(categoryName);
+
+		if (categoryModel == null) {
+			return null;
+		}
+
+		return CategoryModel.convertFrom(categoryModel);
+
+	}
+
 }