[EDIT] EntityからModelへの変換メソッドを作成しました。

src/main/java/com/example/demo/app/domain/model/CategoryModel.java

@@ -1,5 +1,9 @@
 package com.example.demo.app.domain.model;
 
+import java.util.List;
+
+import com.example.demo.app.infra.entity.CategoryEntity;
+
 import lombok.AllArgsConstructor;
 import lombok.Getter;
 
@@ -11,4 +15,16 @@ public class CategoryModel {
 	private String categoryName;
 	private Integer transactionType;
 	
+	
+	public static CategoryModel convertFrom(CategoryEntity categoryEntity) {
+		return new CategoryModel(
+				categoryEntity.getCategoryId(),
+				categoryEntity.getCategoryName(),
+				categoryEntity.getTransactionType());
+	}
+
+	public static List<CategoryModel> convertFrom(List<CategoryEntity> categoryEntityList) {
+		return categoryEntityList.stream().map(CategoryModel::convertFrom).toList();
+	}
+	
 }

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

@@ -0,0 +1,10 @@
+package com.example.demo.app.domain.service;
+
+import java.util.List;
+
+import com.example.demo.app.domain.model.CategoryModel;
+
+public interface CategoryService {
+
+	public List<CategoryModel> findAll();
+}

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

@@ -0,0 +1,25 @@
+package com.example.demo.app.domain.service.impl;
+
+import java.util.List;
+
+import org.springframework.stereotype.Service;
+
+import com.example.demo.app.domain.model.CategoryModel;
+import com.example.demo.app.domain.service.CategoryService;
+import com.example.demo.app.infra.repository.CategoryRepository;
+
+import lombok.RequiredArgsConstructor;
+
+@Service
+@RequiredArgsConstructor
+public class CategoryServiceImpl implements CategoryService{
+
+	private final CategoryRepository categoryRepository;
+	
+	public List<CategoryModel> findAll() {
+		
+		return CategoryModel.convertFrom(categoryRepository.findAll());
+		
+	}
+	
+}