We will create a back-end of a very important feature in every e-Commerce site — Wishlist, using Java and Spring Boot

A Wishlist is an eCommerce feature that allows shoppers to create personalized collections of products they want to buy and save them in their user account. It is a must-have feature for eCommerce applications.
We will first develop the back-end API using Java & Spring Boot (in this tutorial). After the API has been created, we will use that API in our Vue.Js front-end and Android front-end (in other tutorials).

Youtube Discussion

Live Demo

You can test the API at the following swagger link. You will find the wishlist API in wish-list-controller section.
Swagger UI
You can find the complete code at Github.

Pre-requisites

1. Knowledge of Java, OOP & Spring Boot Framework
2. Java Development Kit (JDK)
3. IntelliJ IDEA Ultimate — open-source (Recommended)
4. MySQL/MariaDB Database
5. A good browser (Chrome — recommended) This tutorial is part of our series on Back-end Development with Java. We will extend the code which we developed in the previous tutorials in this series. So, if you have any doubt regarding anything that we developed earlier, you can read about it in the corresponding tutorial in the series. ## Project Structure If you have not read the previous tutorials in the back-end series, don’t worry. This section is specifically for you. As we will use the project structure that we created in the previous tutorials, we intend to describe the structure here before we begin working on the Wishlist feature. This will help you in understanding the code in a better way. Following is the project structure:

   

   We will now describe the following directories:-
   1. controller— contains the controllers for various API endpoints
   2. dto — contains the Data Transfer Objects (DTO) for our back-end. In client-server projects, data is often structured differently. There are some details in the database that we do not want to send as a response to the API calls. So, the server stores its information in a database-friendly way. While retrieving that information from the database, it can use DTOs to filter this information and then send it to the client. Don’t worry if you could not understand DTOs. You will understand it when we implement Wishlist DTO in this tutorial.
   3. model — contains the data models (and entities)
   4. repository — contains the methods for CRUD operations in corresponding tables of the database
   5. service — contains the class files with @service annotations. These class files are used to write business logic in a different layer, separated from @RestController class files. Business logic or domain logic is that part of the program which encodes the real-world business rules that determine how data can be created, stored, and changed inside the database. ## API Design Before we begin to code, we must spend some time to think about the API design and the database design. Let’s begin with the API design. Currently, we need only two API endpoints:-
   6. Adding to wishlist
   7. Getting wishlist Also, we had already added the token-based authorization in our eCommerce backend. So, instead of user id, we will pass the token to every endpoint of the API. Hence, we decide to have the following endpoints. Also, in the body of the POST method, we will have to send the id of the product so that the given product can be added to the corresponding user’s wishlist. Hence, the body of the POST request should look like the following Now, the response of the POST request should send the list of all products in the wishlist with the necessary details. Hence, the response should look like the following ## Table Design Now, let’s discuss the table design. We had already created the ecommerce database in previous tutorials. In this database, we will create a new table called wishlist. We will keep the design simple. The database should have three columns — id, user_id, product_id,created_date. Here,
   8. id is the primary key and will be auto-generated
   9. user_id — stores userId
   10. product_id — stores the product id
   11. created_date — stores the data & time at which the entry was created The schema of the database looks like the following:-
       Ideally, each user’s wishlist should have a particular product only once. But for simplicity, we are not considering such cases. ## Let’s Code We will now begin to write code. ## Model (Entity) Let’s begin with writing the code for the Model class of each entry in the wishlist table. If you are familiar with Spring Boot or any other MVC framework, you would know that Model class is used to store each entry of the table. In Spring Boot, we use Annotations to map the columns of the table with the class members. To create the model class, create a new class inside the Model directory. We will call this class — WishList.
   12. We have already described the schema of the table. Using the schema, we will create the class variables of the model class representing each column of the database.
   13. We will also create one class object of Product class. This object will store all the details of the product like name, price, description etc.
   14. Also, note that the column created_date should be filled with the current date and time. For this, we will use the java.util.Date class. Following is the complete code of WishList.java
       ## Repository It is time to create the repository interface for the wishlist table. Create a new file called WishListRepository.java inside the Repository directory. If you are familiar with Spring Boot, you would know that Repository the interface contains methods to fetch data from the table. Creating CRUD methods manually means writing a lot of boilerplate code unless you let the JPARepository interface carry about routine implementations for you. So, we will extend the JPARepository and create the interface WishListRepository.
   15. Extending JPARepository will automatically create and implement methods for the basic CRUD operations.
   16. We will define a method findAllByUserIdOrderByCreatedDateDesc() to fetch the wishlist of a user and order the list by created the date of each entry in the wishlist. The implementation of this method will be managed automatically by the JPARepository. Following is the complete code of WishListRepository.java
       ## Service Now, let's implement the Service class to interact with the wishlist table. In the WishListRepository interface, we defined the methods to interact with the database. In the Service class, we will call these methods and implement the so-called business logic. To keep things simple, we do not have any business logic, i.e. business constraints or rules defined. So, we will simply create two methods createWishlist() and readWishlist() . Inside these methods, we will call the methods defined in the WishListRepository interface. Following is the complete code of WishListService.java
       ## Controller Now, Let’s begin with writing code for the controller. If you are familiar with Spring Boot or any other MVC framework, you would already know that controller defines the endpoints of the API. Create a new file inside the Controller directory with the name WishlistController.java . Since we have two endpoints, we will create two methods in the WishlistController class.
   17. To use the WishListService and AuthenticationService , we will create the two objects of respective types. We have already created the WishListService in the previous section and is used to interact with the database. We created AuthenticationService in a previous tutorial and is used to fetch user id of the corresponding token
   18. We will create one method with @GetMapping for the GET request and @PostMapping for the POST request.
   19. Now, each table entry contains the created_date value also. We do not want to send that with the response. So, here comes the use of DTO. Using the getDtoFromProduct() method of the ProductService Class, we will store only that information about each product which we want to send as response. Hence, we create a list of ProductDto object and store only the required details. We will send this list in the response. The following is the complete code of WishlistController.java
       ## Congratulations!!! Congratulations, we have now added the wishlist feature to our backend. ## Suggested PRs If you wish to contribute to our eCommerce-backend, you clone this Github repository and work on the following features related to the wishlist
   20. Create an API end-point for Deleting a Product from Wishlist After you have implemented the feature, send us a PR. We will review and merge it into our master branch ## Reference
       

       Let’s Develop an E-Commerce Application From Scratch Using Java and Spring | by Nil Madhab | Javarevisited | Medium

       Nil Madhab ・ Jun 10, 2022 ・

       Medium

       

       Let’s Build Signup, SignIn, and Role-Based Access in Our E-Commerce App | by Nil Madhab | Javarevisited | Medium

       Nil Madhab ・ Apr 16, 2021 ・

       Medium

       

       Add Products for Ecommerce | Medium

       Nil Madhab ・ Apr 16, 2021 ・

       Medium