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Discover best practices for `integrating external APIs` in your Spring Boot Web MVC application with essential tips on architecture and error handling.
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A Comprehensive Guide to Calling External API from Your Spring Boot Web UI

As the landscape of software development evolves, many applications are transitioning from traditional database connections to leveraging external APIs for data management. If you're working on a Spring Boot WebMVC application with Thymeleaf and wondering how to architecture your API calls effectively, you're in the right place!

In this guide, we’ll address the best practices for calling external APIs from your Spring Boot application. We will break down the core components and answer common questions about placement of your API call logic and error handling.

Understanding the Basics

The Challenge

You are developing a Spring Boot application that will make calls to an external API rather than relying solely on a database connection. The main considerations revolve around:

Where to place the API call in your application: Should it reside in the Service class or the Controller class?

Whether to use RestTemplate or WebClient for handling API interactions.

Current Application Structure

To provide clarity, let’s look at an example structure of your application:

Entity Class

The entity class represents the data structure we are working with:

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Service Class

The service class manages the API interactions:

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Controller Class

The controller handles HTTP requests and responses:

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Thymeleaf Template (HTML)

The corresponding HTML code for displaying the entities might look like this:

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Deciding on the Architecture

Where to Place Your API Calls

The choice between placing your API calls in the Controller or Service class often boils down to:

App Complexity: If your application has minimal API interactions, a Service layer might introduce unnecessary complexity. However, as your application scales, a Service layer can help manage logic and keep Controllers tidy.

Best Practices: It’s advisable to keep Controllers focused on HTTP specifics (e.g., response codes, headers) and delegate business logic and API calls to the Service layer. This structure promotes cleaner code and simplifies maintenance.

Choosing Between RestTemplate and WebClient

RestTemplate: This is a blocking client that works well in traditional Spring applications. If you are building a synchronous application, this is a good choice.

WebClient: This is a non-blocking, reactive client introduced in Spring 5 aimed at building applications with asynchronous capabilities. Even if your application isn’t reactive, it offers advanced features that might be beneficial as the app evolves.

Grouping Your Code Intuitively

Instead of following a conventional package structure that separates controllers, services, and models, consider grouping these components based on the business context. This way, everything related to an Entity (controller, service, and model) will reside together, enhancing clarity and maintainability:

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Final Thoughts

As your application expands, don’t hesitate to refactor. Reliable tests will safeguard your architecture during changes, allowing you to replace RestTemplate with WebClient if needed or restructure components based on evolving requirements.

Focus on clear architecture and maintainability to ensure that your Spring Boot application is robust, scalable, and easy to understand for yourself and future contributors!

Keep Learning!

Working with external APIs can be complex, but breaking it into manageable parts and understanding the underlying principles will help yo