Invoking REST APIs in a Spring Boot Application using Command Line Inputs

Learn how to effectively invoke `REST APIs` in a Spring Boot application using command line inputs, leveraging the power of the `CommandLineRunner` interface.
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Invoking REST APIs in a Spring Boot Application using Command Line Inputs

In recent years, Spring Boot has become one of the most popular frameworks for building Java applications, particularly for RESTful services. However, a common challenge many developers face is how to invoke REST APIs directly from the command line during runtime. In this guide, we’ll explore how to set up your Spring Boot application to handle command line input and subsequently invoke specific REST APIs based on that input.

The Challenge

Suppose you want to create a Spring Boot application that allows users to perform various mathematical operations (like addition) by entering commands in the command line. For instance, if the user inputs add 2 3, your application should invoke the corresponding REST API to execute the addition. This functionality typically requires listening for user input after the application has started, which is somewhat unconventional since the CommandLineRunner interface is frequently used to run code at application startup.

Solution Overview

To achieve this functionality, we'll leverage Spring's RestTemplate alongside the CommandLineRunner interface. This combination will allow us to listen for user input and make RESTful calls to the desired endpoints based on that input.

Step-by-Step Implementation

Create the REST Controller:
First, create a REST controller that handles the addition operation. This controller will define the endpoint that you will call from the command line input. Here’s an example:

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Define the CommandLineRunner:
Next, implement the CommandLineRunner interface in your Spring Boot application to capture user input from the command line. This is where we integrate the RestTemplate to invoke the REST API based on user input.

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Define the Entity Class:
You’ll also need a simple Java class to represent the data you’re sending in the request body.

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Configure the RestTemplate:
Finally, don’t forget to configure a RestTemplate bean in your Spring Boot application to allow for API calls.

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Conclusion

By utilizing the CommandLineRunner interface in combination with RestTemplate, you can successfully invoke REST APIs in a Spring Boot application based on user input from the command line. This opens up a myriad of possibilities for dynamic interaction with your application.

Now you can extend this logic to handle more operations or even complex command parsing based on your application needs.

Do you have questions or suggestions to enhance this functionality? Feel free to share your thoughts in the comments below!