Spring Cloud Function with Spring Boot Tutorial

Introduction

Spring Cloud Function is a project that aims to promote the development of event-driven functions in a cloud-native way. It allows developers to write functions that can be deployed and executed in various environments, including serverless platforms. This tutorial will walk you through creating a simple Spring Boot application that utilizes Spring Cloud Function.

Prerequisites

Before you start, ensure you have the following installed on your machine:

• Java Development Kit (JDK) 11 or later
• Apache Maven
• An IDE (e.g., IntelliJ IDEA, Eclipse)
• Basic knowledge of Spring Boot and Maven

Setting Up the Project

We will create a new Spring Boot project using Spring Initializr. Follow these steps:

1. Visit Spring Initializr.
2. Select the following options:
• Project: Maven Project
• Language: Java
• Spring Boot: 2.5.0 or later
• Packaging: Jar
• Java: 11 or later
3. In the Dependencies section, add:
• Spring Web
• Spring Cloud Function
4. Click on the "Generate" button to download the project.

Extract the downloaded ZIP file and open it in your IDE.

Creating a Simple Function

Let’s create a simple function that takes a string input and returns it in uppercase. Create a new Java class named UppercaseFunction.java in the src/main/java/com/example/demo directory.

package com.example.demo;

import org.springframework.cloud.function.context.FunctionRegistry;
import org.springframework.stereotype.Component;

import java.util.function.Function;

@Component
public class UppercaseFunction implements Function {
    @Override
    public String apply(String input) {
        return input.toUpperCase();
    }
}
                

This class implements the Function interface and overrides the apply method to convert the input string to uppercase.

Configuring Application Properties

Open the application.properties file located at src/main/resources and add the following configuration:

spring.cloud.function.definition=uppercaseFunction
                

This property tells Spring Cloud Function to use the uppercaseFunction as the default function to execute.

Creating a REST Controller

Next, create a REST controller that will expose an endpoint to invoke the function. Create a new class named FunctionController.java in the same package.

package com.example.demo;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.cloud.function.web.FunctionController;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class FunctionController {
    
    @Autowired
    private FunctionController functionController;

    @PostMapping("/uppercase")
    public String uppercase(@RequestBody String input) {
        return functionController.apply(input);
    }
}
                

The FunctionController class defines a POST endpoint that receives a string and invokes the uppercase function.

Running the Application

To run your application, open a terminal, navigate to your project directory, and execute the following command:

The application will start on http://localhost:8080.

Testing the Function

You can test your function using tools like Postman or cURL. Here’s how to do it using cURL:

You should receive the following output:

Conclusion

In this tutorial, we have covered the basics of creating a Spring Cloud Function with Spring Boot. We created a simple function that transforms input text to uppercase, set up a REST controller, and tested the function. Spring Cloud Function provides a powerful way to develop and deploy functions in a cloud-native environment.