Spring Cloud Function Demo: Create and Deploy Serverless Functions with Spring Boot

This guide will show you how to create a simple Spring Boot project using Spring Cloud Function to implement a serverless function. You’ll learn how to set up a project, create a greeting function, expose it as a REST endpoint, and deploy it to a cloud environment like AWS Lambda or Azure Functions. By the end, you'll have a scalable, cloud-ready function. Let’s get started!

Step 1: Create a Spring Boot Project via Spring Initializr

1. Visit Spring Initializr: Go to https://start.spring.io/.

2. Configure Project Metadata:

   • Project: Maven Project
   • Language: Java
   • Spring Boot: 3.4.2 (or latest version compatible with your setup)
   • Project Metadata:
     • Group: com.example
     • Artifact: spring-cloud-function-demo
     • Name: spring-cloud-function-demo
     • Description: Demo project for Spring Cloud Function
     • Package Name: com.example.springcloudfunctiondemo
     • Packaging: Jar
     • Java Version: 17 (or any version compatible with Spring Boot 3.4.2)

3. Add Dependencies:

   • Spring Web
   • Function

4. Generate Project: Click Generate to download the zip file for the project.

Step 2: Unzip the Project and Open in Your IDE

Once the project is generated, unzip the file and open it in your IDE (e.g., IntelliJ IDEA, Eclipse, VS Code).

Step 3: Complete pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>3.4.2</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>
	<groupId>com.example</groupId>
	<artifactId>demo</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>demo</name>
	<description>Demo project for Spring Boot</description>
	<url/>
	<licenses>
		<license/>
	</licenses>
	<developers>
		<developer/>
	</developers>
	<scm>
		<connection/>
		<developerConnection/>
		<tag/>
		<url/>
	</scm>
	<properties>
		<java.version>17</java.version>
		<spring-cloud.version>2024.0.0</spring-cloud.version>
	</properties>
	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-function-context</artifactId>
		</dependency>

		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-test</artifactId>
			<scope>test</scope>
		</dependency>
	</dependencies>
	<dependencyManagement>
		<dependencies>
			<dependency>
				<groupId>org.springframework.cloud</groupId>
				<artifactId>spring-cloud-dependencies</artifactId>
				<version>${spring-cloud.version}</version>
				<type>pom</type>
				<scope>import</scope>
			</dependency>
		</dependencies>
	</dependencyManagement>

	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>

</project>

Step 4: Implement Your Function Bean

Create a simple function that processes input and produces output. For this example, we'll create a function that greets the user.

In the src/main/java/com/example/springcloudfunctiondemo directory, create a new Java class for the function:

package com.example.springcloudfunctiondemo;

import org.springframework.stereotype.Service;
import java.util.function.Function;

@Service
public class GreetingFunction implements Function<String, String> {

    @Override
    public String apply(String name) {
        return "Hello, " + name + "!";
    }
}

Step 5: Configure Function in application.properties

In the src/main/resources/application.properties file, you can define which function to use. This configuration ensures Spring Boot knows which function to route to:

spring.cloud.function.definition=greetingFunction

Step 6: Create a REST Controller to Expose the Function

To expose your function as an HTTP endpoint, create a @RestController class that maps a request to the function.

package com.example.springcloudfunctiondemo;

import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import java.util.function.Function;

@RestController
public class FunctionController {

    private final Function<String, String> greetingFunction;

    public FunctionController(Function<String, String> greetingFunction) {
        this.greetingFunction = greetingFunction;
    }

    @RequestMapping("/greet")
    public String greet(String name) {
        return greetingFunction.apply(name);
    }
}

Step 7: Main Application Class

Create a main class to run the Spring Boot application.

package com.example.springcloudfunctiondemo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class SpringCloudFunctionDemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(SpringCloudFunctionDemoApplication.class, args);
    }
}

Step 8: Run the Application

To run the application, use Maven or your IDE:

mvn spring-boot:run

Step 9: Test the Application

Once the application is running, open your browser or use curl to test the function:

http://localhost:8080/greet?name=John

You should see the following output:

Hello, John!

Step 10: Optional - Deploy to a Cloud Environment

Spring Cloud Function is designed for serverless environments like AWS Lambda, Google Cloud Functions, or Azure Functions. If you're deploying to AWS Lambda, you can configure the handler in your application.properties:

spring.cloud.function.aws.handler=com.example.springcloudfunctiondemo.GreetingFunction

You’ll need to add AWS Lambda dependencies and configuration for cloud deployment.