1. What is Spring Cloud Function?

Spring Cloud Function is a framework that allows you to develop serverless applications in Java using Spring Boot. It provides a simple programming model for writing functions that can be triggered by events such as HTTP requests, database changes, or messaging.

2. Setup the Spring Boot Project

• Project: Maven (or Gradle)
• Dependencies:
  • Spring Web
  • Spring Cloud Function Web
  • (Optional) AWS Lambda for serverless deployment

	<dependencies>
    <!-- Spring Boot Web for REST API -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    
    <!-- Spring Cloud Function for serverless support -->
    <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-starter-function-web</artifactId>
    </dependency>
    
    <!-- Optional: AWS Lambda support 
    <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-starter-aws-lambda</artifactId>
    </dependency>
	-->
</dependencies>

a simple function that converts a string to uppercase. This function will be triggered via an HTTP request.

Step 1: Define the Function

Create a class UppercaseFunction.java that implements the Function interface from Java's java.util.function package.

	
package com.example.serverless;

import org.springframework.cloud.function.adapter.aws.SpringBootRequestHandler;
import org.springframework.stereotype.Component;

import java.util.function.Function;

@Component
public class UppercaseFunction implements Function<String, String> {

    @Override
    public String apply(String input) {
        return input != null ? input.toUpperCase() : "Input is null";
    }
}

• The function takes a string as input and returns the uppercase version.
• If the input is null, it returns "Input is null."

Step 2: Create Function Configuration

In Spring Cloud Function, you can define beans for each function.
The function will be mapped to an endpoint automatically by Spring Cloud Function Web.

package com.example.serverless;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class FunctionConfig {

    @Bean
    public UppercaseFunction uppercaseFunction() {
        return new UppercaseFunction();
    }
}

Step 3: Create the Spring Boot Application

package com.example.serverless;

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

@SpringBootApplication
public class Application {

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

You can bluid the application and run it manually

Build application- mvn clean install

Run application- java -jar target/yourapp.jar

step 4 Exposing the Function via HTTP

Spring Cloud Function automatically maps functions to HTTP endpoints. By default, it uses the function name as the endpoint.

GET http://localhost:8080/uppercaseFunction/hello

Result:

HELLO

you can use GET , POST

Example 2: JSON Parsing

Let’s create a function that processes JSON data:

package com.example.serverless;

import java.util.function.Function;

@Component
public class GreetingFunction implements Function<Person, String> {

    @Override
    public String apply(Person person) {
        return "Hello, " + person.getName() + "!";
    }
}

Person.java :

package com.example.serverless;

public class Person {
    private String name;

    // Getters and setters

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

add it to FunctionConfig.Java

package com.example.functionTestApp;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class FunctionConfig {

    @Bean
    public UppercaseFunction uppercaseFunction() {
        return new UppercaseFunction();
    }
    
   
    
    @Bean
    public GreetingFunction greetingFunction() {
        return new GreetingFunction();
    }
    
    
    
}

Test it: POST: http://localhost:8080/greetingFunction

{
    "name": "John"
}

Response:

Hello, John!