Spring Cloud Function - Quick Reference

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Dependencies

<dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-starter-function-web</artifactId> </dependency>

<dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-function-adapter-aws</artifactId> </dependency>

<dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-function-adapter-azure</artifactId> </dependency>

<dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-function-adapter-gcp</artifactId> </dependency>

Function Types

┌─────────────────────────────────────────────────────────────┐ │ Function Types │ │ │ │ Function<I, O> Input → Processing → Output │ │ Consumer<I> Input → Processing (no output) │ │ Supplier<O> (no input) → Generate Output │ │ │ │ ┌───────┐ ┌──────────┐ ┌────────┐ │ │ │ Input │───▶│ Function │───▶│ Output │ │ │ └───────┘ └──────────┘ └────────┘ │ └─────────────────────────────────────────────────────────────┘

Basic Functions

Function (Input → Output)

@Configuration public class FunctionConfig {

@Bean
public Function&#x3C;String, String> uppercase() {
    return value -> value.toUpperCase();
}

@Bean
public Function&#x3C;Person, Greeting> greet() {
    return person -> new Greeting("Hello, " + person.getName() + "!");
}

@Bean
public Function&#x3C;Flux&#x3C;String>, Flux&#x3C;String>> reactiveUppercase() {
    return flux -> flux.map(String::toUpperCase);
}

}

public record Person(String name, int age) {} public record Greeting(String message) {}

Consumer (Input → void)

@Bean public Consumer<Order> processOrder() { return order -> { log.info("Processing order: {}", order.getId()); orderService.process(order); }; }

@Bean public Consumer<Flux<Event>> eventProcessor() { return events -> events .doOnNext(event -> log.info("Received event: {}", event)) .subscribe(eventService::handle); }

Supplier (void → Output)

@Bean public Supplier<String> hello() { return () -> "Hello, World!"; }

@Bean public Supplier<Flux<Long>> counter() { return () -> Flux.interval(Duration.ofSeconds(1)); }

@Bean public Supplier<List<Product>> getProducts() { return () -> productRepository.findAll(); }

Configuration

application.yml

spring: cloud: function: # Default function to invoke definition: uppercase

  # For multiple functions
  # definition: validate|process|notify

  # Routing based on header
  routing-expression: "headers['function-name']"

Function-specific config

uppercase: prefix: "RESULT: "

Function Composition

// Compose functions @Bean public Function<String, String> validate() { return input -> { if (input == null || input.isEmpty()) { throw new IllegalArgumentException("Input cannot be empty"); } return input; }; }

@Bean public Function<String, String> sanitize() { return input -> input.trim().toLowerCase(); }

@Bean public Function<String, String> process() { return input -> "Processed: " + input; }

// Configuration to compose: validate|sanitize|process // spring.cloud.function.definition=validate|sanitize|process

Programmatic Composition

@Bean public Function<String, String> composedFunction( Function<String, String> validate, Function<String, String> sanitize, Function<String, String> process) {

return validate.andThen(sanitize).andThen(process);

}

HTTP Endpoints

// Automatic HTTP endpoints when using spring-cloud-starter-function-web // POST /uppercase → invokes uppercase function // POST /greet → invokes greet function // GET /hello → invokes hello supplier

// Example requests: // curl -X POST localhost:8080/uppercase -d "hello" -H "Content-Type: text/plain" // curl -X POST localhost:8080/greet -d '{"name":"John"}' -H "Content-Type: application/json" // curl localhost:8080/hello

AWS Lambda

Handler Configuration

AWS Lambda handler

spring: cloud: function: definition: processEvent

Lambda Handler Class

public class LambdaHandler extends FunctionInvoker<APIGatewayProxyRequestEvent, APIGatewayProxyResponseEvent> { }

@Bean public Function<APIGatewayProxyRequestEvent, APIGatewayProxyResponseEvent> processEvent() { return request -> { String body = request.getBody(); // Process request return APIGatewayProxyResponseEvent.builder() .statusCode(200) .body("Processed: " + body) .build(); }; }

SAM Template

AWSTemplateFormatVersion: '2010-09-09' Transform: AWS::Serverless-2016-10-31

Resources: MyFunction: Type: AWS::Serverless::Function Properties: Handler: org.springframework.cloud.function.adapter.aws.FunctionInvoker::handleRequest Runtime: java17 CodeUri: target/my-function.jar MemorySize: 512 Timeout: 30 Environment: Variables: SPRING_CLOUD_FUNCTION_DEFINITION: processEvent Events: Api: Type: Api Properties: Path: /process Method: POST

Azure Functions

Host Configuration

public class AzureHandler extends FunctionInvoker<HttpRequestMessage<String>, HttpResponseMessage> { }

@FunctionName("process") public HttpResponseMessage run( @HttpTrigger( name = "req", methods = {HttpMethod.POST}, authLevel = AuthorizationLevel.ANONYMOUS ) HttpRequestMessage<String> request, ExecutionContext context) {

return handleRequest(request, context);

}

GCP Cloud Functions

public class GcpHandler extends FunctionInvoker<String, String> { }

// Deployment // gcloud functions deploy myFunction
// --entry-point org.springframework.cloud.function.adapter.gcp.FunctionInvoker
// --runtime java17
// --trigger-http
// --memory 512MB

Message-Driven Functions

With Spring Cloud Stream

@Bean public Function<Flux<Order>, Flux<OrderResult>> processOrders() { return orders -> orders .map(order -> { // Process order return new OrderResult(order.getId(), "PROCESSED"); }); }

spring: cloud: stream: bindings: processOrders-in-0: destination: orders processOrders-out-0: destination: order-results function: definition: processOrders

Function Catalog

@Autowired private FunctionCatalog functionCatalog;

public void invokeDynamically(String functionName, Object input) { Function<Object, Object> function = functionCatalog.lookup(functionName); if (function != null) { Object result = function.apply(input); log.info("Result: {}", result); } }

Error Handling

@Bean public Function<Order, OrderResult> processOrder() { return order -> { try { validateOrder(order); return new OrderResult(order.getId(), "SUCCESS"); } catch (ValidationException e) { return new OrderResult(order.getId(), "VALIDATION_ERROR: " + e.getMessage()); } catch (Exception e) { log.error("Error processing order", e); throw new RuntimeException("Processing failed", e); } }; }

// Global error handler @Bean public Consumer<ErrorMessage> errorHandler() { return error -> { log.error("Function error: {}", error.getPayload().getMessage()); alertService.sendAlert(error); }; }

Testing

@SpringBootTest class FunctionTests {

@Autowired
private Function&#x3C;String, String> uppercase;

@Autowired
private FunctionCatalog catalog;

@Test
void shouldUppercase() {
    String result = uppercase.apply("hello");
    assertThat(result).isEqualTo("HELLO");
}

@Test
void shouldLookupFunction() {
    Function&#x3C;String, String> fn = catalog.lookup("uppercase");
    assertThat(fn.apply("test")).isEqualTo("TEST");
}

@Test
void shouldComposeFunction() {
    Function&#x3C;String, String> composed = catalog.lookup("validate|sanitize|process");
    String result = composed.apply("  HELLO  ");
    assertThat(result).isEqualTo("Processed: hello");
}

}

// Integration test with WebTestClient @SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT) class FunctionHttpTests {

@Autowired
private WebTestClient webTestClient;

@Test
void shouldInvokeViaHttp() {
    webTestClient.post()
        .uri("/uppercase")
        .contentType(MediaType.TEXT_PLAIN)
        .bodyValue("hello")
        .exchange()
        .expectStatus().isOk()
        .expectBody(String.class)
        .isEqualTo("HELLO");
}

}

Native Image (GraalVM)

<dependency> <groupId>org.springframework.experimental</groupId> <artifactId>spring-native</artifactId> </dependency>

<plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> <configuration> <image> <builder>paketobuildpacks/builder:tiny</builder> <env> <BP_NATIVE_IMAGE>true</BP_NATIVE_IMAGE> </env> </image> </configuration> </plugin>

Best Practices

Do Don't

Keep functions focused/small Create monolithic functions

Use reactive types for streaming Block on large datasets

Handle errors gracefully Let exceptions propagate unhandled

Test functions in isolation Skip unit tests

Configure appropriate timeouts Ignore cold start impact

Production Checklist

Function definition configured
Error handling implemented
Timeouts appropriate for platform
Memory limits set
Cold start optimized
Logging configured
Monitoring/tracing enabled
Secrets management (not env vars)
Native image if needed
CI/CD pipeline for deployment

When NOT to Use This Skill

REST APIs - Use standard Spring MVC controllers
Complex workflows - Use AWS Step Functions, Temporal
Long-running processes - Not suitable for functions
Traditional deployment - May not provide benefits

Anti-Patterns

Anti-Pattern Problem Solution

Large function payload Cold start, timeout Keep functions small

State in function Functions should be stateless Use external storage

Hardcoded cloud config Not portable Use Spring Cloud abstractions

No timeout handling Lambda timeout = error Handle gracefully

Secrets in env vars Security risk Use secrets manager

Quick Troubleshooting

Problem Diagnostic Fix

Function not found Check function name Verify spring.cloud.function.definition

Cold start slow Check dependencies Reduce classpath, use native

Timeout Check execution time Optimize or increase timeout

Memory error Check Lambda config Increase memory allocation

Routing not working Check function catalog Verify function names

Reference Documentation

Spring Cloud Function Reference

spring-cloud-function

Safety Notice

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Function-specific config

AWS Lambda handler

Source Transparency

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