spring-cloud-function

What this skill does

# Spring Cloud Function - Quick Reference

> **Deep Knowledge**: Use `mcp__documentation__fetch_docs` with technology: `spring-cloud-function` for comprehensive documentation.

## Dependencies

```xml
<!-- Core -->
<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-function-web</artifactId>
</dependency>

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

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

<!-- GCP Cloud Functions adapter -->
<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)
```java
@Configuration
public class FunctionConfig {

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

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

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

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

### Consumer (Input → void)
```java
@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)
```java
@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
```yaml
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

```java
// 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
```java
@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

```java
// 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
```yaml
# AWS Lambda handler
spring:
  cloud:
    function:
      definition: processEvent
```

### Lambda Handler Class
```java
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
```yaml
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
```java
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

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

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

## Function Catalog

```java
@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

```java
@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 ord