AWS Lambda Java Integration

Patterns for creating high-performance AWS Lambda functions in Java with optimized cold starts.

Overview

This skill provides complete patterns for AWS Lambda Java development, covering two main approaches:

1. Micronaut Framework - Full-featured framework with AOT compilation, dependency injection, and cold start < 1s
2. Raw Java - Minimal overhead approach with cold start < 500ms

Both approaches support API Gateway and ALB integration with production-ready configurations.

When to Use

• Deploying Java functions to AWS Lambda
• Optimizing cold starts below 1 second
• Choosing between Micronaut and Raw Java approaches
• Configuring API Gateway or ALB integration
• Setting up CI/CD pipelines for Java Lambda

Instructions

1. Choose Your Approach

Approach	Cold Start	Best For	Complexity
Micronaut	< 1s	Complex apps, DI needed, enterprise	Medium
Raw Java	< 500ms	Simple handlers, minimal overhead	Low

Validate: Confirm the approach fits your use case before proceeding.

2. Project Structure

my-lambda-function/
├── build.gradle (or pom.xml)
├── src/main/java/com/example/Handler.java
└── serverless.yml (or template.yaml)

Validate: Verify project structure matches the template.

3. Implementation Examples

Micronaut Handler

@FunctionBean("my-function")
public class MyFunction implements Function<APIGatewayProxyRequestEvent, APIGatewayProxyResponseEvent> {

    private final MyService service;

    public MyFunction(MyService service) {
        this.service = service;
    }

    @Override
    public APIGatewayProxyResponseEvent apply(APIGatewayProxyRequestEvent request) {
        // Process request
        return new APIGatewayProxyResponseEvent()
            .withStatusCode(200)
            .withBody("{\"message\": \"Success\"}");
    }
}

Raw Java Handler

public class MyHandler implements RequestHandler<APIGatewayProxyRequestEvent, APIGatewayProxyResponseEvent> {

    private static final MyService service = new MyService();

    @Override
    public APIGatewayProxyResponseEvent handleRequest(APIGatewayProxyRequestEvent request, Context context) {
        return new APIGatewayProxyResponseEvent()
            .withStatusCode(200)
            .withBody("{\"message\": \"Success\"}");
    }
}

Validate: Run

sam local invoke

to verify handler works before deployment.

Core Patterns

Connection Management

// Initialize once, reuse across invocations
private static final DynamoDbClient dynamoDb = DynamoDbClient.builder()
    .region(Region.US_EAST_1)
    .build();

// Avoid: Creating clients in handler (slow on every invocation)

Error Handling

@Override
public APIGatewayProxyResponseEvent handleRequest(APIGatewayProxyRequestEvent request, Context context) {
    try {
        return successResponse(process(request));
    } catch (ValidationException e) {
        return errorResponse(400, e.getMessage());
    } catch (Exception e) {
        context.getLogger().log("Error: " + e.getMessage());
        return errorResponse(500, "Internal error");
    }
}

Best Practices

Configuration

• Memory: Start with 512MB, adjust based on profiling
• Timeout: Micronaut 10-30s, Raw Java 5-10s
• Runtime: Java 17 or 21 for best performance

Packaging

• Use Gradle Shadow Plugin or Maven Shade Plugin
• Exclude unnecessary dependencies

Monitoring

• Enable X-Ray tracing for performance analysis
• Use CloudWatch Insights to track cold vs warm starts

Deployment Options

Serverless Framework

service: my-java-lambda
provider:
  name: aws
  runtime: java21
  memorySize: 512
  timeout: 10
package:
  artifact: build/libs/function.jar
functions:
  api:
    handler: com.example.Handler
    events:
      - http:
          path: /{proxy+}
          method: ANY

Validate: Run

serverless deploy

with

--stage dev

first.

AWS SAM

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Resources:
  MyFunction:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri: build/libs/function.jar
      Handler: com.example.Handler
      Runtime: java21
      MemorySize: 512
      Timeout: 10
      Events:
        ApiEvent:
          Type: Api
          Properties:
            Path: /{proxy+}
            Method: ANY

Validate: Run

sam validate

before deploying.

Constraints and Warnings

Java-Specific Constraints

• Reflection: Minimize use; prefer AOT compilation (Micronaut)
• Classpath scanning: Slows cold start; use explicit configuration
• Large frameworks: Spring Boot adds significant cold start overhead

Common Pitfalls

1. Initialization in handler - Causes repeated work on warm invocations
2. Oversized JARs - Include only required dependencies
3. Insufficient memory - Java needs more memory than Node.js/Python
4. No timeout handling - Always set appropriate timeouts

References

For detailed guidance on specific topics:

• Micronaut Lambda - Complete Micronaut setup, AOT configuration, DI optimization
• Raw Java Lambda - Minimal handler patterns, singleton caching, JAR packaging
• Serverless Deployment - Serverless Framework, SAM, CI/CD pipelines, provisioned concurrency
• Testing Lambda - JUnit 5, SAM Local, integration testing, performance measurement

Examples

Example 1: Create a Micronaut Lambda Function

Input:

Create a Java Lambda function using Micronaut to handle user REST API

Process:

1. Configure Gradle project with Micronaut plugin
2. Create Handler class extending MicronautRequestHandler
3. Implement methods for GET/POST/PUT/DELETE
4. Configure application.yml with AOT optimizations
5. Set up packaging with Shadow plugin
6. Validate: Test locally with SAM CLI before deploying

Output:

• Complete project structure
• Handler with dependency injection
• serverless.yml deployment configuration

Example 2: Optimize Cold Start for Raw Java

Input:

My Java Lambda has 3 second cold start, how do I optimize it?

Process:

1. Analyze initialization code
2. Move AWS client creation to static fields
3. Reduce dependencies in build.gradle
4. Configure optimized JVM options
5. Consider provisioned concurrency
6. Validate: Measure cold start with CloudWatch metrics after changes

Output:

• Refactored code with singleton pattern
• Minimized JAR
• Cold start < 500ms

Example 3: Deploy with GitHub Actions

Input:

Configure CI/CD for Java Lambda with SAM

Process:

1. Create GitHub Actions workflow
2. Configure Gradle build with Shadow
3. Set up SAM build and deploy
4. Add test stage before deployment
5. Configure environment protection for prod

Output:

• Complete .github/workflows/deploy.yml
• Multi-stage pipeline (dev/staging/prod)
• Integrated test automation

Version

Version: 1.0.0