This guide will walk you through the best practices of using Java on AWS Lambda. To understand and implement these best practices, you will go over the history of Java, evolution of computing, and the challenges we face building serverless Java applications on AWS Lambda.

Simple Java Lambda function

A simple Java Lambda function would look like the following:

package com.example;

public class HelloHandler {
  public HelloResponse handleRequest(HelloRequest request) {
    String message = "Hello " + request.getName();
    
    HelloResponse response = new HelloResponse();
    response.setMessage(message);
    
    return response;
  }
}

Advanced usage of a Lambda function would involve additional dependencies which you would normally use for production grade applications. Here are some of those core dependencies:

• com.amazonaws:aws-lambda-java-core which provides the handler interfaces, and context object.
• com.amazonaws:aws-lambda-java-events which provides input types for events from AWS services.

Here is an example using handler interface:

public class App implements RequestHandler<RequestEvent, ResponseEvent> {
  
  public ResponseEvent handleRequest(RequestEvent event, Context context) {
    // Process incoming event payload
    
    return ResponseEvent().builder()
      .withStatusCode(200)
      .withBody("Hello World")
      .build();
  }
}

Here is an example of using aws-lambda-java-events library to serialize incoming events from Amazon API Gateway, Amazon SQS, and Amazon S3:

Amazon API Gateway

import com.amazonaws.services.lambda.runtime.events.APIGatewayProxyRequestEvent;
import com.amazonaws.services.lambda.runtime.events.APIGatewayProxyResponseEvent;

public class UnicornRequestHandler implements RequestHandler<APIGatewayProxyRequestEvent, APIGatewayProxyResponseEvent> {
  
  @Override
  public APIGatewayProxyResponseEvent handleRequest(APIGatewayProxyRequestEvent event, Context context) { }
}

Amazon SQS

import com.amazonaws.services.lambda.runtime.events.SQSEvent;
import com.amazonaws.services.lambda.runtime.events.SQSBatchResponse;

public class UnicornQueueProcessor implements RequestHandler<SQSEvent, SQSBatchResponse> {
  
  @Override
  public SQSBatchResponse handleRequest(SQSEvent event, Context context) { }
}

Amazon S3

import com.amazonaws.services.lambda.runtime.events.S3Event;

public class UnicornDocumentHandler implements RequestHandler<S3Event, String> {
  
  @Override
  public String handleRequest(S3Event event, Context context) { }
}

Before we dive deeper into best practices, let's take a look at the history of Java and computing which will help understand why AWS Lambda specific best practices are necessary.