In this tutorial, we will build a stateful serverless API using Java and Redis on AWS Lambda. The API will simply count the page views and return it as http response.

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Prerequisites

  • Install node and npm
  • Install the Serverless Framework installed with an AWS account set up.
  • Install JDK and not Java JRE. Set your JAVA_HOME.
  • Install Apache Maven.
  • Create a free Serverless Redis database from Upstash as described here.

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Project Setup

  • Create the project:
serverless create —template aws-java-maven —name serverless-api-java-redis -p serverless-api-java-redis
  • Add jedis as dependency to the pom.xml: 
    <dependency>
   <groupId>redis.clients</groupId>
   <artifactId>jedis</artifactId>
   <version>3.6.0</version>
</dependency>
  • Update serverless.yml adding an http endpoint as below: 
functions:
 hello:
   handler: com.serverless.Handler
   events:
     - httpApi:
         path: /hello
         method: get

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The Code

Update Handler.java as below: 
package com.serverless;

import java.util.Map;

import com.amazonaws.services.lambda.runtime.Context;
import com.amazonaws.services.lambda.runtime.RequestHandler;
import redis.clients.jedis.Jedis;

public class Handler implements RequestHandler<Map<String, Object>, ApiGatewayResponse> {
  @Override
  public ApiGatewayResponse handleRequest(Map<String, Object> input, Context context) {
     Jedis jedis = new Jedis("us1-lasting-lion-32618.upstash.io", 32618, true);
     jedis.auth("d5033b46dfbgheb6718f9dbbd2925");
     Long value = jedis.incr("counter");
     String message = "Hello World, Count:" + value;
     return ApiGatewayResponse.builder()
           .setStatusCode(200)
           .setObjectBody(message)
           .build();
  }
}
In the above code, you need to replace your Redis endpoint and password. You can copy Jedis connection code from the Upstash console.

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Deploy and Run

First build your project with mvn clean install. Then deploy to AWS with serverless deploy. The last command will output the endpoint URL as below: 
Serverless: Stack update finished...

Service Information

service: serverless-api-java-redis

stage: dev

region: us-east-1

stack: serverless-api-java-redis-dev

resources: 11

api keys:

  None

endpoints:

  GET - https://60tinzba0a.execute-api.us-east-1.amazonaws.com/hello

functions:

  hello: serverless-api-java-redis-dev-hello

layers:

  None