Serverless API with Java and Redis - Upstash Documentation

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.

Prerequisites

Install the Serverless Framework installed with an AWS account set up.

npm i serverless@3.39.0 -g

Install JDK and not Java JRE. Set your JAVA_HOME.
Install Apache Maven.
Create a free Serverless Redis database from Upstash as described here.

Project Setup

Create the project:

serverless create --template aws-java-maven --name counter-api -p aws-java-counter-api

cd aws-java-counter-api

Add jedis as dependency to the pom.xml:

pom.xml

...    <dependency>        <groupId>redis.clients</groupId>        <artifactId>jedis</artifactId>        <version>3.6.0</version>    </dependency>...

Update serverless.yml as below:

serverless.yml

service: counter-apiframeworkVersion: '3'provider:  name: aws  runtime: java17package:  artifact: target/hello-dev.jarfunctions: hello:   handler: com.serverless.Handler   events:     - httpApi:         path: /hello         method: get

Counter Function Setup

Update src/main/java/com/serverless/Handler.java as below:

src/main/java/com/serverless/Handler.java

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("lasting-roughy-29092.upstash.io", 6379, true);		jedis.auth("********");		Long value = jedis.incr("counter");		jedis.close();		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 Redis Console -> Your Database -> Connect to your database -> Java.

Build and Deploy

Build your project:

mvn clean install

Deploy to AWS:

serverless deploy

Visit the output URL to see the counter in action.