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.