This tutorial shows how to use Upstash with Redisson client. See code

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1 Create a Maven Project

Create a maven project and copy the following dependency to your pom.xml 
<dependency>
    <groupId>org.redisson</groupId>
    <artifactId>redisson</artifactId>
    <version>3.15.4</version>
</dependency>

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2 Create a Redis (Upstash) Database

Create a database as getting started

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3 Code

Create your java file and replace Redis password and URL below. If you enabled TLS, the endpoint should start with rediss 
public class Main {

    public static void main(String[] args) {
        Config config = new Config();
        config.useSingleServer().setPassword("YOUR_PASSWORD")
                // use "rediss://" for SSL connection
                .setAddress("YOUR_ENDPOINT");
        RedissonClient redisson = Redisson.create(config);
        RMap<String, String> map = redisson.getMap("map");
        map.put("foo", "bar");
        System.out.println(map.get("foo"));
    }
}