In this unit, we'll demonstrate how to manage user data with expiration using Java. You will be employing Lettuce as your primary Redis client library. The lesson will cover two main operations for user data management:

1. Adding user data with an expiration time: This operation ensures user data is available for a limited time and is automatically deleted afterward. Redis handles expired keys by deleting them when accessed after expiration (lazy deletion) and by periodically scanning and removing them in the background (active expiration) to free up memory.
2. Retrieving user data: This operation will facilitate fetching the stored user data.

Here’s an example of how we will structure these operations in Java using Lettuce:

Java
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1import io.lettuce.core.RedisClient;
2import io.lettuce.core.api.StatefulRedisConnection;
3import io.lettuce.core.api.sync.RedisCommands;
4import java.time.Duration;
5
6public class UserDataManager {
7    public static void main(String[] args) {
8        // Connect to Redis server
9        RedisClient redisClient = RedisClient.create("redis://localhost:6379");
10        StatefulRedisConnection<String, String> connection = redisClient.connect();
11        RedisCommands<String, String> syncCommands = connection.sync();
12
13        // User data to store
14        String userKey = "user:1";
15        String userData = "{\"email\": \"user1@example.com\"}";
16
17        // Add user data with expiration time of 1 day
18        syncCommands.setex(userKey, Duration.ofDays(1).getSeconds(), userData);
19
20        // Retrieve user data
21        String retrievedData = syncCommands.get(userKey);
22        System.out.println(retrievedData);
23
24        // Close the connection
25        connection.close();
26        redisClient.shutdown();
27    }
28}

Here, we've introduced the setex method to store the user data along with a specified expiration period of one day. Redis manages expiration internally by maintaining a timestamp for when a key is supposed to expire. When the expiration time is reached, the key is automatically deleted from the database.

The get method helps to retrieve the user information we stored earlier.

Now that you have this Java-based template, let's move to the practice section where you can implement and experiment with this logic, enhancing your command over data management in Redis using Lettuce.