Redis - Java

Redis with Modern Java

To use Redis in a modern Java application, you should use a dependency manager like Maven or Gradle to handle the Redis client library. The most popular client is Jedis, but others like Lettuce are also excellent choices, especially for asynchronous and reactive applications. This guide will focus on Jedis.

1. Project Setup with Maven or Gradle

Forget manual JAR downloads. Add the Jedis dependency to your project’s build file.

Maven (pom.xml)

<dependencies>
    <dependency>
        <groupId>redis.clients</groupId>
        <artifactId>jedis</artifactId>
        <version>5.1.0</version> <!-- Check for the latest version -->
    </dependency>
</dependencies>

Gradle (build.gradle.kts)

dependencies {
    implementation("redis.clients:jedis:5.1.0") // Check for the latest version
}

2. Best Practice: Using a Connection Pool

Creating a new connection for every Redis command is inefficient and slow. In a real application, you should use a connection pool, like JedisPool, to manage and reuse connections. It’s thread-safe and should be created once and shared throughout your application.

import redis.clients.jedis.Jedis;
import redis.clients.jedis.JedisPool;
import redis.clients.jedis.JedisPoolConfig;
import redis.clients.jedis.exceptions.JedisException;

public class RedisConnector {
    // Create a singleton instance of the pool
    private static final JedisPool jedisPool = new JedisPool(new JedisPoolConfig(), "localhost", 6379);

    public static void main(String[] args) {
        // Get a resource from the pool and use try-with-resources to ensure it's returned
        try (Jedis jedis = jedisPool.getResource()) {
            // Check connection
            System.out.println("Connection to server successful.");
            System.out.println("Server is running: " + jedis.ping());
        } catch (JedisException e) {
            System.err.println("Failed to connect to Redis: " + e.getMessage());
            e.printStackTrace();
        }

        // Remember to close the pool when your application shuts down
        jedisPool.close();
    }
}

Compile and run this code. Your IDE or build tool will handle the dependencies for you. The output should be:

Connection to server successful.
Server is running: PONG

3. Code Examples

All examples below assume you have a JedisPool configured and use the try-with-resources pattern for safe connection handling.

String Example

try (Jedis jedis = jedisPool.getResource()) {
    String key = "tutorial-name";
    String value = "Modern Redis Tutorial";

    jedis.set(key, value);
    System.out.println("Set key '" + key + "' to '" + value + "'");

    String storedValue = jedis.get(key);
    System.out.println("Retrieved value: " + storedValue);
} catch (JedisException e) {
    System.err.println("Redis operation failed: " + e.getMessage());
}

List Example

import java.util.List;

// ... inside a method with a JedisPool
try (Jedis jedis = jedisPool.getResource()) {
    String listKey = "tech-stack";

    // Clear old list items before running example
    jedis.del(listKey);

    // Add items to the left of the list
    jedis.lpush(listKey, "Java", "Docker", "Redis");

    // Get all items from the list
    List<String> stack = jedis.lrange(listKey, 0, -1);
    System.out.println("Current tech stack: " + stack);
} catch (JedisException e) {
    System.err.println("Redis operation failed: " + e.getMessage());
}

Keys Example (Using SCAN)

Warning: Never use the KEYS * command in a production environment. It is a blocking operation that can freeze your Redis server while it scans all keys. The safe and recommended alternative is SCAN.

import redis.clients.jedis.params.ScanParams;
import redis.clients.jedis.resps.ScanResult;
import java.util.ArrayList;
import java.util.List;

// ... inside a method with a JedisPool
try (Jedis jedis = jedisPool.getResource()) {
    System.out.println("\nScanning for keys with pattern 'tutorial-*: '");
    ScanParams scanParams = new ScanParams().match("tutorial-*").count(100);
    String cursor = ScanParams.SCAN_POINTER_START;
    List<String> matchingKeys = new ArrayList<>();

    do {
        ScanResult<String> scanResult = jedis.scan(cursor, scanParams);
        matchingKeys.addAll(scanResult.getResult());
        cursor = scanResult.getCursor();
    } while (!cursor.equals(ScanParams.SCAN_POINTER_START));

    if (matchingKeys.isEmpty()) {
        System.out.println("No matching keys found.");
    } else {
        System.out.println("Found keys: " + matchingKeys);
    }
} catch (JedisException e) {
    System.err.println("Redis operation failed: " + e.getMessage());
}

Further Learning

For enterprise applications, consider using a framework abstraction like Spring Data Redis, which simplifies connection management, object mapping, and provides template classes for easier Redis interaction.