# Lettuce — Scalable Async Redis Client for Java

> Lettuce is a thread-safe, non-blocking Redis client for Java built on Netty, supporting synchronous, asynchronous, and reactive programming models with full Redis Cluster and Sentinel support.

## Install

Save in your project root:

# Lettuce — Scalable Async Redis Client for Java

## Quick Use
```xml
<dependency>
  <groupId>io.lettuce</groupId>
  <artifactId>lettuce-core</artifactId>
  <version>6.4.0.RELEASE</version>
</dependency>
```
```java
RedisClient client = RedisClient.create("redis://localhost:6379");
StatefulRedisConnection<String, String> conn = client.connect();
RedisCommands<String, String> sync = conn.sync();
sync.set("key", "value");
String val = sync.get("key");
conn.close();
client.shutdown();
```

## Introduction
Lettuce is an advanced Java client for Redis built on top of Netty. Unlike Jedis, Lettuce uses non-blocking I/O, making a single connection safely shareable across multiple threads. It is the default Redis driver in Spring Data Redis and supports synchronous, asynchronous (CompletableFuture), and reactive (Project Reactor) APIs.

## What Lettuce Does
- Provides synchronous, asynchronous, and reactive APIs for all Redis commands
- Shares a single connection safely across threads via non-blocking Netty I/O
- Supports Redis Cluster with automatic topology refresh and adaptive routing
- Handles Redis Sentinel for automatic master discovery and failover
- Offers client-side caching and connection pooling for high-throughput use cases

## Architecture Overview
Lettuce uses Netty's event loop for network I/O, multiplexing commands over a single TCP connection. Commands are encoded into RESP protocol frames and queued; responses are demultiplexed and dispatched to the correct future or subscriber. For Redis Cluster, Lettuce maintains a topology map and routes commands by hash slot. The reactive API wraps responses in Project Reactor Mono and Flux types.

## Self-Hosting & Configuration
- Add lettuce-core as a Maven or Gradle dependency
- Create a RedisClient with a Redis URI including host, port, and optional password
- For Cluster, use RedisClusterClient with seed node URIs
- Configure connection timeout, auto-reconnect, and topology refresh intervals via ClientOptions
- For reactive usage, add Project Reactor to your classpath

## Key Features
- Non-blocking I/O with a single thread-safe connection per client
- Three programming models: sync, async (CompletableFuture), and reactive (Reactor)
- Automatic Redis Cluster topology refresh with periodic and adaptive triggers
- TLS/SSL support for encrypted connections to Redis
- Client-side caching with server-assisted invalidation (Redis 6+ tracking)

## Comparison with Similar Tools
- **Jedis** — synchronous and simpler; Lettuce is non-blocking and thread-safe by default
- **Redisson** — higher-level distributed objects; Lettuce is a lower-level driver
- **Spring Data Redis** — abstraction layer that uses Lettuce as its default driver
- **ioredis (Node.js)** — similar async-first philosophy for the JavaScript ecosystem
- **redis-rs (Rust)** — async Redis client for Rust with comparable design goals

## FAQ
**Q: When should I choose Lettuce over Jedis?**
A: Use Lettuce when you need async or reactive APIs, thread-safe shared connections, or Redis Cluster with automatic topology updates.

**Q: Does Lettuce support connection pooling?**
A: Lettuce connections are thread-safe, so pooling is often unnecessary. For high-throughput scenarios, Lettuce provides an optional connection pool via AsyncPool.

**Q: Is Lettuce compatible with Valkey?**
A: Yes. Lettuce communicates via the RESP protocol and works with Valkey, KeyDB, DragonflyDB, and other Redis-compatible servers.

**Q: How does Lettuce handle Redis Cluster failover?**
A: Lettuce periodically refreshes the cluster topology and supports adaptive refresh triggered by MOVED/ASK redirections, automatically routing to new primaries.

## Sources
- https://github.com/lettuce-io/lettuce-core
- https://lettuce.io/core/release/reference/

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Source: https://tokrepo.com/en/workflows/asset-80031eef
Author: AI Open Source