RedisTemplate

Introduction

RedisTemplate is the central Spring API — opsForValue, opsForHash, opsForZSet wrap Redis commands with serialization hooks. Every production bug from garbled cache values traces to serializer mismatch between writer and reader services.

Operations are synchronous by default on Lettuce; use RedisCallback for low-level access. executeSession for WATCH/MULTI transactions.

Namespace templates by domain bean — productRedisTemplate vs sessionRedisTemplate — to enforce serializer boundaries.

Understanding the topic

Key concepts

• opsForValue() — string commands.
• opsForHash() — hash commands.
• opsForZSet(), opsForList(), opsForSet().
• opsForStream() — stream commands Redis 5+.
• Serializers on key, value, hash field.
• execute(RedisCallback) low-level.

flowchart LR
  Controller --> Service
  Service --> RedisTemplate
  RedisTemplate --> Redis

Step-by-step explanation

1. Template serializes key/value to bytes.
2. Sends command via connection factory.
3. Deserializes reply to Java type.
4. Connection returned to pool.
5. Exceptions wrapped in DataAccessException.

Syntax reference

Common commands

• Duration TTL overload on set.
• BoundKeyOperations for fixed key prefix.
• DefaultRedisSerializer is JDK — override.

redis.opsForValue().set("k", "v", Duration.ofMinutes(10));
redis.opsForHash().put("h", "field", "val");
redis.opsForZSet().add("z", "member", 1.0);
redis.delete("k");

Informative example

Domain-specific template with JSON values and key prefix helper:

@Service
public class CatalogCache {
    private final RedisTemplate<String, Product> redis;

    public CatalogCache(RedisTemplate<String, Product> redis) { this.redis = redis; }

    public void put(String sku, Product p) {
        redis.opsForValue().set("catalog:" + sku, p, Duration.ofHours(1));
    }

    public Optional<Product> get(String sku) {
        return Optional.ofNullable(redis.opsForValue().get("catalog:" + sku));
    }
}

Java 21 · Spring Boot 3 · inject typed template bean from RedisConfig.

Real-world use

Real-world use cases

• Cache CRUD in service layer.
• Session hash via opsForHash.
• Leaderboard via opsForZSet.
• Distributed lock via opsForValue setIfAbsent.
• Stream consumer via opsForStream.

Best practices

• Dedicated template beans per value type.
• StringRedisTemplate for plain JSON strings.
• Consistent key prefix constants class.
• Use Duration TTL overloads not raw seconds.
• executePipelined for batch paths.
• Log serializer config at startup in debug.

Common mistakes

• Service A writes JSON string Service B reads with JDK serializer.
• Sharing one template with mixed value types.
• Ignoring null returns from get.
• Blocking opsForStream in HTTP thread without timeout.

Advanced interview questions

Summary

RedisTemplate = typed Redis command facade.