Caching in Spring Boot: In-Memory vs. Redis Distributed Cache.

// Spring Boot Caching Annotations
package com.example.demo.service;

import com.example.demo.model.User;
import com.example.demo.repository.UserRepository;
import org.springframework.cache.annotation.Cacheable;
import org.springframework.cache.annotation.CachePut;
import org.springframework.cache.annotation.CacheEvict;
import org.springframework.stereotype.Service;

@Service
public class UserService {

    private final UserRepository userRepo;

    public UserService(UserRepository userRepo) {
        this.userRepo = userRepo;
    }

    // 1. @Cacheable: If key exists in cache, return it. Otherwise execute DB query and cache result.
    @Cacheable(value = "users", key = "#id")
    public User getUserById(Long id) {
        System.out.println("Fetching from Database for ID: " + id);
        return userRepo.findById(id).orElseThrow();
    }

    // 2. @CachePut: Always executes method and updates cache with fresh data
    @CachePut(value = "users", key = "#user.id")
    public User updateUser(User user) {
        return userRepo.save(user);
    }

    // 3. @CacheEvict: Removes entry from cache on deletion to prevent stale reads
    @CacheEvict(value = "users", key = "#id")
    public void deleteUser(Long id) {
        userRepo.deleteById(id);
    }
}

# application.yml
# Switching from default in-memory cache to distributed Redis
spring:
  cache:
    type: redis
    redis:
      time-to-live: 600000 # 10 minutes TTL
      cache-null-values: false
  data:
    redis:
      host: ${REDIS_HOST:localhost}
      port: 6379
      timeout: 2000ms
      lettuce:
        pool:
          max-active: 16
          max-idle: 8
          min-idle: 2