What approaches do you use to optimize request processing speed?

To optimize query processing speed in Java applications, several approaches can be used:

1. Caching — storing results of frequently requested data in memory for quick access.
2. Asynchronous processing — using multithreading or non-blocking I/O to increase throughput.
3. Database query optimization — indexes, reducing the number of queries, using efficient queries.
4. Thread pool — managing the number of requests processed simultaneously.
5. Profiling and monitoring — identifying bottlenecks and eliminating them.

Example of using caching with Spring Cache:

@Service
public class UserService {
    @Cacheable("users")
    public User getUserById(Long id) {
        // Expensive operation, e.g., database query
        return userRepository.findById(id).orElse(null);
    }
}

This approach reduces load and speeds up repeated requests.