How to implement caching of reference books from a database in a Java application considering multithreading?

To cache reference data from a database in a Java application considering multithreading, the following approaches can be used:

1. Using thread-safe collections — for example, ConcurrentHashMap for cache storage.

2. Initializing the cache at application startup or lazy loading using double-checked locking to avoid simultaneous data loading by multiple threads.

3. Updating the cache can be implemented through periodic reloads (for example, using ScheduledExecutorService) or based on events.

4. Using ready-made cache libraries — such as Caffeine or Guava Cache, which already provide thread safety and convenient update mechanisms.

An example of a simple cache with ConcurrentHashMap and lazy loading:

import java.util.concurrent.*;

public class ReferenceCache {
    private final ConcurrentHashMap<String, String> cache = new ConcurrentHashMap<>();

    public String getValue(String key) {
        return cache.computeIfAbsent(key, k -> loadFromDb(k));
    }

    private String loadFromDb(String key) {
        // Simulate loading from DB
        return "Value for " + key;
    }

    // Method for periodic cache update
    public void refreshCache() {
        // Logic for updating, e.g., loading all data and replacing cache content
    }
}

This approach guarantees that when multiple threads request the same key simultaneously, the database load occurs only once, and other threads will receive the result from the cache.