How to load @Cache on startup in spring?

Question

I'm using spring-cache to improve database queries, which works fine as follows:

@Bean
public CacheManager cacheManager() {
    return new ConcurrentMapCacheManager("books");
}

@Cacheable("books")
public Book getByIsbn(String isbn) {
    return dao.findByIsbn(isbn);
}

But now I want to prepopulate the full book-cache on startup. Which means I want to call dao.findAll() and put all values into the cache. This routine shall than only be scheduled periodically.

But how can I explicit populate a cache when using @Cacheable?

Answer 1

Just use the cache as before, add a scheduler to update cache, code snippet is below.

@Service
public class CacheScheduler {
    @Autowired
    BookDao bookDao;
    @Autowired
    CacheManager cacheManager;

    @PostConstruct
    public void init() {
        update();
        scheduleUpdateAsync();
    }

    public void update() {
        for (Book book : bookDao.findAll()) {
            cacheManager.getCache("books").put(book.getIsbn(), book);
        }
    }
}

Make sure your KeyGenerator will return the object for one parameter (as default). Or else, expose the putToCache method in BookService to avoid using cacheManager directly.

@CachePut(value = "books", key = "#book.isbn")
public Book putToCache(Book book) {
    return book;
}

Answer 2

I have encountered the following problem when using @PostConstruct: - even though the method I wanted to be cached was called, after calling it from swagger, it still didn't use the cached value. Only after called it once more.

That was because @PostConstruct is too early for caching something. (At least I think that was the issue)

Now I'm using it more late in the startup process and it works without problems:

@Component
public class CacheInit implements ApplicationListener<ApplicationReadyEvent> {

    @Override
    public void onApplicationEvent(ApplicationReadyEvent event) {
       //call service method
    }

}