How to cache data during application startup in Spring boot application

Question

I have a Spring boot Application connecting to SQL Server Database. I need some help in using caching in my application. I have a table for CodeCategory which has a list of codes for Many codes. This table will be loaded every month and data changes only once in a month. I want to cache this entire table when the Application starts. In any subsequent calls to the table should get value from this cache instead of calling the Database.

For Example,

List<CodeCategory> findAll();

I want to cache the above DB query value during application startup. If there is a DB call like List<CodeCategory> findByCodeValue(String code) should fetch the code result from the already Cached data instead of calling the Database.

Please let me know how this can be achieved using spring boot and ehcache.

Answer 1

As pointed out, It takes some time for ehcache to setup and it is not working completely with @PostConstruct. In that case make use of ApplicationStartedEvent to load the cache.

GitHub Repo: spring-ehcache-demo

@Service
class CodeCategoryService{

   @EventListener(classes = ApplicationStartedEvent.class )
   public void listenToStart(ApplicationStartedEvent event) {
        this.repo.findByCodeValue("100");
   }

}

interface CodeCategoryRepository extends JpaRepository<CodeCategory, Long>{

    @Cacheable(value = "codeValues")
    List<CodeCategory> findByCodeValue(String code);
}

Note: There are multiple ways as pointed by others. You can choose as per your needs.

Answer 2

My way is to define a generic cache handler

@FunctionalInterface
public interface GenericCacheHandler {

List<CodeCategory> findAll();
 }

And its implementation as below

@Component
@EnableScheduling  // Important
public class GenericCacheHandlerImpl implements GenericCacheHandler {

@Autowired
private CodeRepository codeRepo;

private List<CodeCategory> codes = new ArrayList<>();

@PostConstruct
private void intializeBudgetState() {
    List<CodeCategory> codeList = codeRepo.findAll();
    // Any customization goes here
    codes = codeList;
}

@Override
public List<CodeCategory> getCodes() {
    return codes;
}
}

Call it in Service layer as below

@Service
public class CodeServiceImpl implements CodeService {

@Autowired
private GenericCacheHandler genericCacheHandler;

@Override
public CodeDTO anyMethod() {
    return genericCacheHandler.getCodes();
}   
}