Java注解@Cacheable的工作原理

In order to avoid unnecessary query on database it is a common pattern to define a cache in application layer to cache the query result from database. See one example below. Here the application cache is maintained in a custom class CacheContext.

public class AccountService1 {
    private final Logger logger = LoggerFactory.getLogger(AccountService1.class);
    
    private CacheContext<Account> accountCacheContext;
 
    public Account getAccountByName(String accountName) {
        Account result = accountCacheContext.get(accountName);
        if (result != null) {
            logger.info("get from cache... {}", accountName);
            return result;
        }
 
        Optional<Account> accountOptional = getFromDB(accountName);
        if (!accountOptional.isPresent()) {
            throw new IllegalStateException(String.format("can not find account by account name : [%s]", accountName));
        }
 
        Account account = accountOptional.get();
        accountCacheContext.addOrUpdateCache(accountName, account);
        return account;
    }
      

In Spring there is an annotation @Cacheable which can make the cache managed by Spring instead of application developer. See improved version:

public class AccountService2 {
 
    private final Logger logger = LoggerFactory.getLogger(AccountService2.class);

    @Cacheable(value="accountCache")
    public Account getAccountByName(String accountName) {
        logger.info("in method getAccountByName, querying account... {}", accountName);
        Optional<Account> accountOptional = getFromDB(accountName);
        if (!accountOptional.isPresent()) {
            throw new IllegalStateException(String.format("can not find account by account name : [%s]", accountName));
        }
        return accountOptional.get();
    }
      

In this example, there is no more cache evaluation and cache fill logic. All such stuff are taken over by Spring under the hood and completely transparent to application developer, with the help of following bean configuration in xml:

Below is the screenshot for Spring internal cache to store application data, which is based on ConcurrentHashMap. Our cached Account instance with id 2495 could be found there.

For the second query request issued by application, the cached result will be returned by Spring handler:

Here the dynamic proxy is created based on configuration defined in xml with the help of CGlibAopProxy. For more detail about CGlibAopProxy, please refer to Spring official document.