Cache in Spring

Use cache in spring, need following steps:

Enable Cache

@Configuration
@EnableCaching
public class CachingConfig {
  @Bean
  public CacheManager cacheManager() {
    return new ConcurrentMapCacheManager("categoryOrders");
  }
}

The "categoryOrders" is a cache name. The ConcurrentMapCacheManager can accept multiple caches.

Bind Annotation on Method

There are several annotations:

• @Cacheable
  The simplest way to enable caching behavior for a method is to demarcate it with @Cacheable and parameterize it with the name of the cache where the results would be stored:

  @Cacheable("categoryOrders")
   List<Order> findAllOrders() {
    return findAll();
  }

The first time the application will get all orders from database and cache it in "categoryOrders"

• @CacheEvict
  When the data of category has been changed, we want to clean the cache. So we can bind this annotation on the method to clean the cache.

  @CacheEvict(value = "categoryOrders", allEntries = true)
  public void cleanCategoryOrderCache() {
  }

allEntries = true means clean all data.

• @CachePut
@CacheEvict annotation is clean all data. Sometimes, you only need to update a fraction of data. You can use @CachePut annotation.

@CachePut(value="categoryOrders")
public Order getOrder(String orderId) {...}

The difference between @CachePut and @Cacheable is that @CachePut
will invoke the method every time, but @Cacheable will invoke this method at first time.
We can also add condition in those annotations, such as:

@CachePut(value="categoryOrders", condition="#order.type==1")
public Order getOrder(String orderId) {...}

@CachePut(value="categoryOrders", unless="#order.type==3")
public Order getOrder(String orderId) {...}

There are many parameters you can define in each annotation.
The thing you need pay attention is that the theory of spring cache is AOP. So when you call the cache method in the same class, the cache will not be work. such as:

public class CategoryOrderGenerator {
  private CategoryOrderRepository categoryOrderRepository;

  @Autowired
  public CategoryOrderGenerator(CategoryOrderRepository categoryOrderRepository) {
    this.categoryOrderRepository = categoryOrderRepository;
  }

  public List<CategoryOrder> getCategoryOrder(List<String> parameters)
    return categoryOrderRepository.findAllCategoryOrders().stream()
        .filter(....)
        .map(....)
        .collect(Collectors.toList());
  }

  @Cacheable("categoryOrders")
  public List<CategoryOrder> getAll() {
    return categoryOrderRepository.findAllCategoryOrders();
  }
}

The "getCategoryOrder" method and cached "getAll()" are in same class. The "getCategoryOrder" call the "getAll()" method. So the cache will not work, because this two method are in same class. You can add the @Cacheable("categoryOrders") to findAllCategoryOrders() method in repository.