@CacheEvict

The @CacheEvict is used to trigger explicit cache eviction. By default most of caching frameworks expires the cache data after some defined duration. The @CacheEvict annotation is useful when you want to control explicit cache eviction upon some method calls. It is useful for removing stale or unused data from the underlying cache.

One of the notable features of @CacheEvict is that it can be used with void methods and as a result these methods tend to act as triggers and the return values are ignored. This is not the case with @Cacheable which adds/update data into the cache and thus requires a result.

The various properties of the @CacheEvict annotation are summarized as shown in Table 10-2 below.

Table 10-2. @CacheEvict settings details

In Listing 10-12, after saving the customer, evict the customers from the underlying cache so that the customer list is updated and kept in the cache at all times.

Listing 10-12. Usage of @CacheEvict annotation

[java]public class CustomerRepository{

@CacheEvict(value=“customer”, allEntries=true)

public Customer saveCustomer(String customerCode){

//….After saving customer, evict the map holding the cutsomers….

}

}[/java]

@CachePut

The @CachePut annotation allows you to “update” a cache entry without interfering with the method execution. This is very similar to @Cacheable but for entry update. The @CachePut annotation has exactly the same attributes as @Cacheable.

Using @CachePut and @Cacheable annotations on the same method is generally discouraged because they have different behaviors. @Cacheable annotation causes the method execution to be skipped by using the cache and @CachePut annotation forces the execution in order to execute a cache update. This could result in unexpected behaviors and could also result in exceptions.

In the case of @CachePut, shown in Listing 10-13, the method is always executed and its returned result is put into the cache, using the provided key generator and replaces the old entry as the case may be. The only case where the method is not executed is when you provide an optional @CachePut condition and the condition is not met.

Listing 10-13. Usage of @CachePut annotation

[java]public class CustomerRepository{

@CachePut(value=“customer”)

public Customer updateCustomer(String customerCode){

//….After saving customer, update the customers map

}

}[/java]

@Caching

It is a group annotation for multiple cache annotation explained in the above sections. It groups @Cacheable, @CacheEvict and @CachePut annotation into a single annotation. This can be called as a sort of stereotype annotation. The various properties of the @Caching annotation are summarized as shown in Table 10-3 below.

Table 10-3. @Caching settings details

Listing 10-14. Complete class showing the usage of  various cache related annotations

[java]import org.springframework.cache.annotation.CacheEvict;

import org.springframework.cache.annotation.Cacheable;

import org.springframework.stereotype.Repository;

@Repository

public class JdbcCustomerRepository implements CustomerRepository {

//…….

private final Map<string, customer=""> customers =

new ConcurrentHashMap<string, customer="">();

JdbcCustomerRepository(Map<string, customer=""> customers){

this.customers = customers;

}

@Cacheable("customer")

public Customer getCustomer(String customerCode){

return customers.get(customerCode);

}

@CacheEvict(value="customer", key="customer.customerCode")

public void saveCustomer(Customer customer){

customers.put(customer.getCustomerCode(), customer);

}

public Collection getAllCustomers() {

return customers.values();

}

//…….

}[/java]

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Tomcy John

Blogger & Author at javacodebook

He is an Enterprise Java Specialist holding a degree in Engineering (B-Tech) with over 10 years of experience in several industries. He's currently working as Principal Architect at Emirates Group IT since 2005. Prior to this he has worked with Oracle Corporation and Ernst & Young. His main specialization is on various web technologies and acts as chief mentor and Architect to facilitate incorporating Spring as Corporate Standard in the organization.

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