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31. Caching
The Spring Framework provides support for transparently adding caching to an application. At its core, the abstraction applies caching to methods, reducing thus the number of executions based on the information available in the cache. The caching logic is applied transparently, without any interference to the invoker. Spring Boot auto-configures the cache infrastructure as long as the caching support is enabled via the @EnableCaching
annotation.
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Check the relevant section of the Spring Framework reference for more details. |
In a nutshell, adding caching to an operation of your service is as easy as adding the relevant annotation to its method:
import org.springframework.cache.annotation.Cacheable
import org.springframework.stereotype.Component;
@Component
public class MathService {
@Cacheable("piDecimals")
public int computePiDecimal(int i) {
// ...
}
}
This example demonstrates the use of caching on a potentially costly operation. Before invoking computePiDecimal
, the abstraction will look for an entry in the piDecimals
cache matching the i
argument. If an entry is found, the content in the cache is immediately returned to the caller and the method is not invoked. Otherwise, the method is invoked and the cache is updated before returning the value.
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You can also use the standard JSR-107 (JCache) annotations (e.g. |
If you do not add any specific cache library, Spring Boot will auto-configure a Simple provider that uses concurrent maps in memory. When a cache is required (i.e. piDecimals
in the example above), this provider will create it on-the-fly for you. The simple provider is not really recommended for production usage, but it’s great for getting started and making sure that you understand the features. When you have made up your mind about the cache provider to use, please make sure to read its documentation to figure out how to configure the caches that your application uses. Practically all providers require you to explicitly configure every cache that you use in the application. Some offer a way to customize the default caches defined by the spring.cache.cache-names
property.
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If you are using the cache infrastructure with beans that are not interface-based, make sure to enable the |
The cache abstraction does not provide an actual store and relies on abstraction materialized by the org.springframework.cache.Cache
and org.springframework.cache.CacheManager
interfaces.
If you haven’t defined a bean of type CacheManager
or a CacheResolver
named cacheResolver
(see CachingConfigurer
), Spring Boot tries to detect the following providers (in this order):
- Generic
- JCache (JSR-107) (EhCache 3, Hazelcast, Infinispan, etc)
- EhCache 2.x
- Hazelcast
- Infinispan
- Couchbase
- Redis
- Caffeine
- Guava (deprecated)
- Simple
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It is also possible to force the cache provider to use via the |
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Use the |
If the CacheManager
is auto-configured by Spring Boot, you can further tune its configuration before it is fully initialized by exposing a bean implementing the CacheManagerCustomizer
interface. The following sets a flag to say that null values should be passed down to the underlying map.
@Bean
public CacheManagerCustomizer<ConcurrentMapCacheManager> cacheManagerCustomizer() {
return new CacheManagerCustomizer<ConcurrentMapCacheManager>() {
@Override
public void customize(ConcurrentMapCacheManager cacheManager) {
cacheManager.setAllowNullValues(false);
}
};
}
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In the example above, an auto-configured |
Generic caching is used if the context defines at least one org.springframework.cache.Cache
bean. A CacheManager
wrapping all beans of that type is created.
JCache is bootstrapped via the presence of a javax.cache.spi.CachingProvider
on the classpath (i.e. a JSR-107 compliant caching library) and the JCacheCacheManager
provided by the spring-boot-starter-cache
‘Starter’. There are various compliant libraries out there and Spring Boot provides dependency management for Ehcache 3, Hazelcast and Infinispan. Any other compliant library can be added as well.
It might happen that more than one provider is present, in which case the provider must be explicitly specified. Even if the JSR-107 standard does not enforce a standardized way to define the location of the configuration file, Spring Boot does its best to accommodate with implementation details.
# Only necessary if more than one provider is present
spring.cache.jcache.provider=com.acme.MyCachingProvider
spring.cache.jcache.config=classpath:acme.xml
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Since a cache library may offer both a native implementation and JSR-107 support Spring Boot will prefer the JSR-107 support so that the same features are available if you switch to a different JSR-107 implementation. |
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Spring Boot has a general support for Hazelcast. If a single |
There are several ways to customize the underlying javax.cache.cacheManager
:
- Caches can be created on startup via the
spring.cache.cache-names
property. If a customjavax.cache.configuration.Configuration
bean is defined, it is used to customize them. org.springframework.boot.autoconfigure.cache.JCacheManagerCustomizer
beans are invoked with the reference of theCacheManager
for full customization.
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If a standard |
EhCache 2.x is used if a file named ehcache.xml
can be found at the root of the classpath. If EhCache 2.x, the EhCacheCacheManager
provided by the spring-boot-starter-cache
‘Starter’ and such file is present it is used to bootstrap the cache manager. An alternate configuration file can be provided as well using:
spring.cache.ehcache.config=classpath:config/another-config.xml
Spring Boot has a general support for Hazelcast. If a HazelcastInstance
has been auto-configured, it is automatically wrapped in a CacheManager
.
Infinispan has no default configuration file location so it must be specified explicitly (or the default bootstrap is used).
spring.cache.infinispan.config=infinispan.xml
Caches can be created on startup via the spring.cache.cache-names
property. If a custom ConfigurationBuilder
bean is defined, it is used to customize them.
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The support of Infinispan in Spring Boot is restricted to the embedded mode and is quite basic. If you want more options you should use the official Infinispan Spring Boot starter instead, check the documentation for more details. |
If the Couchbase java client and the couchbase-spring-cache
implementation are available and Couchbase is configured, a CouchbaseCacheManager
will be auto-configured. It is also possible to create additional caches on startup using the spring.cache.cache-names
property. These will operate on the Bucket
that was auto-configured. You can also create additional caches on another Bucket
using the customizer: assume you need two caches on the "main" Bucket
(foo
and bar
) and one biz
cache with a custom time to live of 2sec on the another
Bucket
. First, you can create the two first caches simply via configuration:
spring.cache.cache-names=foo,bar
Then define this extra @Configuration
to configure the extra Bucket
and the biz
cache:
@Configuration
public class CouchbaseCacheConfiguration {
private final Cluster cluster;
public CouchbaseCacheConfiguration(Cluster cluster) {
this.cluster = cluster;
}
@Bean
public Bucket anotherBucket() {
return this.cluster.openBucket("another", "secret");
}
@Bean
public CacheManagerCustomizer<CouchbaseCacheManager> cacheManagerCustomizer() {
return c -> {
c.prepareCache("biz", CacheBuilder.newInstance(anotherBucket())
.withExpiration(2));
};
}
}
This sample configuration reuses the Cluster
that was created via auto-configuration.
If Redis is available and configured, the RedisCacheManager
is auto-configured. It is also possible to create additional caches on startup using the spring.cache.cache-names
property.
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By default, a key prefix is added to prevent that if two separate caches use the same key, Redis would have overlapping keys and be likely to return invalid values. We strongly recommend to keep this setting enabled if you create your own |
Caffeine is a Java 8 rewrite of Guava’s cache and will supersede the Guava support in Spring Boot 2.0. If Caffeine is present, a CaffeineCacheManager
(provided by the spring-boot-starter-cache
‘Starter’) is auto-configured. Caches can be created on startup using the spring.cache.cache-names
property and customized by one of the following (in this order):
- A cache spec defined by
spring.cache.caffeine.spec
- A
com.github.benmanes.caffeine.cache.CaffeineSpec
bean is defined - A
com.github.benmanes.caffeine.cache.Caffeine
bean is defined
For instance, the following configuration creates a foo
and bar
caches with a maximum size of 500 and a time to live of 10 minutes
spring.cache.cache-names=foo,bar
spring.cache.caffeine.spec=maximumSize=500,expireAfterAccess=600s
Besides, if a com.github.benmanes.caffeine.cache.CacheLoader
bean is defined, it is automatically associated to the CaffeineCacheManager
. Since the CacheLoader
is going to be associated to all caches managed by the cache manager, it must be defined as CacheLoader<Object, Object>
. Any other generic type will be ignored by the auto-configuration.
If Guava is present, a GuavaCacheManager
is auto-configured. Caches can be created on startup using the spring.cache.cache-names
property and customized by one of the following (in this order):
- A cache spec defined by
spring.cache.guava.spec
- A
com.google.common.cache.CacheBuilderSpec
bean is defined - A
com.google.common.cache.CacheBuilder
bean is defined
For instance, the following configuration creates a foo
and bar
caches with a maximum size of 500 and a time to live of 10 minutes
spring.cache.cache-names=foo,bar
spring.cache.guava.spec=maximumSize=500,expireAfterAccess=600s
Besides, if a com.google.common.cache.CacheLoader
bean is defined, it is automatically associated to the GuavaCacheManager
. Since the CacheLoader
is going to be associated to all caches managed by the cache manager, it must be defined as CacheLoader<Object, Object>
. Any other generic type will be ignored by the auto-configuration.
If none of the other providers can be found, a simple implementation using a ConcurrentHashMap
as cache store is configured. This is the default if no caching library is present in your application. Caches are created on-the-fly by default but you can restrict the list of available caches using the cache-names
property. For instance, if you want only foo
and bar
caches:
spring.cache.cache-names=foo,bar
If you do this and your application uses a cache not listed then it will fail at runtime when the cache is needed, but not on startup. This is similar to the way the "real" cache providers behave if you use an undeclared cache.