Spring缓存

Spring中的缓存抽象

Spring Cache 是 Spring 提供的一整套的缓存解决方案。虽然它本身并没有提供缓存的实现，但是它提供了一整套的接口和代码规范、配置、注解等，这样它就可以整合各种缓存方案了，比如 Redis、Ehcache，我们也就不用关心操作缓存的细节。

Spring 3.1 开始定义了 org.springframework.cache.Cache 和 org.springframework.cache.CacheManager 接口来统一不同的缓存技术，并支持使用注解来简化我们开发。

Cache 接口它包含了缓存的各种操作方式，同时还提供了各种xxxCache缓存的实现，比如 RedisCache 针对Redis，EhCacheCache 针对 EhCache，ConcurrentMapCache 针对 ConcurrentMap

Spring Cache 常用注解

Spring提供了四个注解来声明缓存规则：@Cacheable，@CachePut，@CacheEvict，@Caching

SpringEL上下文对象

源码解析

首先看下EnableCaching注解，引入了CachingConfigurationSelector配置类

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(CachingConfigurationSelector.class)
public @interface EnableCaching {

	/**
	 * Indicate whether subclass-based (CGLIB) proxies are to be created as opposed
	 * to standard Java interface-based proxies. The default is {@code false}. <strong>
	 * Applicable only if {@link #mode()} is set to {@link AdviceMode#PROXY}</strong>.
	 * <p>Note that setting this attribute to {@code true} will affect <em>all</em>
	 * Spring-managed beans requiring proxying, not just those marked with {@code @Cacheable}.
	 * For example, other beans marked with Spring's {@code @Transactional} annotation will
	 * be upgraded to subclass proxying at the same time. This approach has no negative
	 * impact in practice unless one is explicitly expecting one type of proxy vs another,
	 * e.g. in tests.
	 */
	boolean proxyTargetClass() default false;

	/**
	 * Indicate how caching advice should be applied.
	 * <p><b>The default is {@link AdviceMode#PROXY}.</b>
	 * Please note that proxy mode allows for interception of calls through the proxy
	 * only. Local calls within the same class cannot get intercepted that way;
	 * a caching annotation on such a method within a local call will be ignored
	 * since Spring's interceptor does not even kick in for such a runtime scenario.
	 * For a more advanced mode of interception, consider switching this to
	 * {@link AdviceMode#ASPECTJ}.
	 */
	AdviceMode mode() default AdviceMode.PROXY;

	/**
	 * Indicate the ordering of the execution of the caching advisor
	 * when multiple advices are applied at a specific joinpoint.
	 * <p>The default is {@link Ordered#LOWEST_PRECEDENCE}.
	 */
	int order() default Ordered.LOWEST_PRECEDENCE;

}

再看下CachingConfigurationSelector类，默认为PROXY模式，会加载AutoProxyRegistrar和ProxyCachingConfiguration两个配置。

public class CachingConfigurationSelector extends AdviceModeImportSelector<EnableCaching> {


	/**
	 * Returns {@link ProxyCachingConfiguration} or {@code AspectJCachingConfiguration}
	 * for {@code PROXY} and {@code ASPECTJ} values of {@link EnableCaching#mode()},
	 * respectively. Potentially includes corresponding JCache configuration as well.
	 */
	@Override
	public String[] selectImports(AdviceMode adviceMode) {
		switch (adviceMode) {
			case PROXY:
				return getProxyImports();
			case ASPECTJ:
				return getAspectJImports();
			default:
				return null;
		}
	}

	/**
	 * Return the imports to use if the {@link AdviceMode} is set to {@link AdviceMode#PROXY}.
	 * <p>Take care of adding the necessary JSR-107 import if it is available.
	 */
	private String[] getProxyImports() {
		List<String> result = new ArrayList<>(3);
		result.add(AutoProxyRegistrar.class.getName());
		result.add(ProxyCachingConfiguration.class.getName());
		if (jsr107Present && jcacheImplPresent) {
			result.add(PROXY_JCACHE_CONFIGURATION_CLASS);
		}
		return StringUtils.toStringArray(result);
	}
}

再看看ProxyCachingConfiguration类中，发现这个类定义了缓存的拦截器

	@Bean
	@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
	public CacheInterceptor cacheInterceptor(CacheOperationSource cacheOperationSource) {
		CacheInterceptor interceptor = new CacheInterceptor();
		interceptor.configure(this.errorHandler, this.keyGenerator, this.cacheResolver, this.cacheManager);
		interceptor.setCacheOperationSource(cacheOperationSource);
		return interceptor;
	}

在父类AbstractCachingConfiguration中还处理了用户自定义的缓存属性

	@Autowired
	void setConfigurers(ObjectProvider<CachingConfigurer> configurers) {
		Supplier<CachingConfigurer> configurer = () -> {
			List<CachingConfigurer> candidates = configurers.stream().collect(Collectors.toList());
			if (CollectionUtils.isEmpty(candidates)) {
				return null;
			}
			if (candidates.size() > 1) {
				throw new IllegalStateException(candidates.size() + " implementations of " +
						"CachingConfigurer were found when only 1 was expected. " +
						"Refactor the configuration such that CachingConfigurer is " +
						"implemented only once or not at all.");
			}
			return candidates.get(0);
		};
		useCachingConfigurer(new CachingConfigurerSupplier(configurer));
	}

	/**
	 * Extract the configuration from the nominated {@link CachingConfigurer}.
	 */
	protected void useCachingConfigurer(CachingConfigurerSupplier cachingConfigurerSupplier) {
		this.cacheManager = cachingConfigurerSupplier.adapt(CachingConfigurer::cacheManager);
		this.cacheResolver = cachingConfigurerSupplier.adapt(CachingConfigurer::cacheResolver);
		this.keyGenerator = cachingConfigurerSupplier.adapt(CachingConfigurer::keyGenerator);
		this.errorHandler = cachingConfigurerSupplier.adapt(CachingConfigurer::errorHandler);
	}