SpringCache源码解析（一）

一、springCache如何实现自动装配

SpringBoot 确实是通过 spring.factories 文件实现自动配置的。Spring Cache 也是遵循这一机制来实现自动装配的。

具体来说,Spring Cache 的自动装配是通过 org.springframework.boot.autoconfigure.cache.CacheAutoConfiguration 这个类来实现的。这个类位于 spring-boot-autoconfigure 包下。

在 spring-boot-autoconfigure 包的 META-INF/spring.factories 文件中,可以找到 CacheAutoConfiguration 类的配置：
在这里插入图片描述

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.springframework.boot.autoconfigure.cache.CacheAutoConfiguration

二、CacheAutoConfiguration

@Configuration
@ConditionalOnClass(CacheManager.class)
@ConditionalOnBean(CacheAspectSupport.class)
@ConditionalOnMissingBean(value = CacheManager.class, name = "cacheResolver")
@EnableConfigurationProperties(CacheProperties.class)
@AutoConfigureAfter({ CouchbaseAutoConfiguration.class, HazelcastAutoConfiguration.class,HibernateJpaAutoConfiguration.class, RedisAutoConfiguration.class })
@Import(CacheConfigurationImportSelector.class)
public class CacheAutoConfiguration {/*** 创建CacheManagerCustomizers Bean* XxxCacheConfiguration中创建CacheManager时会用来装饰CacheManager*/@Bean@ConditionalOnMissingBeanpublic CacheManagerCustomizers cacheManagerCustomizers(ObjectProvider<CacheManagerCustomizer<?>> customizers) {return new CacheManagerCustomizers(customizers.orderedStream().collect(Collectors.toList()));}/*** 创建CacheManagerValidator Bean* 实现了InitializingBean，在afterPropertiesSet方法中校验CacheManager*/@Beanpublic CacheManagerValidator cacheAutoConfigurationValidator(CacheProperties cacheProperties,ObjectProvider<CacheManager> cacheManager) {return new CacheManagerValidator(cacheProperties, cacheManager);}/*** 后置处理器* 内部类，动态声明EntityManagerFactory实例需要依赖"cacheManager"实例*/@Configuration@ConditionalOnClass(LocalContainerEntityManagerFactoryBean.class)@ConditionalOnBean(AbstractEntityManagerFactoryBean.class)protected static class CacheManagerJpaDependencyConfiguration extends EntityManagerFactoryDependsOnPostProcessor {public CacheManagerJpaDependencyConfiguration() {super("cacheManager");}}/*** 缓存管理器校验器* 内部类，实现了InitializingBean接口，实现afterPropertiesSet用于校验缓存管理器*/static class CacheManagerValidator implements InitializingBean {private final CacheProperties cacheProperties;private final ObjectProvider<CacheManager> cacheManager;CacheManagerValidator(CacheProperties cacheProperties, ObjectProvider<CacheManager> cacheManager) {this.cacheProperties = cacheProperties;this.cacheManager = cacheManager;}/*** 当依赖注入后处理*/@Overridepublic void afterPropertiesSet() {Assert.notNull(this.cacheManager.getIfAvailable(),() -> "No cache manager could " + "be auto-configured, check your configuration (caching "+ "type is '" + this.cacheProperties.getType() + "')");}}/*** 缓存配置导入选择器*/static class CacheConfigurationImportSelector implements ImportSelector {@Overridepublic String[] selectImports(AnnotationMetadata importingClassMetadata) {CacheType[] types = CacheType.values();String[] imports = new String[types.length];for (int i = 0; i < types.length; i++) {imports[i] = CacheConfigurations.getConfigurationClass(types[i]);}return imports;}}}

借助Conditional机制实现自动配置条件：

CacheManager.class在类路径上存在；
CacheAspectSupport实例存在（即CacheInterceptor）；
CacheManager实例不存在，且cacheResolver Bean不存在；
当满足以上要求时，就会触发SpringCache的自动配置逻辑，CacheAutoConfiguration会引入其它的Bean，具体如下：
通过@EnableConfigurationProperties使CacheProperties生效；
借助Import机制导入内部类：CacheConfigurationImportSelector和CacheManagerEntityManagerFactoryDependsOnPostProcessor；
创建了CacheManagerCustomizers、CacheManagerValidator Bean；

2.1 关于的一些疑问

关于@ConditionalOnClass，我有一个疑问：

value值是类名，如果类找不到，会不会编译报错；
——会！那value有什么意义？只要能编译过的，肯定都存在。
——@ConditionalOnClass注解之前一直让我感到困惑，类存不存在，编译器就会体现出来，还要这个注解干嘛？后来想了很久，感觉java语法并不是一定要寄生在idea上，所以语法上限制和工具上限制，这是两码事，理论上就应该彼此都要去做。

@ConditionalOnClass还可以用name属性：

@ConditionalOnClass(name="com.xxx.Component2")

可以看下这篇文章：
SpringBoot中的@ConditionOnClass注解

2.2 CacheProperties

// 接收以"spring.cache"为前缀的配置参数
@ConfigurationProperties(prefix = "spring.cache")
public class CacheProperties {// 缓存实现类型// 未指定，则由环境自动检测，从CacheConfigurations.MAPPINGS自上而下加载XxxCacheConfiguration// 加载成功则检测到缓存实现类型private CacheType type;// 缓存名称集合// 通常，该参数配置了则不再动态创建缓存private List<String> cacheNames = new ArrayList<>();private final Caffeine caffeine = new Caffeine();private final Couchbase couchbase = new Couchbase();private final EhCache ehcache = new EhCache();private final Infinispan infinispan = new Infinispan();private final JCache jcache = new JCache();private final Redis redis = new Redis();// getter and setter.../*** Caffeine的缓存配置参数*/public static class Caffeine {...}/*** Couchbase的缓存配置参数*/public static class Couchbase {...}/*** EhCache的缓存配置参数*/public static class EhCache {...}/*** Infinispan的缓存配置参数*/public static class Infinispan {...}/*** JCache的缓存配置参数*/public static class JCache {...}/*** Redis的缓存配置参数*/public static class Redis {// 过期时间，默认永不过期private Duration timeToLive;// 支持缓存空值标识，默认支持private boolean cacheNullValues = true;// 缓存KEY前缀private String keyPrefix;// 使用缓存KEY前缀标识，默认使用private boolean useKeyPrefix = true;// 启用缓存统计标识private boolean enableStatistics;// getter and setter...}
}

2.3 CacheConfigurationImportSelector

CacheAutoConfiguration的静态内部类，实现了ImportSelector接口的selectImports方法，导入Cache配置类；

/*** 挑选出CacheType对应的配置类*/
@Override
public String[] selectImports(AnnotationMetadata importingClassMetadata) {CacheType[] types = CacheType.values();String[] imports = new String[types.length];// 遍历CacheTypefor (int i = 0; i < types.length; i++) {// 获取CacheType的配置类imports[i] = CacheConfigurations.getConfigurationClass(types[i]);}return imports;
}

CacheConfigurationImportSelector，把所有缓存的配置类拿出来，加入到spring中被加载。

有的开发者可能就会问：
为什么要重载所有的配置类？而不是配置了哪种缓存类型就加载哪种缓存类型？
——这里只是加载所有的配置类，比如Redis，只是加载RedisCacheConfiguration.class配置类，后续会根据条件判断具体加载到哪个配置，如下图：

2.4 CacheConfigurations

维护了CacheType和XxxCacheConfiguration配置类的映射关系；

/*** CacheType和配置类的映射关系集合* 无任何配置条件下，从上而下，默认生效为SimpleCacheConfiguration*/
static {Map<CacheType, String> mappings = new EnumMap<>(CacheType.class);mappings.put(CacheType.GENERIC, GenericCacheConfiguration.class.getName());mappings.put(CacheType.EHCACHE, EhCacheCacheConfiguration.class.getName());mappings.put(CacheType.HAZELCAST, HazelcastCacheConfiguration.class.getName());mappings.put(CacheType.INFINISPAN, InfinispanCacheConfiguration.class.getName());mappings.put(CacheType.JCACHE, JCacheCacheConfiguration.class.getName());mappings.put(CacheType.COUCHBASE, CouchbaseCacheConfiguration.class.getName());mappings.put(CacheType.REDIS, RedisCacheConfiguration.class.getName());mappings.put(CacheType.CAFFEINE, CaffeineCacheConfiguration.class.getName());mappings.put(CacheType.SIMPLE, SimpleCacheConfiguration.class.getName());mappings.put(CacheType.NONE, NoOpCacheConfiguration.class.getName());MAPPINGS = Collections.unmodifiableMap(mappings);
}/*** 根据CacheType获取配置类*/
static String getConfigurationClass(CacheType cacheType) {String configurationClassName = MAPPINGS.get(cacheType);Assert.state(configurationClassName != null, () -> "Unknown cache type " + cacheType);return configurationClassName;
}/*** 根据配置类获取CacheType*/
static CacheType getType(String configurationClassName) {for (Map.Entry<CacheType, String> entry : MAPPINGS.entrySet()) {if (entry.getValue().equals(configurationClassName)) {return entry.getKey();}}throw new IllegalStateException("Unknown configuration class " + configurationClassName);
}

2.5 CacheType

缓存类型的枚举，按照优先级定义；

GENERIC     // Generic caching using 'Cache' beans from the context.
JCACHE      // JCache (JSR-107) backed caching.
EHCACHE     // EhCache backed caching.
HAZELCAST   // Hazelcast backed caching.
INFINISPAN  // Infinispan backed caching.
COUCHBASE   // Couchbase backed caching.
REDIS       // Redis backed caching.
CAFFEINE    // Caffeine backed caching.
SIMPLE      // Simple in-memory caching.
NONE        // No caching.

2.4 CacheCondition

它是所有缓存配置使用的通用配置条件；

2.4.1 准备工作

介绍之前先看一些CacheCondition类使用的地方，可以看到是各种缓存类型类型的配置类使用了它。
在这里插入图片描述

@Conditional注解的作用是什么？
——请看这篇文章@Conditional 注解有什么用？

说穿了，就是根据注解参数Condition实现类（这里是CacheCondition类）的matches方法返回，来判断是否加载这个配置类。

2.4.2 CacheCondition核心代码

/*** 匹配逻辑*/
@Override
public ConditionOutcome getMatchOutcome(ConditionContext context, AnnotatedTypeMetadata metadata) {String sourceClass = "";if (metadata instanceof ClassMetadata) {sourceClass = ((ClassMetadata) metadata).getClassName();}ConditionMessage.Builder message = ConditionMessage.forCondition("Cache", sourceClass);Environment environment = context.getEnvironment();try {// 获取配置文件中指定的CacheTypeBindResult<CacheType> specified = Binder.get(environment).bind("spring.cache.type", CacheType.class);if (!specified.isBound()) {// 不存在则根据CacheConfiguration.mappings自上而下匹配合适的CacheConfigurationreturn ConditionOutcome.match(message.because("automatic cache type"));}CacheType required = CacheConfigurations.getType(((AnnotationMetadata) metadata).getClassName());// 存在则比较CacheType是否一致if (specified.get() == required) {return ConditionOutcome.match(message.because(specified.get() + " cache type"));}}catch (BindException ex) {}return ConditionOutcome.noMatch(message.because("unknown cache type"));
}

三、常见的CacheConfiguration

3.1 RedisCacheConfiguration

它是Redis缓存配置；

// Bean方法不被代理
@Configuration(proxyBeanMethods = false)
// RedisConnectionFactory在类路径上存在
@ConditionalOnClass(RedisConnectionFactory.class)
// 在RedisAutoConfiguration之后自动配置
@AutoConfigureAfter(RedisAutoConfiguration.class)
// RedisConnectionFactory实例存在
@ConditionalOnBean(RedisConnectionFactory.class)
// CacheManager实例不存在
@ConditionalOnMissingBean(CacheManager.class)
// 根据CacheCondition选择导入
@Conditional(CacheCondition.class)
class RedisCacheConfiguration {/*** 创建RedisCacheManager*/@BeanRedisCacheManager cacheManager(CacheProperties cacheProperties, CacheManagerCustomizers cacheManagerCustomizers,ObjectProvider<org.springframework.data.redis.cache.RedisCacheConfiguration> redisCacheConfiguration,ObjectProvider<RedisCacheManagerBuilderCustomizer> redisCacheManagerBuilderCustomizers,RedisConnectionFactory redisConnectionFactory, ResourceLoader resourceLoader) {// 使用RedisCachemanagerRedisCacheManagerBuilder builder = RedisCacheManager.builder(redisConnectionFactory).cacheDefaults(determineConfiguration(cacheProperties, redisCacheConfiguration, resourceLoader.getClassLoader()));List<String> cacheNames = cacheProperties.getCacheNames();if (!cacheNames.isEmpty()) {// 设置CacheProperties配置的值builder.initialCacheNames(new LinkedHashSet<>(cacheNames));}if (cacheProperties.getRedis().isEnableStatistics()) {// 设置CacheProperties配置的值builder.enableStatistics();}// 装饰redisCacheManagerBuilderredisCacheManagerBuilderCustomizers.orderedStream().forEach((customizer) -> customizer.customize(builder));// 装饰redisCacheManagerreturn cacheManagerCustomizers.customize(builder.build());}/*** 如果redisCacheConfiguration不存在则使用默认值*/private org.springframework.data.redis.cache.RedisCacheConfiguration determineConfiguration(CacheProperties cacheProperties,ObjectProvider<org.springframework.data.redis.cache.RedisCacheConfiguration> redisCacheConfiguration,ClassLoader classLoader) {return redisCacheConfiguration.getIfAvailable(() -> createConfiguration(cacheProperties, classLoader));}/*** 根据CacheProperties创建默认RedisCacheConfigutation*/private org.springframework.data.redis.cache.RedisCacheConfiguration createConfiguration(CacheProperties cacheProperties, ClassLoader classLoader) {Redis redisProperties = cacheProperties.getRedis();org.springframework.data.redis.cache.RedisCacheConfiguration config =     org.springframework.data.redis.cache.RedisCacheConfiguration.defaultCacheConfig();config = config.serializeValuesWith(SerializationPair.fromSerializer(new JdkSerializationRedisSerializer(classLoader)));// 优先使用CacheProperties的值，若存在的话if (redisProperties.getTimeToLive() != null) {config = config.entryTtl(redisProperties.getTimeToLive());}if (redisProperties.getKeyPrefix() != null) {config = config.prefixCacheNameWith(redisProperties.getKeyPrefix());}if (!redisProperties.isCacheNullValues()) {config = config.disableCachingNullValues();}if (!redisProperties.isUseKeyPrefix()) {config = config.disableKeyPrefix();}return config;}
}

3.2 SimpleCacheConfiguration

// Bean方法不被代理
@Configuration(proxyBeanMethods = false)
// 不存在CacheManager实例
@ConditionalOnMissingBean(CacheManager.class)
// 根据CacheCondition选择导入
@Conditional(CacheCondition.class)
class SimpleCacheConfiguration {/*** 创建CacheManager*/@BeanConcurrentMapCacheManager cacheManager(CacheProperties cacheProperties,CacheManagerCustomizers cacheManagerCustomizers) {// 使用ConcurrentMapCacheManagerConcurrentMapCacheManager cacheManager = new ConcurrentMapCacheManager();List<String> cacheNames = cacheProperties.getCacheNames();// 如果CacheProperties配置了cacheNames，则使用if (!cacheNames.isEmpty()) {// 配置了cacheNames，则不支持动态创建缓存了cacheManager.setCacheNames(cacheNames);}// 装饰ConcurrentMapCacheManagerreturn cacheManagerCustomizers.customize(cacheManager);}
}