【1】CacheAutoConfiguration
在SpringBoot中，Cache的自动配置类，源码如下。
/**
* {@link EnableAutoConfiguration Auto-configuration} for the cache abstraction. Creates a
* {@link CacheManager} if necessary when caching is enabled via {@link EnableCaching}.
* <p>
* Cache store can be auto-detected or specified explicitly via configuration.
*
* @author Stephane Nicoll
* @since 1.3.0
* @see EnableCaching
*/
@Configuration
@ConditionalOnClass(CacheManager.class)
@ConditionalOnBean(CacheAspectSupport.class)
@ConditionalOnMissingBean(value = CacheManager.class, name = "cacheResolver")
@EnableConfigurationProperties(CacheProperties.class)
@AutoConfigureBefore(HibernateJpaAutoConfiguration.class)
@AutoConfigureAfter({ CouchbaseAutoConfiguration.class, HazelcastAutoConfiguration.class,
RedisAutoConfiguration.class })
@Import(CacheConfigurationImportSelector.class)
public class CacheAutoConfiguration {
static final String VALIDATOR_BEAN_NAME = "cacheAutoConfigurationValidator";
@Bean
@ConditionalOnMissingBean
public CacheManagerCustomizers cacheManagerCustomizers(
ObjectProvider<List<CacheManagerCustomizer<?>>> customizers) {
return new CacheManagerCustomizers(customizers.getIfAvailable());
}
@Bean
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public static CacheManagerValidatorPostProcessor cacheAutoConfigurationValidatorPostProcessor() {
return new CacheManagerValidatorPostProcessor();
}
@Bean(name = VALIDATOR_BEAN_NAME)
public CacheManagerValidator cacheAutoConfigurationValidator() {
return new CacheManagerValidator();
}
@Configuration
@ConditionalOnClass(LocalContainerEntityManagerFactoryBean.class)
@ConditionalOnBean(AbstractEntityManagerFactoryBean.class)
protected static class CacheManagerJpaDependencyConfiguration
extends EntityManagerFactoryDependsOnPostProcessor {
public CacheManagerJpaDependencyConfiguration() {
super("cacheManager");
}
}
/**
* {@link BeanFactoryPostProcessor} to ensure that the {@link CacheManagerValidator}
* is triggered before {@link CacheAspectSupport} but without causing early
* instantiation.
*/
static class CacheManagerValidatorPostProcessor implements BeanFactoryPostProcessor {
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory)
throws BeansException {
for (String name : beanFactory.getBeanNamesForType(CacheAspectSupport.class,
false, false)) {
BeanDefinition definition = beanFactory.getBeanDefinition(name);
definition.setDependsOn(
append(definition.getDependsOn(), VALIDATOR_BEAN_NAME));
}
}
private String[] append(String[] array, String value) {
String[] result = new String[array == null ? 1 : array.length + 1];
if (array != null) {
System.arraycopy(array, 0, result, 0, array.length);
}
result[result.length - 1] = value;
return result;
}
}
/**
* Bean used to validate that a CacheManager exists and provide a more meaningful
* exception.
*/
static class CacheManagerValidator {
@Autowired
private CacheProperties cacheProperties;
@Autowired(required = false)
private CacheManager cacheManager;
@PostConstruct
public void checkHasCacheManager() {
Assert.notNull(this.cacheManager,
"No cache manager could "
+ "be auto-configured, check your configuration (caching "
+ "type is '" + this.cacheProperties.getType() + "')");
}
}
/**
* {@link ImportSelector} to add {@link CacheType} configuration classes.
*/
static class CacheConfigurationImportSelector implements ImportSelector {
//拿到系统中的所有缓存配置类
@Override
public 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;
}
}
}如下所示，添加了11个缓存配置类：
0 = "org.springframework.boot.autoconfigure.cache.GenericCacheConfiguration"
1 = "org.springframework.boot.autoconfigure.cache.JCacheCacheConfiguration"
2 = "org.springframework.boot.autoconfigure.cache.EhCacheCacheConfiguration"
3 = "org.springframework.boot.autoconfigure.cache.HazelcastCacheConfiguration"
4 = "org.springframework.boot.autoconfigure.cache.InfinispanCacheConfiguration"
5 = "org.springframework.boot.autoconfigure.cache.CouchbaseCacheConfiguration"
6 = "org.springframework.boot.autoconfigure.cache.RedisCacheConfiguration"
7 = "org.springframework.boot.autoconfigure.cache.CaffeineCacheConfiguration"
8 = "org.springframework.boot.autoconfigure.cache.GuavaCacheConfiguration"
9 = "org.springframework.boot.autoconfigure.cache.SimpleCacheConfiguration"
10 = "org.springframework.boot.autoconfigure.cache.NoOpCacheConfiguration"
【2】默认缓存配置
在application.properties中开启debug:debug=true。在控制台即可打印自动配置报告：
默认使用的是SimpleCacheConfiguration！
其源码如下：
/**
* Simplest cache configuration, usually used as a fallback.
*
* @author Stephane Nicoll
* @since 1.3.0
*/
@Configuration
@ConditionalOnMissingBean(CacheManager.class)
@Conditional(CacheCondition.class)
class SimpleCacheConfiguration {
private final CacheProperties cacheProperties;
private final CacheManagerCustomizers customizerInvoker;
SimpleCacheConfiguration(CacheProperties cacheProperties,
CacheManagerCustomizers customizerInvoker) {
this.cacheProperties = cacheProperties;
this.customizerInvoker = customizerInvoker;
}
// 注册了ConcurrentMapCacheManager
@Bean
public ConcurrentMapCacheManager cacheManager() {
ConcurrentMapCacheManager cacheManager = new ConcurrentMapCacheManager();
List<String> cacheNames = this.cacheProperties.getCacheNames();
if (!cacheNames.isEmpty()) {
cacheManager.setCacheNames(cacheNames);
}
return this.customizerInvoker.customize(cacheManager);
}
}ConcurrentMapCacheManager (可以获取和创建ConcurrentMapCache)源码如下：
/**
* {@link CacheManager} implementation that lazily builds {@link ConcurrentMapCache}
* instances for each {@link #getCache} request. Also supports a 'static' mode where
* the set of cache names is pre-defined through {@link #setCacheNames}, with no
* dynamic creation of further cache regions at runtime.
*
* <p>Note: This is by no means a sophisticated CacheManager; it comes with no
* cache configuration options. However, it may be useful for testing or simple
* caching scenarios. For advanced local caching needs, consider
* {@link org.springframework.cache.jcache.JCacheCacheManager},
* {@link org.springframework.cache.ehcache.EhCacheCacheManager},
* {@link org.springframework.cache.caffeine.CaffeineCacheManager} or
* {@link org.springframework.cache.guava.GuavaCacheManager}.
*
* @author Juergen Hoeller
* @since 3.1
* @see ConcurrentMapCache
*/
public class ConcurrentMapCacheManager implements CacheManager, BeanClassLoaderAware {
private final ConcurrentMap<String, Cache> cacheMap = new ConcurrentHashMap<String, Cache>(16);
private boolean dynamic = true;
private boolean allowNullValues = true;
private boolean storeByValue = false;
private SerializationDelegate serialization;
/**
* Construct a dynamic ConcurrentMapCacheManager,
* lazily creating cache instances as they are being requested.
*/
public ConcurrentMapCacheManager() {
}
/**
* Construct a static ConcurrentMapCacheManager,
* managing caches for the specified cache names only.
*/
public ConcurrentMapCacheManager(String... cacheNames) {
setCacheNames(Arrays.asList(cacheNames));
}
/**
* Specify the set of cache names for this CacheManager's 'static' mode.
* <p>The number of caches and their names will be fixed after a call to this method,
* with no creation of further cache regions at runtime.
* <p>Calling this with a {@code null} collection argument resets the
* mode to 'dynamic', allowing for further creation of caches again.
*/
public void setCacheNames(Collection<String> cacheNames) {
if (cacheNames != null) {
for (String name : cacheNames) {
this.cacheMap.put(name, createConcurrentMapCache(name));
}
this.dynamic = false;
}
else {
this.dynamic = true;
}
}
/**
* Specify whether to accept and convert {@code null} values for all caches
* in this cache manager.
* <p>Default is "true", despite ConcurrentHashMap itself not supporting {@code null}
* values. An internal holder object will be used to store user-level {@code null}s.
* <p>Note: A change of the null-value setting will reset all existing caches,
* if any, to reconfigure them with the new null-value requirement.
*/
public void setAllowNullValues(boolean allowNullValues) {
if (allowNullValues != this.allowNullValues) {
this.allowNullValues = allowNullValues;
// Need to recreate all Cache instances with the new null-value configuration...
recreateCaches();
}
}
/**
* Return whether this cache manager accepts and converts {@code null} values
* for all of its caches.
*/
public boolean isAllowNullValues() {
return this.allowNullValues;
}
/**
* Specify whether this cache manager stores a copy of each entry ({@code true}
* or the reference ({@code false} for all of its caches.
* <p>Default is "false" so that the value itself is stored and no serializable
* contract is required on cached values.
* <p>Note: A change of the store-by-value setting will reset all existing caches,
* if any, to reconfigure them with the new store-by-value requirement.
* @since 4.3
*/
public void setStoreByValue(boolean storeByValue) {
if (storeByValue != this.storeByValue) {
this.storeByValue = storeByValue;
// Need to recreate all Cache instances with the new store-by-value configuration...
recreateCaches();
}
}
/**
* Return whether this cache manager stores a copy of each entry or
* a reference for all its caches. If store by value is enabled, any
* cache entry must be serializable.
* @since 4.3
*/
public boolean isStoreByValue() {
return this.storeByValue;
}
@Override
public void setBeanClassLoader(ClassLoader classLoader) {
this.serialization = new SerializationDelegate(classLoader);
// Need to recreate all Cache instances with new ClassLoader in store-by-value mode...
if (isStoreByValue()) {
recreateCaches();
}
}
@Override
public Collection<String> getCacheNames() {
return Collections.unmodifiableSet(this.cacheMap.keySet());
}
//根据名字获取Cache组件
@Override
public Cache getCache(String name) {
Cache cache = this.cacheMap.get(name);
if (cache == null && this.dynamic) {
synchronized (this.cacheMap) {
cache = this.cacheMap.get(name);
if (cache == null) {
cache = createConcurrentMapCache(name);
this.cacheMap.put(name, cache);
}
}
}
return cache;
}
private void recreateCaches() {
for (Map.Entry<String, Cache> entry : this.cacheMap.entrySet()) {
entry.setValue(createConcurrentMapCache(entry.getKey()));
}
}
/**
* Create a new ConcurrentMapCache instance for the specified cache name.
* @param name the name of the cache
* @return the ConcurrentMapCache (or a decorator thereof)
*/
protected Cache createConcurrentMapCache(String name) {
SerializationDelegate actualSerialization = (isStoreByValue() ? this.serialization : null);
return new ConcurrentMapCache(name, new ConcurrentHashMap<Object, Object>(256),
isAllowNullValues(), actualSerialization);
}
}ConcurrentMapCache作用：将数据保存在ConcurrentMap中，并进行获取。
【3】运行流程
这里以注解@Cacheable为例，过程如下。
① 方法运行之前，先去Cache组件中进行查询。Cache组件是CacheManager根据cacheNames获取，如果没有则自动创建。
② 根据key 从Cache中查询缓存的内容，默认key为使用keyGenerator(默认为SimpleKeyGenerator)生成的。
SimpleKeyGenerator的生成key的策略：
- 如果没有参数，则key = new SimpleKey();
- 如果有一个参数，key = 参数值；
- 如果有多个参数，key = new SimpleKey(params)。
③ 如果没有查到缓存就调用目标方法
④ 将目标方法的返回结果放入缓存中
⑤ 如果从缓存中查到了就不调用目标方法，直接从缓存中获取然后返回
CacheAspectSupport中源码示例如下：
private Cache.ValueWrapper findCachedItem(Collection<CacheOperationContext> contexts) {
Object result = CacheOperationExpressionEvaluator.NO_RESULT;
for (CacheOperationContext context : contexts) {
if (isConditionPassing(context, result)) {
Object key = generateKey(context, result);
Cache.ValueWrapper cached = findInCaches(context, key);
if (cached != null) {
return cached;
}
else {
if (logger.isTraceEnabled()) {
logger.trace("No cache entry for key '" + key + "' in cache(s) " + context.getCacheNames());
}
}
}
}
return null;
}