我们可以看到:这个 Bug 是位于大名鼎鼎的 concurrent 包里面的 computeIfAbsent 方法。 这个Bug 在 JDK 9 里面被修复了,修复人是 Doug Lea。 而我们知道 ConcurrentHashMap 就是 Doug Lea 的大作,可以说是“谁污染谁治理”。 要了解这个 Bug 是怎么回事,就必须先了解下面这个方法是干啥的: java.util.concurrent...
A Hashtable is synchronized, while a HashMap is not. Thus, HashMap is preferred in single-threaded environments, while a Hashtable is suitable for multi-threaded environments. A HashMap provides its set of keys and a Java application can iterate over them. Thus, a HashMap is fail-fast. ...
* 缓存单例对象:beanName->beanInstance*/privatefinalMap<String, Object> singletonObjects =newConcurrentHashMap<>(256); 在一个CurrentHashMap中存储beanName到beanInstance的映射关系,其实这就是传说中的一级缓存,从代码可以看出,Spring在创建一个单例bean的时候,会先通过beanName从一级缓存中获取,当获取不到是...
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