java threadlocal singleton - 它是什么？
通俗地说，当有人说一个对象是 Java 中的线程本地单例时，这意味着什么？我参加了一个关于 Java Server Faces 的讲座，每次谈到 FacesContext 时，讲师总是提醒我们它是一个线程本地单例。
In layman speak, what does it mean when somebody says an object is a threadlocal singleton in Java? I was at a lecture about Java Server Faces, and everytime the FacesContext was spoken of - the instructor always reminded us that it is a threadlocal singleton.
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FacesContext每个线程。FacesServlet创建一个ThreadLocal位于 HTTP 的开头servlet 请求并在与 HTTP servlet 请求关联的 HTTP servlet 响应末尾将其删除。每当您执行FacesContext#getCurrentInstance()在 JSF 代码中，在整个 HTTP servlet 请求/响应处理过程中，您将始终获得同一个实例。由于 HTTP servlet 请求由不同的线程执行，并且 FacesContext 实例作为线程局部变量附加到单个线程，因此没有两个 HTTP servlet 请求共享相同的 FacesContext实例。
There is only one unique instance of the
FacesContextper thread.The
FacesServletcreates aThreadLocal<FacesContext>on the beginning of the HTTP servlet request and removes it on the end of the HTTP servlet response associated with the HTTP servlet request. Whenever you do aFacesContext#getCurrentInstance()in your JSF code, you'll always get the one and the same instance throughout the entire HTTP servlet request/response processing.Since HTTP servlet requests are executed by distinct threads and the
FacesContextinstance is attached as thread local variable to a single thread, no two HTTP servlet requests share the sameFacesContextinstance.