如何从Java中的另一个线程访问ThreadLocal中的信息

Question

I am working with a Java web application backend. We have a Servlet that in the init() method has

public static final ThreadLocal<HttpServletRequest> REQUEST_HOLDER = new ThreadLocal<HttpServletRequest>();

In the service() method

public void service(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException

the Servlet then sets the value of REQUEST_HOLDER with the request.

REQUEST_HOLDER.set(request);

Later in the servlet, I want to do some heavy processing on another thread, but still reference the request from the ThreadLocal REQUEST_HOLDER, which is technically on a different thread. Is this possible? how? (new to multithreading)

Although this general concept has largely been addressed in ThreadLocal value access across different threads , I want to know if there is anything unique regarding servlets / http requests that might provide a different solution. If not, not.

Also is it possible to take the REQUEST_HOLDER ThreadLocal and override the get() method so that if it is null (as in when called from a different thread) it returns a different value? - thinking of storing the request somewhere else and have the get() return that value.

Answer 1

另一种解决方案而不是弄乱ThreadLocal机制，是从主线程中的请求对象中提取所有必要的数据，将其放入单独的数据对象中，然后将此对象提供给新线程。

Answer 2

A coworker suggested to me that when I start the new Thread, I should pass in the request. Then in the new thread I can set the ThreadLocal REQUEST_HOLDER with the request from the new thread. Thanks all for your answers

Answer 3

As per the Java documentation , ThreadLocal variables are initialized so that they are only visible to individual threads.

Of course any value can be shared, so one could just make the Object value returned by the ThreadLocal get() method accessible to other threads, but that defeats the purpose of having such a variable in the first place.