Spring When initializing DispatcherServlet multiple times, its internal states like handlerAdapters etc. will be cleared first and then set

Affects: \

Background: Tomcat 8.5, using Spring Boot 2.6.8 and Spring 5.3.20 to setup one DispatcherServlet instance to multiple servlet mapping paths. For example: map it to both "/a_path/*" and "/b_path/*", the "loadOnStartUp" are not set.

Steps to reproduce the problem: Step 1 start the service

Step 2 request to "/a_path/api1" It's the first time to access "/a_path/*", Tomcat will initialize the DispatcherServlet instance by invoking its method DispatcherServlet#initStrategies. Then its internal states like handlerMappings, handlerAdapters will be set.

Step 3 request to "/b_path/api2" It's the first time to access "/b_path/*", Tomcat will initialize the same DispatcherServlet instance by invoking its method DispatcherServlet#initStrategies again.
The problem is here, the initialization methods like DispatcherServlet#initHandlerAdapters will clear previous state first before set them again:

  private void initHandlerAdapters(ApplicationContext context) {
        //Step 3a:clear handlerAdapters first 
    this.handlerAdapters = null; 
         ...
        //Step 3b: set handlerAdapters again
         ...
   }

Assume now Step 3 processing is between step 3a and step 3b, the handlerAdapters is cleared as null at this moment, it happens a new request "/a_path/api3" just comes, it will be processed in DispatcherServlet#doDispatch and found no handlerAdapters here, so it will end up with an error: "No adapter for handler [xxx]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler"

Comment From: snicoll

I don't understand how the same DispatcherServlet instance could be reused. I don't think reusing the same instance, and having the servlet initalization callback invoked several times is supported. Can you please share a small sample that showcase what you've described? You can attach a zip to this issue or push the code to a separate GitHub repository.

Comment From: spring-projects-issues

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