Brief request process

Let's talk about the process of a request responding from the browser to the server

1. First, there is a domain name corresponding to the local query ip, Can't find anything like DNS The server requests to find the corresponding IP, Can't find the upper layer … The root domain name server cannot be found and an error is reported , Any section found will return ip
2. If you use tcp The protocol needs three handshakes to communicate with the server （ Customer requests confirmation , Server confirmation , Customer service confirms receipt of confirmation ）, Received reply retransmission, etc , If you use UDP The protocol does not require a connection and a reply to send directly .
3. send out http request , The server obtains the parsing encapsulation request information and distributes it to the corresponding processing return results .
4. Four waves （ Customer requests disconnection , Server received , Server notification shutdown , Customer confirms receipt of closing confirmation ） Wait for the operation
**ps:** The essence of computer communication is the communication between processes , A computer is a ip Address , The corresponding port number is the process corresponding to the agreed port in the computer , It is the network interface between the transport layer and the application layer . such as tomcat Engagement listening 8080 port , A message through ip After arriving at the server, the port number is resolved as 8080 And then handle it. Otherwise, it will not be accepted .

tomcat Process request

connector Accept the request, encapsulate it and pass it to container To deal with ,container Call the corresponding servlet Processing requests ,dispatcherServlet It's just one. servlet, Handle all requests ,dispatcherServlet After receiving the request, process the mapper HandleMapper Look for the corresponding Handle, The corresponding... Is then executed through the processor adapter area Handle That's the controller , Then the execution result returns modelAndView, then dsipatchServlet Will pass through modelAndView To parse the rendered view and return it to the user .
Here's the picture , Just keep the picture in mind .

Tell me about your understanding of containers

Containers like tomcat The container is just a web The container is servlet Containers , The container is easy to be compared to the bucket , It's just something that looks easy to understand , such as Spring The container says that it is a container for all classes , On a deeper level , It doesn't have to be filled like a barrel , The reason why barreled water is easy to understand is that we can intuitively see that the water is packed in a visual range , go back to Spring Wait for these containers , Pretend to be a class , such as tomcat It's just servlet In fact, it is not filled like a barrel , It means management , such as tomcat Will be called upon request servlet The method of managing the life cycle of processing requests . image Spring The life cycle of container management classes is based on bean Find the corresponding class and call the corresponding function, such as initialization , Containers are like middlemen … Responsible for the management and allocation of relevant resources …