Servlet and JSP are the main technologies to develop the web applications.

Servlet was considered superior to CGI. Servlet technology doesn't create process, rather it creates thread to handle request. The advantage of creating thread over process is that it doesn't allocate separate memory area. Thus many subsequent requests can be easily handled by servlet.

Problem in Servlet technology Servlet needs to recompile if any designing code is modified. It doesn't provide separation of concern. Presentation and Business logic are mixed up.

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JSP overcomes almost all the problems of Servlet. It provides better separation of concern, now presentation and business logic can be easily separated. You don't need to redeploy the application if JSP page is modified. JSP provides support to develop web application using JavaBean, custom tags and JSTL so that we can put the business logic separate from our JSP that will be easier to test and debug.

model 1 architecture

As you can see in the above figure, there is picture which show the flow of the model1 architecture.

Browser sends request for the JSP page

JSP accesses Java Bean and invokes business logic

Java Bean connects to the database and get/save data

Response is sent to the browser which is generated by JS 

https://www.javatpoint.com/model-1-and-model-2-mvc-architecture