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This article introduces the relevant knowledge of "what is the complete process of Java servlet implementation". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

Summary:

It mainly describes the whole execution process from browser to server, and then from server to browser.

Browser request

When the browser requests from the server, the server will not execute our class directly, but will look for the pathname in web.xml

①: the first step is that the browser enters the access path and carries the request line, header, and body

②: the second step is to find the registered servlet name according to the access path, namely the demo in the figure

③: step 3, find the corresponding servlet name according to the mapping

③: step 4, find our fully qualified class name based on the servlet name, that is, the class we wrote ourselves

Server creates objects

①: after the server finds the fully qualified class name, it creates an object through reflection, as well as a servletConfig, which stores some initialization information (note that the server will only create a servlet object once, so there is only one servletConfig)

Call the init method

①: after the object is created, we first need to execute the init method, but we find that there is no init method under our custom class, so the program will look in its parent class HttpServlet

②: we found that there was no init method in HttpServlet, so we continued to look up, both in its parent class GenericServlet, and when we found the init method in GenericServlet, we executed the init method (overridden the init method in interface Servlet)

Note:

When the public void init (ServletConfig config) method is executed in GenericServlet, the init () method with no method body is called to facilitate the developer. If the developer needs to implement some functions in the initialization process, he can override this method.

Call the service method

Next, the server first creates two objects: the ServletRequest request object and the ServletResponse response object, which are used to encapsulate the browser's request data and the response data to the browser.

①: then the server will by default look for the service (ServletRequest req, ServletResponse res) method in the class we wrote, but it doesn't exist in DemoServlet, so it will look for it in its parent class.

②: if you find this method in the parent class HttpServlet, call this method directly and pass in the two previously created objects

③: then override the two parameters passed in and call another service method under HttpServlet

④: then execute the service (HttpServletRequest req, HttpServletResponse resp) method, which determines the request mode and executes doGet and doPost, but the doGet and doPost methods have been rewritten by ourselves, so the method we rewritten will be executed

Seeing here, you may be wondering: why don't we just rewrite the service method?

Because if we rewrite the service method, we need to rewrite the override and a series of security judgments, and there will be security risks.

Respond to the browser

Finally, after processing the data, respond to the data to the browser

This is the end of the content of "what is the complete process implemented by Java servlet". Thank you for reading. If you want to know more about the industry, you can follow the website, the editor will output more high-quality practical articles for you!

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