2021.8.7 note Servlet

summary

I've been doing it for a long time 404... The solution is deployment Inside application context Change to /

servlet Execution principle

Life cycle approach

Annotation configuration

import javax.servlet.*;
import javax.servlet.annotation.WebServlet;
import java.io.IOException;

@WebServlet("/demo3")
public class ServletPratice implements Servlet {
    
    @Override
    public void init(ServletConfig servletConfig) throws ServletException {
    

    }

    @Override
    public ServletConfig getServletConfig() {
    
        return null;
    }

    @Override
    public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {
    
        System.out.println("servlet4.0...");
    }

    @Override
    public String getServletInfo() {
    
        return null;
    }

    @Override
    public void destroy() {
    

    }
}

there value No , because value Refers to the most important , Obviously, the most important thing here is urlpattern, only one value You can put "value" delete .

idea And tomcat Related configuration

HttpServlet

It mainly involves forms get and post
Can be rewritten doget and dopost Method

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet("/demo4")
public class DemoClass extends HttpServlet {
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
        System.out.println("doget...");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
        System.out.println("dopost...");
    }
}

Always forgetting to add virtual directories leads to 404..

Set a mark ： genericServlet

urlpattern To configure

//@WebServlet({"/de1","/de2","/de3"})
//@WebServlet({"/user/gogo)  Two level directory  
//@WebServlet({"/*"})  Display everything you enter , But the priority is the lowest 
//@WebServlet({"*.do"})  No matter which one you want to add .do, Cannot add /