Servlet of three web components

The blogger's name is taken from 《 Shaun the Sheep 》 Shawn the lamb in the , The name is ： Sean , Transliterated as Sean, Take your own last name ： Archie , In order to conform to our reading habits , Connected to form ArchieSean. The blogger is currently a junior reading , Aiming to build blog into a technical stack of personal online notes , Be convenient for yourself and others . If there are any mistakes in the blog , Please point out , Thank you. .

servlet summary

Simply speaking , It is a server-side applet .
servlet It's an interface , It defines the java Class is accessed by the browser .

servlet Structure system

servlet Method

Pictured Realization servlet Interface , Rewrite its method .

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

public class Csdn implements Servlet {
    
    @Override
    // Initialization method , stay servlet Execute when created , And only once 
    public void init(ServletConfig servletConfig) throws ServletException {
    
    
        
    }

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

    @Override
    // How to provide services , Execute on each visit 
    public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {
    

    }

    @Override
    // return servlet Information about , For example, the author , Version, etc 
    public String getServletInfo() {
    
        return null;
    }

    @Override
    // Destruction method , Called when the server shuts down 
    public void destroy() {
    

    }
}

servlet Life cycle

1. born ： init Method execution , And only once ,servlet Be created .
   By default , On first visit ,servlet Be created , It can also be created when the server starts .
2. Alive ： perform service Method , Multiple executions .
3. Death ： destroy Method execution
   When the server is down , perform destriy Method ,servlet Be destroyed .

servlet Of xml To configure

be located WEB-INF Under the web.xml

<web-app>      
    <servlet>
        <servlet-name>HelloWorld</servlet-name>
        <servlet-class>com.xxx.servlet.HelloWorld</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>HelloWorld</servlet-name>
        <url-pattern>/HelloWorld</url-pattern>
    </servlet-mapping>
</web-app>  

servlet principle

As shown in the figure above ：

• When the server receives a server request , Can parse url route , Get access to servlet The resource path of .
• The server will look for web.xml file , Find the one consistent with the access path url-pattern Label content
• Then find the corresponding servlet-class label , Get servlet Full class name of
• Put this kind of class File loaded into memory （ Using reflection ：Class.forName（） To load the ）
• Create its object （ Reflection ：Class.newInstance（） Create objects ）
• call service Method

Servlet The annotation configuration of

@webServlet（value=" Access path "）

Add this annotation to servlet Class , There is no need for xml The configuration of the .

request and response I'll summarize in the next article . If there are any questions in the blog , Please leave a comment in the comment area , thank you .