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In depth source code analysis servlet first program

2022-04-23 05:56:00 【ShuangTwo】

First of all give Servlet Program , Then let it be realized . Write a simple Servlet Program , Just write two files . One is Servlet Of Java Program , One is configuration web.xml.

Servlet It is inherited from HttpServlet, Need to rewrite doGet() and doPost() Two sides .

HelloServlet

package com.java.servlet;

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

public class HelloServlet extends HttpServlet {
    

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
        resp.setContentType("text/html;charset=utf-8");   // Set the response type to HTML file 
        PrintWriter out = resp.getWriter();  // Get the response output stream 
        out.println("<html>");
        out.println("<title>God of Night! </title>");
        out.println("<body>");
        out.println("<h1>Without a bit of cold, how can the plum blossoms smell so sweet.</h1>");
        out.println("</body>");
        out.println("</html>");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
        super.doPost(req, resp);
    }
}

Analysis of the code ：
First response call setContentType() Method , Set the type of response content .
This setContentType The way is by response Called ,response yes HttpServletResponse Instance object of , Click in HttpServletResponse Can see ,HttpServletResponse Inherited ServletResponse
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ServletResponse Interface defined setContentType Method , And later to say getWriter Method .
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see setContentType Implementation class of , Find out ServletResponseWrapper Realized ServletResponse All the methods in the interface .
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The whole flow chart is as follows ：
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summary ：
ServletResponse Defines all methods of response ,ServletResponseWrapper and HttpServletResponseWrapper Jointly implement these methods , then HttpServletResponse Inherit ServletResponse, all HttpServletResponse You can use it directly ServletResponse All the ways .

About HttpServletRequest Flow chart and source code analysis HttpServletResponse cut from the same cloth .

Another one resp.getWriter(), This method is used to get the response output stream , Send the information data to the front page , If you pass System.out.println(); Information can only be output to the background .

web.xml

<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
         http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0"
         metadata-complete="true">
    
    <servlet>
        <servlet-name>HelloServlet</servlet-name>
        <servlet-class>com.java.servlet.HelloServlet</servlet-class>
    </servlet>
    
    <servlet-mapping>
        <servlet-name>HelloServlet</servlet-name>
        <url-pattern>/geeks</url-pattern>
    </servlet-mapping>

</web-app>

web.xml register servlet, take servlet After the class and package are registered , adopt url-pattern Set up URL Jump to what we wrote servlet Program .

summary ：

  1. To write Servlet Program , Define the content of the page
  2. register Servlet Program , Definition URL Access address

版权声明
本文为[ShuangTwo]所创，转载请带上原文链接，感谢
https://yzsam.com/2022/04/202204230541368040.html

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