The difference between GET and POST for a simple web login program

JSP program

　　First, write a JSP program to submit the form:

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
    String path = request.getContextPath();
    String basePath = request.getScheme() + "://"
            + request.getServerName() + ":" + request.getServerPort()
            + path + "/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">

<title>My JSP 'login.jsp' starting page</title>

<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
    <link rel="stylesheet" type="text/css" href="styles.css">
    -->

</head>

<body>
    <form action="Login"  method="post">
        username: <input type="text" name="username"><br>
        password: <input type="password" name="password"><br>
        <input type="submit" value="submit">   
        <input type="reset" value="reset">
    </form>
</body>
</html>

Note that the action is the url-pattern in web.xml, (the relative path is given here), so that the corresponding servlet program can be started after submission.

Servlet program

　　Then, write a servlet program to display the received data:

package demo;


import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class LoginServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException
    {
        processLogin(req, resp);

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

    }
    
    private void processLogin(HttpServletRequest req, HttpServletResponse resp)
            throws IOException
    {
        String username = req.getParameter("username");
        String password = req.getParameter("password");

        resp.setContentType("text/html");

        PrintWriter out = resp.getWriter();

        out.println("<html><head><title>Login Result</title></head>");
        out.println("<body> username: " + username + "<br>");
        out.println("password: " + password + "</body></html>");

        out.flush();
    }
}

web.xml

　　Create a mapping relationship in web.xml:

	<servlet>
		<servlet-name>LoginResult</servlet-name>
		<servlet-class>demo.LoginServlet</servlet-class>
	</servlet>
	<servlet-mapping>
		<servlet-name>LoginResult</servlet-name>
		<url-pattern>/Login</url-pattern>
	</servlet-mapping>

Start the browser and enter: http://localhost:8050/WebApi2d/Login.jsp

　　After submitting, the address bar shows: http://localhost:8050/WebApi2d/Login

　　There is no username and password information behind. This is the POST method

Difference between get and post methods:

　　1. The results presented by the browser address bar are different (appearance);

　　2. When uploading files through a browser, you must use the post method instead of the get method.

　　3. Access server-side resources by entering the URL in the browser address bar, all of which are requested by the get method.