"Welcome To Ashok IT"				
			                  "Spring Boot and MicroServices"
                                            Topic : Spring MVC - Form Submission
                                            Date  : 22/11/2024
                                              (Session - 72)                               
_____________________________________________________________________________________________________________________________
Problem : Double Posting
==========================
* If a user refreshes a page after submitting a form, he may accidentally post the content again by using refresh button(F5)    resulting in duplicate submission, this causing duplicate record creation in database and it is known as "Double Posting      Problem (or) Double submitting form".

Example
=======
 1) When we deploy the webapplication into tomcat server will get loaded into browser window with below URL
    http://localhost:1234/29_SpringMVC_FormSubmission_App/ >>>>>>>>>>>>>>>> GET Request

 2) User can fill the data in the form and submit form to post Request Processor method, so that post request processor           method will read the data from Dispatcherservlet using annotation called @ModelAttribute.

 3) Post Request Processor Method will save form information into database table and If record got inserted successfully will     direct to another view page i.e.,confirmation.jsp with below browser URL.
    http://localhost:1234/29_SpringMVC_FormSubmission_App/sendEnquiryDetails >>>>>>>>>>>>>>>> After Submitting the form

 4) After rendering the confirmation.jsp page content into browser and user may try to refresh the page by using F5 key in        keyboard it will leads for inserting duplication record in database table.

==============================================
Example Application On Double Posting Problem
==============================================

web.xml
=======
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns = "https://jakarta.ee/xml/ns/jakartaee" xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation = "https://jakarta.ee/xml/ns/jakartaee https://jakarta.ee/xml/ns/jakartaee/web-app_5_0.xsd" version = "5.0">
  <display-name>AshokITFormSubmission</display-name>
      <servlet>
        <servlet-name>ashokit</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <load-on-startup>1</load-on-startup>
    </servlet>
    <servlet-mapping>
        <servlet-name>ashokit</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>
</web-app>

mvc-servlet.xml
===============
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:p="http://www.springframework.org/schema/p"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans
        https://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context
        https://www.springframework.org/schema/context/spring-context.xsd">

    
     <!--Enabling component scan feature-->
     <context:component-scan base-package="com.ashokit"/>
     
      <!--configuring the ViewResolver-->
      <bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/views/"></property>
        <property name="suffix" value=".jsp"></property>
      </bean>
      
       <bean id="jdbcTemplate" class="org.springframework.jdbc.core.JdbcTemplate">
		<constructor-arg name="dataSource" ref="datasource" />
	</bean>
	
	<context:property-placeholder location=""/>

	<bean id="datasource" class="org.springframework.jdbc.datasource.DriverManagerDataSource"
						   p:driverClassName="com.mysql.cj.jdbc.Driver"
						   p:url="jdbc:mysql://localhost:3306/springboot" 
						   p:username="root"
						   p:password="root" />
      
</beans>

EnquiryController.java
======================
package com.ashokit.controller;

import java.util.Map;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.servlet.ModelAndView;

import com.ashokit.beans.Enquiry;
import com.ashokit.services.EnquiryService;

@Controller
public class EnquiryController {
	
	@Autowired
	private EnquiryService enquiryService;	
	
	@RequestMapping("/")
	public ModelAndView getEnquiryPage() {
		ModelAndView mav = new ModelAndView("enquiryDetails");
		mav.addObject("enquiryForm", new Enquiry());
		return mav;
	}
	
	@RequestMapping(value="sendEnquiry",method = RequestMethod.POST)
	public ModelAndView processEnquiryDetails(@RequestParam Map<String,String> formData) {
		ModelAndView mav = new ModelAndView("confirmation");
		System.out.println("FormData::::" + formData);
		
		//creating the object For Enquiry class for storing form data
		Enquiry enquiry = new Enquiry();
		enquiry.setName(formData.get("firstName"));
		enquiry.setEmailId(formData.get("emailId"));
		enquiry.setContactNo(formData.get("contactNo"));
		enquiry.setCourseName(formData.get("courseName"));
		
		//sharing the data to view page
		mav.addObject("enquiryDetails", enquiry);
		
		return mav;
	}
	
	@RequestMapping(value="sendEnquiryDetails", method=RequestMethod.POST)
	public ModelAndView processEnquiry(@ModelAttribute("enquiryForm") Enquiry enquiry) {
		ModelAndView mav = new ModelAndView();
		//sharing the data to view page
		mav.addObject("enquiryDetails", enquiry);
	
		//service call
		boolean saveEnquiryFlag = enquiryService.saveEnquiryDetails(enquiry);
		
		if(saveEnquiryFlag) {
			mav.setViewName("confirmation");
			//mav.setViewName("enquiresInfo");
			//mav.addObject("enquiryInfo", enquiryService.getAllEnquires());
		}else {
			mav.setViewName("enquiryDetails");
		}
		
		return mav;
	}
}

confirmation.jsp
================
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="ISO-8859-1">
<title>confirmation.jsp</title>
</head>
<body>
   <div style='text-align:center'>
   		<div>Student Name  : <span>${enquiryDetails.name}</span></div>
   		<div>Course Name  : <span>${enquiryDetails.courseName}</span></div>
   		<div>Your Enquiry is Received for above Details Admin Team will connect with you shortly.....</div>
   </div>
</body>
</html>

DBTable Records
===============
2000	Mahesh	mahesh@gmail.com	123232		Angular		20-AUG-23
2001	Suresh	Suresh@gmail.com	1232323		React		20-AUG-23
2002	Suresh	Suresh@gmail.com	1232323		React		20-AUG-23
2003	Suresh	Suresh@gmail.com	123232323	Devops		21-AUG-23
2004	Ramesh	ramesh@gmail.com	1232323		SpringBoot	21-AUG-23
2005	Nagesh	Nagesh@gmail.com	1232323		Devops		21-AUG-23
2006	Nagesh	Nagesh@gmail.com	1232323		Devops		21-AUG-23
2007	Nagesh	Nagesh@gmail.com	1232323		Devops		21-AUG-23
2008	Nagesh	Nagesh@gmail.com	1232323		Devops		21-AUG-23

Solution : PRG Pattern
======================
* Post/Redirect/Get(PRG) is a web development design pattern that prevents the duplicate form submissions.

* Programatically we can implement this design pattern with following approach

   1) Post Request method having capability to redirect the request to GET Request after submitting the form.

   2) In the Spring MVC we can have the option to redirect the request from one request processor method to another request         method using "redirect" attribute.

   3) Please find the below code snippet for how we can redirect the request between request processor methods

         @RequestMapping(value="processEnquiryForm", method=RequestMethod.POST)
         public String processEnquiry(){

             return "redirect:enquiryList";

         }

         @RequestMapping(value="enquiryList,method=RequestMethod.GET)
         public String displayEnquiryList(){
         
               return "enquiryList";
         }

=========================================
Example Application On PRG Design Pattern
=========================================

web.xml
=======
<!DOCTYPE web-app PUBLIC
 "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
 "http://java.sun.com/dtd/web-app_2_3.dtd" >

<web-app>
  <display-name>Archetype Created Web Application</display-name>
  <servlet>
     <servlet-name>mvc</servlet-name>
     <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
     <load-on-startup>25</load-on-startup>
  </servlet>
  
   <servlet-mapping>
      <servlet-name>mvc</servlet-name>
      <url-pattern>/</url-pattern>
   </servlet-mapping>
</web-app>

mvc-servlet.xml
===============
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:p="http://www.springframework.org/schema/p"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans
        https://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context
        https://www.springframework.org/schema/context/spring-context.xsd">

    
     <!--Enabling component scan feature-->
     <context:component-scan base-package="com.ashokit"/>
     
      <!--configuring the ViewResolver-->
      <bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/views/"></property>
        <property name="suffix" value=".jsp"></property>
      </bean>
      
    <bean id="jdbcTemplate" class="org.springframework.jdbc.core.JdbcTemplate">
		<constructor-arg name="dataSource" ref="datasource" />
	</bean>
	
	<context:property-placeholder location=""/>

	<bean id="datasource" class="org.springframework.jdbc.datasource.DriverManagerDataSource"
						   p:driverClassName="com.mysql.cj.jdbc.Driver"
						   p:url="jdbc:mysql://localhost:3306/springboot" 
						   p:username="root"
						   p:password="root" />
      
</beans>

package com.ashokit.controller;

import java.util.Map;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.mvc.support.RedirectAttributes;

import com.ashokit.beans.Enquiry;
import com.ashokit.services.EnquiryService;

import jakarta.servlet.http.HttpServletRequest;

@Controller
public class EnquiryController {
	
	@Autowired
	private EnquiryService enquiryService;	
	
	@RequestMapping("/")
	public ModelAndView getEnquiryPage() {
		ModelAndView mav = new ModelAndView("enquiryDetails");
		mav.addObject("enquiryForm", new Enquiry());
		return mav;
	}
	
	@RequestMapping(value="sendEnquiry",method = RequestMethod.POST)
	public ModelAndView processEnquiryDetails(@RequestParam Map<String,String> formData) {
		ModelAndView mav = new ModelAndView("confirmation");
		System.out.println("FormData::::" + formData);
		
		//creating the object For Enquiry class for storing form data
		Enquiry enquiry = new Enquiry();
		enquiry.setName(formData.get("firstName"));
		enquiry.setEmailId(formData.get("emailId"));
		enquiry.setContactNo(formData.get("contactNo"));
		enquiry.setCourseName(formData.get("courseName"));
		
		//sharing the data to view page
		mav.addObject("enquiryDetails", enquiry);
		
		return mav;
	}
	
	@RequestMapping(value="sendEnquiryDetails", method=RequestMethod.POST)
	public String processEnquiry(@ModelAttribute("enquiryForm") Enquiry enquiry,
			                     HttpServletRequest request,
			                     RedirectAttributes redirectAttributes) {
		//service call
		boolean saveEnquiryFlag = enquiryService.saveEnquiryDetails(enquiry);
		
		if(saveEnquiryFlag) {
			//mav.setViewName("confirmation");
			//mav.setViewName("enquiresInfo");
			//mav.addObject("enquiryInfo", enquiryService.getAllEnquires());
			System.out.println("Request Object Hashcode::::" + request.hashCode());
			request.setAttribute("enquiryDetails", enquiry);
			redirectAttributes.addFlashAttribute("enquiryDetails",enquiry);
			return "redirect:acknowledge";
		}else {
			return "enquiryDetails";
		}		
	}
	
	@RequestMapping(value="acknowledge",method=RequestMethod.GET)
	public String getAcknowledgementEnquiry(HttpServletRequest request) {
		System.out.println("Request Object Hashcode-1::::" + request.hashCode());
		System.out.println("Request Information::::" + request.getAttribute("enquiryDetails"));
		return "confirmation";
	}
}

Confirmation.jsp
================
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="ISO-8859-1">
<title>confirmation.jsp</title>
</head>
<body>
   <div style='text-align:center'>
   		<div>Student Name  : <span>${enquiryDetails.name}</span></div>
   		<div>Course Name  : <span>${enquiryDetails.courseName}</span></div>
   		<div>Your Enquiry is Received for above Details Admin Team will connect with you shortly.....</div>
   </div>
</body>
</html>


NOTE
====
1) In Spring MVC We can have option for redirecting the request from one Request Processor method to another request             processor method using redirection mechanism.

2) While redirecting request from one method(Source) to another method(Destination) the shared data is not accessable in        destination method inorder to overcome this problem we can use flash attribute in spring MVC.
   
   Inorder to work with flash attribute as part of Spring MVC we need to use RedirectAttributes interface and contains 
   method as addflashattribute(key,name);

3) If particular request processor method required request and response object means we need to use parameters of 
   request processor method of HttpservletRequest,HttpServletResponse Object.

4) If you execute the above code by submitting data to the form after submission if user refreshing page by using F5 key
   at this time won't create the duplicate records.

   Earlier URL : http://localhost:1234/29_SpringMVC_FormSubmission_App/sendEnquiryDetails >>> Directly get into post request

   
   Present URL : http://localhost:1234/29_SpringMVC_FormSubmission_App/acknowledge  >>> First will get into post request and                                                                                           redirected to get request
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++