controller in MVC - servlet

MVC concept

image.png

从model 到 controller

// step 1: get the student data from helper class (model)
List students = StudentDataUtil.getStudents();

// step 2: add students to request object
request.setAttribute("student_list", students);

• 从model取得数据，放入request中
• 这里就是从自己写的类里面读了数据出来，使用setAttribute放入数据到request中。

从controller 到 view

• RequestDispatcher

RequestDispatcher dispatcher = 
                request.getRequestDispatcher("view_students_two.jsp");        

这个dispatcher就是作为一个wrapper来封装服务器端文件（如servlet, JSP file, or HTML file）。
getRequestDispatcher的参数用来定位文件位置。
这里是封装了jsp文件，位于view_students_two.jsp。

• forward method

dispatcher.forward(request, response);

这个forward就是起传递作用，将request从servlet传递到服务器的其它文件（如servlet, JSP file, or HTML file）。
这里就是将request传递给了jsp, 目的达到。

package com.luv2code.servletdemo.mvctwo;

import java.io.IOException;
import java.util.List;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
* Servlet implementation class MvcDemoServletTwo
*/
@WebServlet("/MvcDemoServletTwo")
public class MvcDemoServletTwo extends HttpServlet {
   private static final long serialVersionUID = 1L;
      
   /**
    * @see HttpServlet#HttpServlet()
    */
   public MvcDemoServletTwo() {
       super();
       // TODO Auto-generated constructor stub
   }

   /**
    * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
    */
   protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

       // step 1: get the student data from helper class (model)
       List students = StudentDataUtil.getStudents();
       
       // step 2: add students to request object
       request.setAttribute("student_list", students);
       
       // step 3: get request dispatcher
       RequestDispatcher dispatcher = 
               request.getRequestDispatcher("view_students_two.jsp");      
       
       // step 4: now forward to JSP
       dispatcher.forward(request, response);
   }

   
   
   
   
   
   
   
   
   
   /**
    * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
    */
   protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
       // TODO Auto-generated method stub
       doGet(request, response);
   }

}

package com.luv2code.servletdemo.mvctwo;

import java.io.IOException;
import java.util.List;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
* Servlet implementation class MvcDemoServletTwo
*/
@WebServlet("/MvcDemoServletTwo")
public class MvcDemoServletTwo extends HttpServlet {
   private static final long serialVersionUID = 1L;
      
   /**
    * @see HttpServlet#HttpServlet()
    */
   public MvcDemoServletTwo() {
       super();
       // TODO Auto-generated constructor stub
   }

   /**
    * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
    */
   protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

       // step 1: get the student data from helper class (model)
       List students = StudentDataUtil.getStudents();
       
       // step 2: add students to request object
       request.setAttribute("student_list", students);
       
       // step 3: get request dispatcher
       RequestDispatcher dispatcher = 
               request.getRequestDispatcher("view_students_two.jsp");      
       
       // step 4: now forward to JSP
       dispatcher.forward(request, response);
   }

   
   
   /**
    * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
    */
   protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
       // TODO Auto-generated method stub
       doGet(request, response);
   }

}

Reference
https://docs.oracle.com/javaee/7/api/javax/servlet/RequestDispatcher.html