Front system four: display page display: create Controller class; (Controller part of paging module)

table of Contents

I. Overview

Two: Create the Controller part

As a result, the controller part and the model part are developed; the next task is to get the value in the View and render it;

---

I. Overview

This part is mainly the Controller layer part of the MVC architecture:

      (1) The Controller in MVC plays the role of connecting the previous and the next, which is used to accept parameters, call business logic, and return the result of the processing;

     (2) MVC architecture pattern, in JavaWeb, Servlet is usually used as Controller;

      (3) In Java development, the controller (Controller) is generally a class of ***Controller;

---

Two: Create the Controller part

Under the controller package, create the Servlet class PaintingController: 

package com.imooc.mgallery.controller;

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

import com.imooc.mgallery.service.PaintingService;
import com.imooc.mgallery.utils.PageModel;

/**
 * Servlet implementation class PaintingController
 */
@WebServlet("/page")
public class PaintingController extends HttpServlet {
	private static final long serialVersionUID = 1L;
	// 因为在Controller中，需要调用Service，所以这儿先创建PaintingService类的对象；
	private PaintingService paintingService = new PaintingService();
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public PaintingController() {
        super();
        // TODO Auto-generated constructor stub
    }

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		// 1.接受HTTP请求的参数
		String page = request.getParameter("p");
		String rows = request.getParameter("r");
		if(page == null) {    // 如果前台请求的时候没有附带“p”和“r”两个参数，那么page和rows都会是空的，
			page = "1";       // 这样下面的paintingService.pagination()会报空指针异常；所以这儿判断处理一下；
		}                      // 如果page或者rows为空，就给其附一个默认值；
		if(rows == null) {
			rows = "6";
		}
		// 2.调用Service方法，得到处理结果；
		PageModel pageModel = paintingService.pagination(Integer.parseInt(page), Integer.parseInt(rows));
		// 3.将结果放在当前的请求属性中；
		request.setAttribute("pageModel", pageModel);  // 这儿的pageModel必须是一个标准的javaBean，这样才能被前台的JSP的el表达式等识别获取
		// 4.请求转发至对应的JSP（view视图），进行数据展现；
		// 使用请求转发，将当前的请求转发到inde.jsp上；这儿的视图放在了/WEB-INF/jsp目录下；
		request.getRequestDispatcher("/WEB-INF/jsp/index.jsp").forward(request, response);
	}

}

A few explanations of the PaintingController class:

      (1) In JavaWeb, the Servlet class is generally used as the implementation class of Controller;

      (2) The Controller class is generally ***Controller; (there is no Servlet in the class name)

      (3) The result obtained by calling the Service is set as the requested attribute; to facilitate identification and acquisition such as the el expression of JSP;

      (4) The result obtained by calling Service needs to be a standard JavaBean, so as to facilitate the identification and acquisition of el expressions such as JSP;

      (5) This Servlet implements [query], so only the doget() method is retained;

---

As a result, the controller part and the model part are developed; the next task is to get the value in the View and render it;