javaweb paging principle explained in detail

This article examples for you to share javaweb pagination principle specific implementation code, for your reference, the specific content is as follows

public class Page {
 private int currentPage;
 private int totalPage;
 private int count;
 private int PageSize;
 private List<Product> list;
 private String category;
 
 } 

servlet:

package com.learning.web.servlet;

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

import javax.enterprise.inject.New;
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.learning.domain.Page;
import com.learning.domain.Product;
import com.learning.service.ProductService;


@WebServlet("/showProductByPage")
public class ShowProductByPage extends HttpServlet {
 private static final long serialVersionUID = 1L;
 
 
 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  int currentPage=1;
  int pageSize=4;
  // The first 1 Time is empty 
  String currentPageString=request.getParameter("currentPage");
  if (currentPageString!=null) {
  currentPage=Integer.parseInt(currentPageString);
  }
  String category = request.getParameter("category");
  if ("".equals(category)) {
  category=null;
  } 
  ProductService productService=new ProductService();
  Page page=productService.showProductByPage(currentPage,pageSize,category);
  request.setAttribute("page", page);
  request.getRequestDispatcher("/product_list.jsp").forward(request, response);
 }
 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
 doGet(request, response);
 }

}

service:

public Page showProductByPage(int currentPage, int pageSize, String category) {
 try {
  Page page=new Page();
  int count=productDao.count(category);
  page.setCount(count);
  page.setList(productDao.findProductsByPage(currentPage,pageSize,category));
  int totalPage=(int) Math.ceil(1.0*count/pageSize);
  page.setPageSize(pageSize);
  page.setCurrentPage(currentPage);
  page.setTotalPage(totalPage);
  page.setCategory(category);
  return page;
 } catch (SQLException e) {
  e.printStackTrace();
 }
 return null;
 }

Dao:

 public int count(String category) throws SQLException {
 QueryRunner queryRunner=new QueryRunner(C3P0Util.getDataSource());
 String sql=" select count(*) from products ";
 if (category!=null) {
  sql+=" where category='"+category+"'";
 }
 long l= (Long)queryRunner.query(sql, new ScalarHandler(1));
 return (int) l;
 }



 public List<Product> findProductsByPage(int currentPage, int pageSize, String category) throws SQLException {
 QueryRunner queryRunner=new QueryRunner(C3P0Util.getDataSource());
 String sql=" select * from products ";
 if (category!=null) {
  sql+=" where category='"+category+"'";
 }
 sql+=" limit ?,?";
 return queryRunner.query(sql, new BeanListHandler<Product>(Product.class),(currentPage-1)*pageSize,pageSize);
 }