简易购物车---分页

最新推荐文章于 2022-08-02 14:32:15 发布

原创最新推荐文章于 2022-08-02 14:32:15 发布 · 931 阅读

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#books #exception #数据库 #sql #integer #object

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这篇博客介绍了如何在Java中实现图书信息的分页功能。首先定义了一个PageBean类，包含当前页码、总页数、每页显示数量等属性。接着创建了BookDAO类，用于与数据库交互，实现分页查询。最后通过Servlet处理HTTP请求，根据当前页码获取图书列表并展示在页面上。

昨天做了获取图书信息的功能，今天呢，来实现分页的功能！
首先要建立个javabean.
public class PageBean {
//当前页的页码
private int currentPage;
//共多少页
private int totalPageNumber;
//当前页需要显示的 List
private List currentPageList;
//共多少条记录
private int totalItemNumer;
//当前页开始的索引
private int fromIndex;
//当前页结束的索引
private int toIndex;
//每页显示多少条记录
private static final int PER_PAGE_ITEM_NUMBER = 8;

//构造器, 接受 currentPage 和 totalItemNumber, 注意 currentPage 前面的 "this"
public PageBean(int currentPage, int totalItemNumer) {
  this.currentPage = currentPage;
  this.totalItemNumer = totalItemNumer;

  //确定共多少页.
  totalPageNumber = totalItemNumer % PER_PAGE_ITEM_NUMBER == 0 ?
    totalItemNumer / PER_PAGE_ITEM_NUMBER : (totalItemNumer / PER_PAGE_ITEM_NUMBER + 1);

  //重新确定当前页的页码, 当前页的页码不能小于 1, 也不能大于 totalPageNumber
  if(currentPage < 1)
   this.currentPage = 1;
  if(currentPage > totalPageNumber)
   this.currentPage = totalPageNumber;

  //确定开始的索引
  fromIndex = (this.currentPage - 1) * PER_PAGE_ITEM_NUMBER;

  //结束结束的索引, 需要判断是不是最后一页
  if(this.currentPage == totalPageNumber){
   toIndex = totalItemNumer;
  }else{
   toIndex = fromIndex + PER_PAGE_ITEM_NUMBER;
  }

  //System.out.println("currentPage: " + currentPage);
  //System.out.println("this.currentPage: " + this.currentPage);
}

public int getCurrentPage() {
return currentPage;
}

public void setCurrentPage(int currentPage) {
this.currentPage = currentPage;
}

public int getTotalPageNumber() {
return totalPageNumber;
}

public void setTotalPageNumber(int totalPageNumber) {
this.totalPageNumber = totalPageNumber;
}

public List getCurrentPageList() {
return currentPageList;
}

public void setCurrentPageList(List currentPageList) {
this.currentPageList = currentPageList;
}

public int getTotalItemNumer() {
return totalItemNumer;
}

public void setTotalItemNumer(int totalItemNumer) {
this.totalItemNumer = totalItemNumer;
}

public int getFromIndex() {
return fromIndex;
}

public void setFromIndex(int fromIndex) {
this.fromIndex = fromIndex;
}

public int getToIndex() {
return toIndex;
}

public void setToIndex(int toIndex) {
  this.toIndex = toIndex;
}
}
2.建立DAO ，与数据库连接.
public class BookDAO {

//分页需要的 queryPerPagePageBean 方法
//sql: SELECT * FROM 表名称 LIMIT M,N --> 从数据库表中 M 条记录开始检索N条记录的语句：
public PageBean queryPerPagePageBean(int currentPageNumber){
  System.out.println("queryPerPagePageBean");

  PageBean pageBean = null;

  //获取 books 表中有多少条记录
  int totalItemNumber = 0;
  totalItemNumber = this.getBookTotalItemNumber();

  pageBean = new PageBean(currentPageNumber, totalItemNumber);

  //查询数据库, 获取当前页需要的 List
  //1. 获取一个数据库连接: 调用 DBHelper.getConnection() 方法
  Connection conn = null;
  conn = DBHelper.getConnection();

  //2. 定义一个 Sql 语句: SELECT id, name, title, price, yr, description, saleAmount FROM books LIMIT m, n
  //2.1 确定 m 的值
  int fromIndex = pageBean.getFromIndex();

  //2.2 确定 n 的值
  int n = pageBean.getToIndex() - pageBean.getFromIndex();

  String sql = "SELECT id, name, title, price, yr, description, saleAmount FROM books LIMIT ?, ?";

  //3. 定义需要传递给 QueryRunner 对象的 query 方法第三个参数的 Object[]
  Object [] params = new Object[]{fromIndex, n};

  //4. 创建 dbutils 中的 QueryRunner 对象
  QueryRunner queryRunner = null;
  queryRunner = new QueryRunner();

  //5. 调用 QueryRunner 对象的 query(Connection, sql, params, new BeanListHandler(Book.class)); 返回一个 List
  //   将返回值赋给 books
  List books = null;
  try {
   books = (List) queryRunner.query(conn, sql, params, new BeanListHandler(Book.class));
  } catch (SQLException e) {
   e.printStackTrace();
   //5.1 若出现异常信息以 RuntimeException 的形式抛出去, 类似于 DBHelper
      //    封装后的异常信息为 MyBookStoreConstants.QUERY_BOOK_LIST_PER_PAGE_EXCEPTION
   throw new RuntimeException(MyBookStoreConstants.QUERY_BOOK_LIST_PER_PAGE_EXCEPTION);
  }

  //6. 为 pageBean 的 currentPageList 属性赋值
  pageBean.setCurrentPageList(books);

  return pageBean;
}

//获取 books 表中有多少条记录
private int getBookTotalItemNumber() {
  int totalItemNumber = 0;

  //1. 获取一个数据库连接: 调用 DBHelper.getConnection() 方法
  Connection conn = DBHelper.getConnection();

  //2. 定义一个 Sql 语句: SELECT count(*) FROM books
  String sql = "SELECT count(*) FROM books";

  //3. 创建 dbutils 中的 QueryRunner 对象
  QueryRunner queryRunner = null;
  queryRunner = new QueryRunner();

  //4. 调用 QueryRunner 对象的 query(Connection, sql, params, new ResultHandler(){}); 返回一个 Integer 对象
  //   将返回值赋给 totalItemNumber
  try {
   totalItemNumber = (Integer) queryRunner.query(conn, sql, new ResultSetHandler(){
    public Object handle(ResultSet resultSet) throws SQLException {
     if(resultSet != null && resultSet.next())
      return resultSet.getInt(1);
     return 0;
    }
   });
  } catch (SQLException e) {
   e.printStackTrace();
   //4.1 若出现异常信息以 RuntimeException 的形式抛出去, 类似于 DBHelper
      //    封装后的异常信息为 MyBookStoreConstants.QUERY_BOOKSTABLE_TOTAL_ITEM_NUMBER_EXCEPTION
   throw new RuntimeException(MyBookStoreConstants.QUERY_BOOKSTABLE_TOTAL_ITEM_NUMBER_EXCEPTION);
  }

  //5. 返回 totalItemNumber
  return totalItemNumber;
}
}
3.建立业务逻辑：实现分页的功能.
这里只是部分代码，而其他的代码，昨天已经写出！
BookService.java
public PageBean getBooksByCurrentPageNumber(int currentPage) {
  BookDAO bookDAO = new BookDAO();
  PageBean pageBean = null;
  pageBean = bookDAO.queryPerPagePageBean(currentPage);

  //3. 返回
  return pageBean;
}
}
4.这是很重要的一步，写Servlet
CatalogPageServlet.java
public class CatalogPageServlet extends HttpServlet {

public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  //分页问题:

  //1. 获取当前页的页码
  String currentPageStr = request.getParameter("currentPage");

  //2. 若 currentPageStr == null, 则应显示第一页
  if(currentPageStr == null)
   currentPageStr = "1";

  int currentPage = Integer.parseInt(currentPageStr);

  //3. 根据跟定的页码值, 获取当前页面使用的 List
  BookService bookService = new BookService();
  //List books = bookService.getBooksByCurrentPageNumber(currentPage);

  PageBean pageBean = bookService.getBooksByCurrentPageNumber(currentPage);

  //4. 派发页面
  String forwardPage = "/WEB-INF/jsp/catalog.jsp";



  request.setAttribute(MyBookStoreConstants.CURRENT_PAGE_PAGE_BEAN, pageBean);

  //4. 派发页面
  RequestDispatcher dispatcher = null;
  dispatcher = request.getRequestDispatcher(forwardPage);
  dispatcher.forward(request, response);
}

}
5.显示页面：catalog.jsp
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<%@ taglib prefix="myBookStore" uri="/WEB-INF/tld/myBookStore.tld" %>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
    <title>My JSP 'catalog.jsp' starting page</title>
    <script type="text/javascript">
    function trunToPage(){
      var pageForm = document.getElementByIdx("pageForm");

   pageForm.submit();
    }
    </script>
</head>

<body>
    <center>
    <c:if test="${requestScope.addToShoppingCartBookTitle != null}">
      <br><br>
      <font color="red">您已经将 ${requestScope.addToShoppingCartBookTitle} 加入到了购物车中</font>
    </c:if>
    <br><br>
    请选择您要购买的书:
    <br><br>
    <table cellpadding="5" cellspacing="0">
      <c:forEach items="${requestScope.currentPagePageBean.currentPageList}" var="book">
       <tr>
        <td>
         <a href="${pageContext.request.contextPath }/bookDetailServlet?bookId=${book.id }&currentPage=${requestScope.currentPagePageBean.currentPage }">${book.title }</a><br>
         ${book.name }
        </td>
        <td>${book.price }</td>
        <td><a href="${pageContext.request.contextPath }/addToShoppingCartServlet?bookId=${book.id }">加入购物车</a></td>
       </tr>
      </c:forEach>
    </table>

    <br><br>

    <form action="catalogPageServlet" id="pageForm">
      当前 ${requestScope.currentPagePageBean.currentPage } / ${requestScope.currentPagePageBean.totalPageNumber } 页   
     <c:if test="${requestScope.currentPagePageBean.currentPage != 1}">
      <a href="catalogPageServlet?currentPage=1">首页</a>   
      <a href="catalogPageServlet?currentPage=${requestScope.currentPagePageBean.currentPage - 1 }">上一页</a>   
     </c:if>

     <c:if test="${requestScope.currentPagePageBean.currentPage != requestScope.currentPagePageBean.totalPageNumber}">
      <a href="catalogPageServlet?currentPage=${requestScope.currentPagePageBean.currentPage + 1 }">下一页</a>   
      <a href="catalogPageServlet?currentPage=${requestScope.currentPagePageBean.totalPageNumber }">末页</a>   
     </c:if>

      转到第 <input type="text" name="currentPage" onchange="trunToPage();" size="2" /> 页
    </form>

    <myBookStore:showCookieBook/>
    </center>
</body>
</html>
    其实呢，分页这个功能模块，在我们的生活中可以体会的到的，只要我们浏览网页的都应该映象很深刻的。最典型的就是淘宝网的网页，你购买的东西的时候，
    购物车内东西放多了，肯定看了不是很舒服，让你一页显示多少条记录，这样让人一目了然，以便查询，查看。
    通过以上一系列的功能实现，对于购物的车的整体有了个清楚的认识，至于购物的车的功能，明天的时候再来实现。