Javaweb分页技术实现

心已赠人 2022-07-05 15:01 375阅读 0赞

## Javaweb分页技术实现 ##

分页技术就是通过SQL语句(如下)来获取数据，具体实现看下面代码

//分页查询语句
    select * from 表名 where limit page , count;
    和
    //获取表中的总数据，确定页数
    select count(*) from 表名;

### 1.配置数据源 ###

在项目的WebContent/META-INF目录下创建一个context.xml文件。如图:

![image][]

在context.xml文件中配置：

这里采用的是Javaweb自带的DBCP配置，详细参考Javaweb配置常用的数据源配置

### 2.Java代码 ###

*  DBUtil

public class DBUtils {
    
        public static Connection getConn(){
            try {
                InitialContext context = new InitialContext();
                DataSource dataSource = (DataSource) context.lookup("java:/comp/env/jdbc/bookstore");
                return dataSource.getConnection();
            } catch (SQLException e) {
                e.printStackTrace();
            } catch (NamingException e) {
                e.printStackTrace();
            }
            return null;
        }
    
        public static void close(Connection conn){
            try {
                if(conn!=null){
                    conn.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }

*  BookDao

public interface BookDao { 
    
        public List<Book> findBooks(int page , int count) throws SQLException;
    
        public int count() throws SQLException;
    }

*  BookDaoImpl

public class BookDaoImpl implements BookDao{ 
    
        private Connection conn = DBUtils.getConn();
    
        @Override
        public List<Book> findBooks(int page, int count) throws SQLException {
    
            if(conn==null){
                throw new NullPointerException("conn is null");
            }
            PreparedStatement ps = conn.prepareStatement("SELECT id,name,price,category,author,descs FROM tb_bookstore LIMIT ?,?");
            if(ps==null){
                throw new NullPointerException("ps is null");
            }
            ps.setInt(1, (page-1)*count);
            ps.setInt(2, count);
            ResultSet rs = ps.executeQuery();
    
            if(rs==null){
                throw new NullPointerException("rs is null");
            }   
            List<Book> books = new ArrayList<>();
            while (rs.next()) {
                Book book = new Book();
                book.setId(rs.getInt(1));
                book.setName(rs.getString(2));
                book.setPrice(rs.getDouble(3));
                book.setCategory(rs.getString(4));
                book.setAuthor(rs.getString(5));
                book.setDescs(rs.getString(6));
                books.add(book);
            }   
            return books;
        }
    
        @Override
        public int count() throws SQLException {
            if(conn==null){
                throw new NullPointerException("conn is null");
            }
            PreparedStatement ps = conn.prepareStatement("SELECT COUNT(*) FROM tb_bookstore");
            if(ps==null){
                throw new NullPointerException("ps is null");
            }
            ResultSet rs = ps.executeQuery();
    
            if(rs==null){
                throw new NullPointerException("rs is null");
            }   
            int count = 0;
            if (rs.next()) {
                count = rs.getInt(1);
            }
            return count;
        }
    
    }

*  BookService

public interface BookService {
        public Page findPage(int page,int count);
    }

*  BookServiceImpl

package com.yundoku.service.impl;
    
    import java.sql.SQLException;
    import java.util.List;
    import com.yundoku.dao.BookDao;
    import com.yundoku.dao.impl.BookDaoImpl;
    import com.yundoku.domain.Book;
    import com.yundoku.domain.Page;
    import com.yundoku.service.BookService;
    
    public class BookServiceImpl implements BookService{ 
    
        private BookDao bookDao = new BookDaoImpl();
    
        @Override
        public Page findPage(int page, int count) {
            if(bookDao==null){
                bookDao = new BookDaoImpl();
            }
            try {
                List<Book> books = bookDao.findBooks(page, count);
                System.out.println(books);
                int totle = bookDao.count();
                System.out.println(totle);
                Page p = new Page();
                p.setBooks(books);
                p.setCurrentPage(page);
                p.setCount(count);
                p.setTotalCount(totle);
                int totlePage = totle%count==0?totle/count:(totle/count)+1;
                p.setTotalPage(totlePage);
                return p;
            } catch (SQLException e) {
                e.printStackTrace();
            }
            return null;
        }
    }

*  Book

public class Book {
    
        private int id;
        private String name;
        private double price;
        private String category;
        private String author;
        private String descs;
        ...
        //省略get set方法
    }

*  Page

public class Page {
        private int currentPage;//当前页
        private int totalPage;//总页数
        private int count;//一页多少条数据
        private List<Book> books;//当前页的图书数据
        private int totalCount;//数据总条数
        ...
        //省略get set方法
    }

*  HomeServlet

@WebServlet({ "/HomeServlet", "/home" })
    public class HomeServlet extends HttpServlet { 
        private static final long serialVersionUID = 1L;
    
        public HomeServlet() {
            super();
        }
    
        protected void doGet(HttpServletRequest request, HttpServletResponse response)
                throws ServletException, IOException {
    
            request.setCharacterEncoding("utf-8");
            response.setContentType("text/html;charset=utf-8");   
    
            BookService service = new BookServiceImpl();
            int currentPage=1;
            int count=10;
            String value = request.getParameter("page");
            if(value!=null&&!"".equals(value)){         
                currentPage = Integer.parseInt(value);
            }
    
            Page page  = service.findPage(currentPage, count);
            request.setAttribute("page", page);
            request.getRequestDispatcher("/jsp/home.jsp?page="+currentPage).forward(request, response); 
    
        }
    
        protected void doPost(HttpServletRequest request, HttpServletResponse response)
                throws ServletException, IOException {
            doGet(request, response);
        }
    
    }

### 3.jsp代码 ###

<%@ page language="java" contentType="text/html; charset=utf-8" pageEncoding="utf-8" isELIgnored="false"%>
    <%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
    <html>
    <head>
    <title>Insert title here</title>
    </head>
    <body>
    
        <div align="center" >
        <font size="5">
            那些年一起追过的小说
        </font>
        </div>
        <br/>
        <table border="1" width="100%">
                <tr>
                    <td>单号</td>
                    <td>名称</td>
                    <td>价格</td>
                    <td>类别</td>
                    <td>作者</td>
                    <td>描述</td>
                </tr>
    
            <c:if test="${empty page.books }">
                <tr>
                    <td colspan="8" align="center">没有商品</td>
                </tr>
            </c:if>
             <c:forEach items="${page.books }" var="book">
                <tr>
                    <td>${book.id}</td>
                    <td>${book.name}</td>
                    <td>${book.price}</td>
                    <td>${book.category}</td>
                    <td>${book.author}</td>
                    <td>${book.descs}</td>
                </tr>
            </c:forEach>
    
        </table>
        <br/>
        <div align="center">
        <c:if test="${page.currentPage>1 }">
            <a href="${pageContext.request.contextPath }/home?page=${page.currentPage-1}">上一页</a>
        </c:if>
            <a href="${pageContext.request.contextPath }/home?page=${1}">首页</a>
                <c:forEach begin="1" end="${page.totalPage }" step="1" var="i">
                    <c:if test="${page.currentPage==i }">
                        <a href="${pageContext.request.contextPath }/home?page=${i}"><font color="#ff0000">${i}</font></a>
                    </c:if>
                    <c:if test="${page.currentPage!=i }">
                        <a href="${pageContext.request.contextPath }/home?page=${i}">${i}</a>
                    </c:if>
                </c:forEach>
            <a href="${pageContext.request.contextPath }/home?page=${page.totalPage}">末页</a>
        <c:if test="${page.currentPage< page.totalPage }">
            <a href="${pageContext.request.contextPath }/home?page=${page.currentPage+1}">下一页</a>
        </c:if>
        </div>
    </body>
    </html>

![image][image 1]

[image]: http://oe9ggtbcb.bkt.clouddn.com/%25KMW%28Q0%5D%600%7BX9IVZ%259W0MMR.png
[image 1]: http://oe9ggtbcb.bkt.clouddn.com/QQ%E5%9B%BE%E7%89%8720170324213042.png