Javaweb分頁技術實現

分頁技術就是通過SQL語句(如下)來獲取資料，具體實現看下面程式碼

//分頁查詢語句
select * from 表名 where limit page , count;
和
//獲取表中的總資料，確定頁數
select count(*) from 表名;

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1.配置資料來源

在專案的WebContent/META-INF目錄下建立一個context.xml檔案。如圖:

在context.xml檔案中配置：

<Context>      
    <Resource name="jdbc/bookstore" auth="Container"
 
 type="javax.sql.DataSource"
    maxActive="100" maxIdle="30" maxWait="10000"
    username="root" password="root" driverClassName="com.mysql.jdbc.Driver"
    url="jdbc:mysql://localhost:3306/db_bookstore"/>
</Context>

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這裡採用的是Javaweb自帶的DBCP配置，詳細參考Javaweb配置常用的資料來源配置

2.Java程式碼

• 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();
        }
    }
}

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• BookDao

public interface BookDao {

    public List<Book> findBooks(int page , int count) throws SQLException;

    public int count() throws SQLException;
}

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• 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;
    }

}

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• BookService

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

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• 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;
    }
}

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• 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
}

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• Page

public class Page {
    private int currentPage;//當前頁
    private int totalPage;//總頁數
    private int count;//一頁多少條資料
    private List<Book> books;//當前頁的圖書資料
    private int totalCount;//資料總條數
    ...
    //省略get set方法
}

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• 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);
    }

}

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3.jsp程式碼

<%@ 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">
        那些年一起追過的小說
    </font>
    </div>
    <br/>
    <table border="1" width="100%">
            <tr>
                <td>單號</td>
                <td>名稱</td>
                <td>價格</td>
                <td>類別</td>
                <td>作者</td>
                <td>描述</td>
            </tr>

        <c:if test="${empty page.books }">
            <tr>
                <td colspan="8" align="center">沒有商品</td>
            </tr>
        </c:if>
         <c:forEach items="${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=${page.currentPage-1}">上一頁</a>
    </c:if>
        <a href="${pageContext.request.contextPath }/home?page=${1}">首頁</a>
            <c:forEach begin="1" end="${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}">末頁</a>
    <c:if test="${page.currentPage< page.totalPage }">
        <a href="${pageContext.request.contextPath }/home?page=${page.currentPage+1}">下一頁</a>
    </c:if>
    </div>
</body>
</html>

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