bbs小项目整理（七）（消息分页展现）

分页显示发布的消息形成消息列表

1.首先创建分页的javabean来装载分页的属性设置

在com.congbbs.javabean创建pageBean对象：

package com.congbbs.javabean;


public class PageBean {
    private int currPage; //当前页数
    private int pageSize; //当前显示的记录数
    private int totalCount; //总记录数
    private int tatalPage;  //总页数
    
    public PageBean(){        //无参构造方法
        
    }
    
    public PageBean(int currPage, int pageSize, 
            int totalCount, int tatalPage) {  //有参构造方法
        this.currPage = currPage;
        this.pageSize = pageSize;
        this.totalCount = totalCount;
        this.tatalPage = tatalPage;
    }
    //相应的set和get方法
    public int getCurrPage() {
        return currPage;
    }
    public void setCurrPage(int currPage) {
        this.currPage = currPage;
    }
    public int getPageSize() {
        return pageSize;
    }
    public void setPageSize(int pageSize) {
        this.pageSize = pageSize;
    }
    public int getTotalCount() {
        return totalCount;
    }
    public void setTotalCount(int totalCount) {
        this.totalCount = totalCount;
    }
    public int getTatalPage() {
        return tatalPage;
    }
    public void setTatalPage(int tatalPage) {
        this.tatalPage = tatalPage;
    }
}

分页的思想：通过（mysql的limit语句） 设置查询起点和要查询的记录数将相应的数据从数据库中查询出来，然后再页面上一页页展现出来

　　　　　　要查询出有多少页的数据当然的前提是要计算出有多少记录数啦(总页数 = 总数据记录数/每页记录数)

　　　　　　总记录数通过查询数据库可以得出， 每页记录数由自己设定 ，  当前页由页面传递过来

在上一篇的messageDao中加入相应的方法，在messageDaoImple中对方法进行实现：

package com.congbbs.dao;

import java.util.List;

import com.congbbs.javabean.Message;
import com.congbbs.javabean.PageBean;

public interface MessageDao {
    
    //添加消息
    public void addMessage(Message message);
    
    //分页查询记录数
    public List<Message> findAllMessage(PageBean pageBean);
    
    //获得总记录数
    public int findAllCount();

    
}

package com.congbbs.dao.imple;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.Timestamp;
import java.util.ArrayList;
import java.util.List;

import com.congbbs.dao.MessageDao;
import com.congbbs.javabean.Message;
import com.congbbs.javabean.PageBean;
import com.congbbs.util.DbConn;

public class MessageDaoImpl implements MessageDao {

    //插入一条消息
    @Override
    public void addMessage(Message message) {
        //通过工具类获得数据库的链接
        Connection conn = DbConn.getConnection();
        //编写sql语句
        String sql = "insert into tb_message(messageTitle, messageContent,userID, publishTime)"+
        "values(?,?,?,?)";
        PreparedStatement ps = null;
        try {
            ps = conn.prepareStatement(sql);     //将传过来的数据对应装配到sql语句中
            ps.setString(1, message.getMessageTitle());
            ps.setString(2, message.getMessageContent());
            ps.setInt(3, message.getUserID());
            ps.setTimestamp(4, new Timestamp(message.getPublishTime().getTime()));  // 获取当前操作的时间
            ps.execute();         //将数据提交到数据库中
            
        } catch (Exception e) {
            e.printStackTrace();
        }finally {                //关闭相应的数据连接对象
            DbConn.close(ps);
            DbConn.close(conn);
        }
    }
    //分页查询数据库中的记录
    @Override
    public List<Message> findAllMessage(PageBean pageBean) {
        Connection conn = DbConn.getConnection();
        //将消息按发布时间时间进行排序并分页查询出来
        String findSQL = "select * from tb_message order by publishTime desc limit ?,?";
        PreparedStatement ps = null;
        ResultSet rs = null;
        int pageBegin =  (pageBean.getCurrPage()-1)*pageBean.getPageSize(); //计算每页相应的查询起点
        List<Message> list = new ArrayList<Message>();
        try {
            ps = conn.prepareStatement(findSQL);
            ps.setInt(1, pageBegin);     //设置查询的的起点
            ps.setInt(2, pageBean.getPageSize());   //设置查询的每页记录数
            rs = ps.executeQuery();   //执行查询返回结果集
            while(rs.next()){         //将查询到的数据装配到对象中
                Message message = new Message();
                message.setMessageID(rs.getInt(1));
                message.setMessageTitle(rs.getString(2));
                message.setMessageContent(rs.getString(3));
                message.setUserID(rs.getInt(4));
                message.setPublishTime(rs.getDate(5));
                list.add(message);     //将数据对象装配进list列表中
            }
        } catch (Exception e) {
            e.printStackTrace();
        }finally {      
            DbConn.close(rs);
            DbConn.close(ps);
            DbConn.close(conn);
        }
        return list;
    }
    //查询总记录数
    @Override
    public int findAllCount() {
        Connection conn = DbConn.getConnection(); //获得数据库连接
        String sql = "select count(*) from tb_message";
        int count = 0;   //定义一个计数变量
        PreparedStatement ps = null;
        ResultSet rs = null;
        try {
        ps = conn.prepareStatement(sql);
        rs = ps.executeQuery();
        if(rs.next()){
            count = rs.getInt(1);  //将查询出来的记录数赋给count
        }
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            DbConn.close(rs);
            DbConn.close(ps);
            DbConn.close(conn);
        }
        return count;
    }
}

在com.congbbs.test中编写方法进行测试：

@org.junit.Test
    public void testMessage(){
        MessageDao messageDao = MessageDaoFactory.getMessageDaoInstance();
        int i = messageDao.findAllCount();
        System.out.println("总记录数"+i);
        PageBean pageBean = new PageBean(1, 5, i, i/5);//查询第一页的数据，每页显示五条记录
        List<Message> list=messageDao.findAllMessage(pageBean);
        for (Message message : list) {
            System.out.println(message.getMessageTitle());  // 打印消息的标题
        }
    }

测试成功后就通过servlet来将查询到的数据转发显示在页面上

前台分页页面关键代码如下：

<div align="center">
     <c:if test="${requestScope.pageBean.currPage != 1}">    
        <a href="GetMessageList?currPage=1">首页</a> | 
        <a href="GetMessageList?currPage=${requestScope.pageBean.currPage-1}">上一页</a>
    </c:if>    
    <c:if test="${requestScope.pageBean.currPage!=requestScope.pageBean.tatalPage}">            
        <a href="GetMessageList?currPage=${requestScope.pageBean.currPage+1}">下一页</a> | 
        <a href="GetMessageList?currPage=${requestScope.pageBean.tatalPage}">尾页</a>
    </c:if>    
    当前为第${requestScope.pageBean.currPage}页,共${requestScope.pageBean.tatalPage}页
  </div>

在com.congbbs.servlet中创建GetMessageList的servlet类

package com.congbbs.servlet;

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

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.congbbs.dao.MessageDao;
import com.congbbs.factory.MessageDaoFactory;
import com.congbbs.javabean.Message;
import com.congbbs.javabean.PageBean;

public class GetMessageList extends HttpServlet {
    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doPost(request, response);
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setCharacterEncoding("UTF-8");
        response.setContentType("text/html; charset=UTF-8");
        int currentPage = 0; //定义当前页
        String currentPageStr = request.getParameter("currPage"); //从界面获取当前页
        if(currentPageStr == null || "".equals(currentPageStr)){  //没有传值当前页则设置为默认的第一页
            currentPage = 1;
        }else{
            currentPage = Integer.parseInt(currentPageStr);  //将获得的当前页字串转为int
        }
        MessageDao messageDao = MessageDaoFactory.getMessageDaoInstance();  //获得message业务逻辑实例
        int totalCount = messageDao.findAllCount();  //查询总记录数
        int totalPage = 0;
        int pageSize = 5;  //定义每页显示的记录数
        if(totalCount%pageSize == 0){   //总页数的计算方法整除无余数
            totalPage = totalCount/pageSize; //直接设为总页数
        }else{                         //无法整除页数加一
            totalPage = totalCount/pageSize + 1;
        }
        PageBean pageBean = new PageBean(currentPage, pageSize,totalCount, totalPage);
        List<Message> messages = messageDao.findAllMessage(pageBean);
        request.setAttribute("messages", messages);  //将查询的数据传到request域中
        request.setAttribute("pageBean", pageBean);  //将分页信息传到request域中
        ServletContext servletContext = getServletContext(); 
        RequestDispatcher dispatcher = servletContext
                .getRequestDispatcher("/jsp/messageList.jsp"); //转到消息列表显示界面
        dispatcher.forward(request, response);
    }

}

到此分页的显示消息列表的功能也完成了