分页查询

Page.java

package com.imooc.entity;

/**
 * 分页对应的实体类
 */
public class Page {
    /**
     * 总条数
     */
    private int totalNumber;
    /**
     * 当前第几页
     */
    private int currentPage;
    /**
     * 总页数
     */
    private int totalPage;
    /**
     * 每页显示条数
     */
    private int pageNumber = 5;
    /**
     * 数据库中limit的参数，从第几条开始取
     */
    private int dbIndex;
    /**
     * 数据库中limit的参数，一共取多少条
     */
    private int dbNumber;
    
    /**
     * 根据当前对象中属性值计算并设置相关属性值
     */
    public void count() {
        // 计算总页数
        int totalPageTemp = this.totalNumber / this.pageNumber;
        int plus = (this.totalNumber % this.pageNumber) == 0 ? 0 : 1;
        totalPageTemp = totalPageTemp + plus;
        if(totalPageTemp <= 0) {
            totalPageTemp = 1;
        }
        this.totalPage = totalPageTemp;
        
        // 设置当前页数
        // 总页数小于当前页数，应将当前页数设置为总页数
        if(this.totalPage < this.currentPage) {
            this.currentPage = this.totalPage;
        }
        // 当前页数小于1设置为1
        if(this.currentPage < 1) {
            this.currentPage = 1;
        }
        
        // 设置limit的参数
        this.dbIndex = (this.currentPage - 1) * this.pageNumber;
        this.dbNumber = this.pageNumber;
    }

    public int getTotalNumber() {
        return totalNumber;
    }

    public void setTotalNumber(int totalNumber) {
        this.totalNumber = totalNumber;
        this.count();
    }

    public int getCurrentPage() {
        return currentPage;
    }

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

    public int getTotalPage() {
        return totalPage;
    }

    public void setTotalPage(int totalPage) {
        this.totalPage = totalPage;
    }

    public int getPageNumber() {
        return pageNumber;
    }

    public void setPageNumber(int pageNumber) {
        this.pageNumber = pageNumber;
        this.count();
    }

    public int getDbIndex() {
        return dbIndex;
    }

    public void setDbIndex(int dbIndex) {
        this.dbIndex = dbIndex;
    }

    public int getDbNumber() {
        return dbNumber;
    }

    public void setDbNumber(int dbNumber) {
        this.dbNumber = dbNumber;
    }
}

xml

  <select id="queryMessageListByPage" parameterType="java.util.Map" resultMap="MessageResult">
    select <include refid="columns"/> from MESSAGE
    <where>
        <if test="message.command != null and !&quot;&quot;.equals(message.command.trim())">
            and COMMAND=#{message.command}
        </if>
        <if test="message.description != null and !&quot;&quot;.equals(message.description.trim())">
            and DESCRIPTION like '%' #{message.description} '%'
        </if>
    </where>
    order by ID LIMIT #{page.dbIndex},#{page.dbNumber}
  </select>

dao

    public List<Message> queryMessageListByPage(Map<String,Object> parameter) {
        DBAccess dbAccess = new DBAccess();
        List<Message> messageList = new ArrayList<Message>();
        SqlSession sqlSession = null;
        try {
            sqlSession = dbAccess.getSqlSession();
            // 通过sqlSession执行SQL语句
            IMessage imessage = sqlSession.getMapper(IMessage.class);
            messageList = imessage.queryMessageListByPage(parameter);
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            if(sqlSession != null) {
                sqlSession.close();
            }
        }
        return messageList;
    }

servlet

package com.imooc.servlet;

import java.io.IOException;
import java.util.regex.Pattern;

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

import com.imooc.entity.Page;
import com.imooc.service.QueryService;

/**
 * 列表页面初始化和查询控制
 */
@SuppressWarnings("serial")
public class ListServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        // 设置编码
        req.setCharacterEncoding("UTF-8");
        // 接受页面的值
        String command = req.getParameter("command");
        String description = req.getParameter("description");
        String currentPage = req.getParameter("currentPage");
        // 创建分页对象
        Page page = new Page();
        Pattern pattern = Pattern.compile("[0-9]{1,9}");
        if(currentPage == null ||  !pattern.matcher(currentPage).matches()) {
            page.setCurrentPage(1);
        } else {
            page.setCurrentPage(Integer.valueOf(currentPage));
        }
        QueryService listService = new QueryService();
        // 查询消息列表并传给页面
        req.setAttribute("messageList", listService.queryMessageListByPage(command, description,page));
        // 向页面传值
        req.setAttribute("command", command);
        req.setAttribute("description", description);
        req.setAttribute("page", page);
        // 向页面跳转
        req.getRequestDispatcher("/WEB-INF/jsp/back/list.jsp").forward(req, resp);
    }
    
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        this.doGet(req, resp);
    }
}