Java分页原理

Java分页

常见的分页类型：

• 传统的：采用传统的分页方式，可以明确的获取数据信息，如有多少条数据，分多少页显示等。
• 下拉式：采用下拉式的分页方式，一般无法获取明确的数据数量相关的信息，但在分页操作以后，任然可以看到之前查询的数据。

常见的分页实现方式：

• 使用List接口中的subList(int startIndex, int endIndex)方法实现分页
• 直接使用数据库SQL语句实现分页
• 使用hibernate等框架实现跨数据库的分页

使用subList()实现分页

使用的是List接口中的subList(int startIndex, int endIndex)方法，返回列表中指定的fromIndex（包括）和endIndex（不包括）之间的部分视图。

使用数据库SQL语句实现分页
mysql数据库使用limit关键字，oracle中使用rownum关键字。
例如，从学生表（t_student）中查询出前十条数据
MySql查询语句

select * from t_student limit 0, 10

表示的是从第0条开始取，取10条记录。

PostgreSQL查询语句

select * from t_student limit 10 offset 0

Oracle查询语句

使用hibernate框架实现跨数据库的分页

分页实现方式的比较

实现方式

模型对象

处理映射数据表的对象外，还要创建一个Pager分页对象，其大致的内容如下：

package com.imooc.page.model;

import java.io.Serializable;
import java.util.List;

public class Pager implements Serializable {

    private static final long serialVersionUID = -8741766802354222579L;

    //每页显示多少条记录
    private int pageSize;
    //当前第几页数据
    private int currentPage;
    //一共有多少条记录
    private int totalRecord;
    //一共多少页记录
    private int totalPage;
    //要显示的数据，使用泛型
    private List dataList;

    public Pager() {
        super();
    }

    public Pager(int pageSize, int currentPage, int totalRecord, int totalPage, List dataList) {
        super();
        this.pageSize = pageSize;
        this.currentPage = currentPage;
        this.totalRecord = totalRecord;
        this.totalPage = totalPage;
        this.dataList = dataList;
    }

    public Pager(int pageNum, int pageSize, List sourceList){
        if (sourceList == null){
            return;
        }

        //总记录条数
        this.totalRecord = sourceList.size();
        //每页显示多少条记录
        this.pageSize = pageSize;
        //获取总页数
        this.totalPage = this.totalRecord / this.pageSize;
        if (this.totalRecord % this.pageSize != 0) {
            this.totalPage += 1;
        }

        //当前第几页数据
        this.currentPage = this.totalPage < pageNum ? this.totalPage : pageNum;

        //起始索引
        int fromIndex = this.pageSize * (this.currentPage - 1);
        //结束索引
        int toIndex =this.pageSize * this.currentPage > this.totalRecord ?  this.totalRecord :  this.pageSize * this.currentPage;

        this.dataList = sourceList.subList(fromIndex, toIndex);
    }

    public int getPageSize() {
        return pageSize;
    }
    public void setPageSize(int pageSize) {
        this.pageSize = pageSize;
    }
    public int getCurrentPage() {
        return currentPage;
    }
    public void setCurrentPage(int currentPage) {
        this.currentPage = currentPage;
    }
    public int getTotalRecord() {
        return totalRecord;
    }
    public void setTotalRecord(int totalRecord) {
        this.totalRecord = totalRecord;
    }
    public int getTotalPage() {
        return totalPage;
    }
    public void setTotalPage(int totalPage) {
        this.totalPage = totalPage;
    }
    public List getDataList() {
        return dataList;
    }
    public void setDataList(List dataList) {
        this.dataList = dataList;
    }
    public static long getSerialversionuid() {
        return serialVersionUID;
    }



}

hibernate分页

Dao的实现如下：

package com.imooc.page.dao;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.hibernate.Query;
import org.hibernate.Session;

import com.imooc.page.Constant;
import com.imooc.page.HibernateSessionFactory;
import com.imooc.page.model.Pager;
import com.imooc.page.model.Student;

public class HibernateStudentDaoImpl implements StudentDao{

    @SuppressWarnings("unchecked")
    @Override
    public Pager findStudent(Student searchModel, int pageNum, int pageSize) {
        Pager result = null;

        //存放查询参数
        Map paramMap = new HashMap();

        String stuName = searchModel.getStuName();
        int gender = searchModel.getGender();

        StringBuilder hql = new StringBuilder(" from Student where 1=1");
        StringBuilder countHql = new StringBuilder("select count(id) from Student where 1=1");

        if(stuName != null && !stuName.equals("")){
            hql.append(" and stuName like :stuName");
            countHql.append(" and stuName like :stuName");
            paramMap.put("stuName","%" + stuName + "%");
        }

        if(gender == Constant.GENDER_MALE  || gender == Constant.GENDER_FEMALE){
            hql.append(" and gender = :gender");
            countHql.append(" and gender = :gender");
            paramMap.put("gender",gender);
        }

        //起始索引
        int fromIndex = pageSize * (pageNum - 1);

        List studentList = new ArrayList();

        Session session = null;

        try {

            session = HibernateSessionFactory.getSession();
            //获取query对象
            Query hqlQuery = session.createQuery(hql.toString());
            Query countHqlQuery = session.createQuery(countHql.toString());
            //设置查询参数
            setQueryParams(hqlQuery, paramMap);
            setQueryParams(countHqlQuery, paramMap);

            //从第几条记录开始查询
            hqlQuery.setFirstResult(fromIndex);
            //一共查询多少条记录
            hqlQuery.setMaxResults(pageSize);

            //获取查询的结果
            studentList = hqlQuery.list();
            //获取总计条数
            List countResult = countHqlQuery.list();

            int totalRecord = ((Number)countResult.get(0)).intValue();
            //获取总页数
            int totalPage = totalRecord / pageSize;
            if (totalRecord % pageSize != 0) {
                totalPage += 1;
            }

            //组装pager
            result  = new Pager<>(pageSize, pageNum, totalRecord, totalPage, studentList);


        } catch (Exception e) {
            throw new RuntimeException("查询所有数据异常!", e);
        }finally {
            if (session != null) {
                HibernateSessionFactory.closeSession();
            }
        }

        return result;  
    }

    /**
     * 设置查询参数
     * @param query
     * @param paramMap
     * @return
     */
    private Query setQueryParams(Query query, Map paramMap){
        if(paramMap != null && !paramMap.isEmpty()){
            for(Map.Entry param : paramMap.entrySet()){
                query.setParameter(param.getKey(), param.getValue());
            }
        }
        return query;
    }

}

对应的Servlet如下，这里使用到了fastjson返回json数据：

package com.imooc.page.servlet;

import java.io.IOException;
import java.io.Writer;

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

import com.alibaba.fastjson.JSON;
import com.imooc.page.Constant;
import com.imooc.page.model.Pager;
import com.imooc.page.model.Student;
import com.imooc.page.service.HibernateStudentServiceImpl;
import com.imooc.page.service.StudentService;
import com.imooc.page.util.StringUtil;

public class HibernateDataServlet extends HttpServlet {

    private StudentService studentService = new HibernateStudentServiceImpl();

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

    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // 接收request里的参数
        String stuName = request.getParameter("stuName"); //学生姓名

        // 获取学生性别
        int gender = Constant.DEFAULT_GENDER;
        String genderStr = request.getParameter("gender");
        if(genderStr!=null && !"".equals(genderStr.trim())){
            gender = Integer.parseInt(genderStr);
        }

        // 校验pageNum参数输入合法性
        String pageNumStr = request.getParameter("pageNum"); 
        if(pageNumStr !=null && !StringUtil.isNum(pageNumStr)){
            request.setAttribute("errorMsg", "参数传输错误");
            request.getRequestDispatcher("jdbcSqlStudent.jsp").forward(request, response);
            return;
        }

        int pageNum = Constant.DEFAULT_PAGE_NUM; //显示第几页数据
        if(pageNumStr!=null && !"".equals(pageNumStr.trim())){
            pageNum = Integer.parseInt(pageNumStr);
        }

        int pageSize = Constant.DEFAULT_PAGE_SIZE;  // 每页显示多少条记录
        String pageSizeStr = request.getParameter("pageSize");
        if(pageSizeStr!=null && !"".equals(pageSizeStr.trim())){
            pageSize = Integer.parseInt(pageSizeStr);
        }

        // 组装查询条件
        Student searchModel = new Student(); 
        searchModel.setStuName(stuName);
        searchModel.setGender(gender);

        //调用service 获取查询结果
        Pager result = studentService.findStudent(searchModel, 
                                                                pageNum, pageSize);
        //不使用缓存
        response.setHeader("Cache-Control", "no-cache");  
        response.setHeader("Pragma", "no-cache");  
        //设置超时时间为0
        response.setDateHeader("Expires", 0);  
        //设置编码格式为utf-8
        response.setContentType("text/html;charset=utf-8");

        //获取查询数据的json格式
        String responseStr = JSON.toJSONString(result);
        //写入数据到response
        Writer writer = response.getWriter();
        writer.write(responseStr);
        writer.flush();
    }

    public static void main(String[] args) {
        String s = String.format("%05d", 123);
        System.out.println(s);
    }

}

分页插件

• gbirke/jquery_pagination
• jQuery Pagination plugin Optimized for bootstrap

参考

• Java 分页原理与实践（上）
• Java 分页原理与实践（下）