Java分页原理_分页系统原理

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发布于 2022-11-09 08:14:43

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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<T> 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<T> dataList;

    public Pager() {
        super();
    }

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

    public Pager(int pageNum, int pageSize, List<T> 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<T> getDataList() {
        return dataList;
    }
    public void setDataList(List<T> 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<Student> findStudent(Student searchModel, int pageNum, int pageSize) {
Pager<Student> result = null;
//存放查询参数
Map<String, Object> paramMap = new HashMap<String, Object>();
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<Student> studentList = new ArrayList<Student>();
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<String, Object> paramMap){
if(paramMap != null && !paramMap.isEmpty()){
for(Map.Entry<String, Object> 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<Student> 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);
}
}