数据库分页技术

1、数据库分页技术的基本思想：
    (1)、确定记录跨度。即确定每页显示数据的条数。    
    (2)、获取记录总数。即获取要显示在页面中的总记录数。其目的是依据总记录数来技术得到总页数。
    (3)、确定分页后的总页数。依据公式“总记录数/跨度”计算分页后的总页数。要注意的是：如果总页数有余数，要去掉余数，将总页数加1。修改为:（总记录数-1）/跨度+1
    (4)、根据当前页数显示数据。注意：如果该页数小于1，则使其等于1；如果页数大于最大页数，则使其等于最大页数。
    (5)、通过For循环语句分页显示数据。
2、使用标准的SQL语句实现数据分页：
    (1)、获取前n条数据：
            SELECT TOP n[PERCENT] *
            FROM TABLE
            WHERE ......
            ORDER BY......
    (2)、获取分页数据：
            在java中通过参数来获取分页数据：
            String sql="select top "+pageSize+"* from table where id not in (select top"+(page-1)*pageSize+" id from table order by id ASC ) order by id ASC";
            其中：
                        pageSize：英语指定分页后每页显示的数据
                        page:用于指定当前页数
3、MySQL数据库分页：
        MySQL数据库提供了LIMIT函数课一方便实现分页：
            SELECT [DISTINCT|UNIQUE]( *,columname [as alias])
            FROM TABLE
            WHERE ......
            ORDER BY......
            LIMIT [offset],rows
            eg:
                   String strSql = "select * from tb_orderform order by id limit "+(page-1)*pagesize+","+pagesize+""; 
4、Hibernate分页：
        Hibernate对分页也提供了很好的支持，可以利用HQL和QBC检索方式实现数据分页。
        eg:从索引位置3开始的6条记录。
                 (1)、HQL方式：
                            Query query=session.createQuery("from User");
                            query.setFirstResult(3);
                            query.setMaxResult(6);
                 (2)、QBC方式：
                            Criteria criteria=session.createCriteria(User.class);
                            createria.setFirstResult(3);
                            createria.setMaxResult(6);
5、实践：
             (1)、实体类：

 1 package  com.domain;
 2
 3 import  org.apache.struts.action.ActionForm;
 4
 5 public   class  PeopleForm  extends  ActionForm  {
 6    private int id;
 7    private String name;
 8    private String sex ;
 9    private int age;
10    private String job;
11    public int getId() {
12        return id;
13    }
14    public void setId(int id) {
15        this.id = id;
16    }
17    public String getName() {
18        return name;
19    }
20    public void setName(String name) {
21        this.name = name;
22    }
23    public String getSex() {
24        return sex;
25    }
26    public void setSex(String sex) {
27        this.sex = sex;
28    }
29    public int getAge() {
30        return age;
31    }
32    public void setAge(int age) {
33        this.age = age;
34    }
35    public String getJob() {
36        return job;
37    }
38    public void setJob(String job) {
39        this.job = job;
40    }
41   
42 
43}
44

 

            (2)、Dao:
                    数据库操作：

 

 1 package  com.dao;
 2 import  java.sql. * ;
 3 public   class  JDBConnection  {  
 4Connection connection = null;    
 5static {
 6    try {
 7        Class.forName("com.mysql.jdbc.Driver"); // 静态块中实现加载数据库驱动
 8    } catch (ClassNotFoundException e) {
 9        e.printStackTrace();
10    }
11}    
12public Connection creatConnection(){
13        //创建数据库连接对象
14    String url = "jdbc:mysql://localhost:3306/db_database20";    //指定数据库连接URL
15    String userName = "root";            //连接数据库用户名
16    String passWord = "111";            //连接数据库密码
17    try {
18        connection = DriverManager.getConnection(url,userName, passWord);    //获取数据库连接    
19    } catch (SQLException e) {        
20        e.printStackTrace();
21    }
22    return connection;
23}
24    //对数据库的查询操作
25public ResultSet executeQuery(String sql) {
26    ResultSet rs;            //定义查询结果集
27    try {
28        if (connection == null) {
29            creatConnection();    //创建数据库连接
30        }
31        Statement stmt = connection.createStatement();    //创建Statement对象      
32        rs = stmt.executeQuery(sql);            //执行查询SQL语句      
33    } catch (SQLException e) {
34        System.out.println(e.getMessage());           
35        return null;            //有异常发生返回null
36    }
37    return rs;                    //返回查询结果集对象
38}
39//关闭数据库连接
40public void closeConnection() {
41    if (connection != null) {        //如果Connection对象
42        try {
43            connection.close();        //关闭连接
44        } catch (SQLException e) {
45            e.printStackTrace();
46        } finally {
47            connection = null;
48        }
49    }
50}
51
52}
53

            业务逻辑：      

 1 package  com.dao;
 2 import  java.util. * ;
 3 import  com.domain.PeopleForm;
 4 import  java.sql.ResultSet;
 5 import  java.sql. * ;
 6 public   class  PeopleDao  {
 7    private JDBConnection connection = null;
 8    public PeopleDao() {
 9        connection = new JDBConnection();
10    }
11    //查询所有员工信息方法
12public List selectPeople() {
13    List list = new ArrayList();        //创建保存查询结果集集合对象
14    PeopleForm form = null;
15    String sql = "select * from tb_emp";    //定义查询tb_emp表中全部数据SQL语句
16    ResultSet rs = connection.executeQuery(sql);    //执行查询
17    try {
18        while (rs.next()) {                //循环遍历查询结果集
19            form = new PeopleForm();    //创建ActionForm实例
20            form.setId(Integer.valueOf(rs.getString(1)));    //获取查询结果
21            form.setName(rs.getString(2));
22            form.setSex(rs.getString(3));
23            form.setAge(rs.getInt(4));
24            form.setJob(rs.getString(5));
25            list.add(form);                //向集合中添加对象
26        }
27    } catch (SQLException ex) {
28    }
29    connection.closeConnection();        //关闭数据连接
30    return list;                        //返回查询结果
31}
32}
33

            (3)Action:          

 

 1 package  com.action;
 2
 3 import  org.apache.struts.action. * ;
 4 import  javax.servlet.http. * ;
 5 import  com.dao.PeopleDao;
 6 import  java.util.List;
 7 public   class  PeopleAction  extends  Action  {
 8private PeopleDao dao = null;
 9public ActionForward execute(ActionMapping mapping, ActionForm form,
10        HttpServletRequest request, HttpServletResponse response) {
11    dao = new PeopleDao(); // 创建保存有数据查询类对象
12    List list = dao.selectPeople(); // 调用数据查询方法
13    int pageNumber = list.size(); // 计算出有多少条记录
14    int maxPage = pageNumber; // 计算有多少页数
15    String number = request.getParameter("i"); // 获取保存在request对象中变量
16    if (maxPage % 4 == 0) { // “4”代表每页显示有4条记录
17        maxPage = maxPage / 4; // 计算总页数
18    } else { // 如果总页数除以4不整除
19        maxPage = maxPage / 4 + 1; // 将总页数加1
20    }
21    if (number == null) { // 如果保存在request范围内的当前页数为null
22        number = "0"; // 将number为0
23    }
24    request.setAttribute("number", String.valueOf((number))); // 将number保存在request范围内
25    request.setAttribute("maxPage", String.valueOf(maxPage)); // 将分的总页数保存在request范围内
26    int nonce = Integer.parseInt(number) + 1;
27    request.setAttribute("nonce", String.valueOf(nonce));
28    request.setAttribute("pageNumber", String.valueOf(pageNumber));
29    request.setAttribute("list", list);
30    return mapping.findForward("peopleAction"); // 请求转发地址
31}
32}
33

                 (4)、页面代码：

index.jsp:
<% @ page language = " java "   import = " java.util.* "  pageEncoding = " gbk " %>
<%
String path  =  request.getContextPath();
String basePath  =  request.getScheme() + " :// " + request.getServerName() + " : " + request.getServerPort() + path + " / " ;
%>
<! DOCTYPE HTML PUBLIC  " -//W3C//DTD HTML 4.01 Transitional//EN " >
< html >
   < head >
     < base href = " <%=basePath%> " >     
     < title > My JSP  ' index.jsp '  starting page </ title >
     < meta http - equiv = " pragma "  content = " no-cache " >
     < meta http - equiv = " cache-control "  content = " no-cache " >
     < meta http - equiv = " expires "  content = " 0 " >     
     < meta http - equiv = " keywords "  content = " keyword1,keyword2,keyword3 " >
     < meta http - equiv = " description "  content = " This is my page " >
     < meta http - equiv = " refresh "  content = " 0;URL=peopleAction.do " >
   </ head >   
   < body >
   
   </ body >
</ html >

===============================================
pagenation.jsp
<% @ page contentType = " text/html; charset=gbk "   %>
<% @page  import = " java.sql.* " %>
<% @page  import = " java.util.* " %>
<% @page  import = " com.domain.PeopleForm " %>
< html >
< meta http - equiv = " Content-Type "  content = " text/html;charset=gbk " >
<% @ taglib uri = " /WEB-INF/struts-bean.tld "  prefix = " bean " %>
<% @ taglib uri = " /WEB-INF/struts-html.tld "  prefix = " html " %>
<% @ taglib uri = " /WEB-INF/struts-logic.tld "  prefix = " logic " %>
< link href = " css/style.css "  rel = " stylesheet "  type = " text/css " >
<%
  List list  =  (List)request.getAttribute( " list " );             // 获取保存在request范围内的数据
   int  number  =  Integer.parseInt((String)request.getAttribute( " number " )); 
   int  maxPage  =  Integer.parseInt((String)request.getAttribute( " maxPage " ));
   int  pageNumber  =  Integer.parseInt((String)request.getAttribute( " pageNumber " ));
   int  start  =  number * 4 ; // 开始条数
   int  over  =  (number + 1 ) * 4 ; // 结束条数
   int  count = pageNumber - over; // 还剩多少条记录
   if (count <= 0 ) {
  over=pageNumber;
  }  
%>
< head >
< title > 利用查询结果集进行分页 </ title >
</ head >
< body  >
   < table width = " 756 "  height = " 650 "  border = " 0 "  align = " center "  cellpadding = " 0 "  
  cellspacing = " 0 "   >    
     < tr >
       < td height = " 280 " >
         < table width = " 635 "  border = " 1 "  align = " center " >
     < tr align = " center "  bgcolor = " #FFFFFF " >
       < td width = " 112 "  height = " 17 " >< span  class = " style4 " > 编号 </ span ></ td >
       < td width = " 112 " >< span  class = " style4 " > 姓名 </ span ></ td >
       < td width = " 112 " >< span  class = " style4 " > 性别 </ span ></ td >
       < td width = " 112 " >< span  class = " style4 " > 年龄 </ span ></ td >
       < td width = " 142 " >< span  class = " style4 " > 职位 </ span ></ td >
     </ tr >    
     < logic:iterate id = " element "  indexId = " index "  name = " list "  
      offset = " <%=String.valueOf(start)%> "  
      length = " 4 " >                 <!--  通过迭代标签将员工信息输出  -->
     < tr align = " center "  bgcolor = " #FFFFFF " >
       < td height = " 22 " >
       < bean:write name = " element "  property = " id " />
       </ td >
       < td >
       < bean:write name = " element "  property = " name " />
      </ td >
       < td >< bean:write name = " element "  property = " sex " />
       </ td >
       < td >< bean:write name = " element "  property = " age " /> 岁 </ td >
       < td >< bean:write name = " element "  property = " job " />
  </ td >
     </ tr >
    </ logic:iterate >
   </ table >
    </ td >
     </ tr >
     < tr >
       < td valign = " top " >
< form name = " form "  method = " post "  action = " peopleAction.do " >  
< table width = " 400 "  height = " 20 "  border = " 0 "  align = " center "  cellpadding = " 0 "  cellspacing = " 0 " >
      < tr >           
        < td width = " 400 "  valign = " middle "  bgcolor = " #CCCCCC " >& nbsp; & nbsp;
           共为 < bean:write name = " maxPage " />      <!--  输出总记录数  -->
           页 & nbsp; 共有 < bean:write name = " pageNumber " />       <!--  输出总分页  -->          
           条 & nbsp; 当前为第 < bean:write name = " nonce " /> 页  & nbsp;     <!--  输出当前页数  -->
            < logic:equal name = " nonce "  value = " 1 " >
             首页
            </ logic:equal >               
            < logic:notEqual name = " nonce "  value = " 1 " >      <!--  如果当前页码不等于1  -->
               < a href = " peopleAction.do?i=0 " > 首页 </ a >      <!--  提供首页超链接  -->
            </ logic:notEqual >
             & nbsp;
         < logic:lessEqual name = " maxPage "  value = " ${nonce} " >      <!--  如果当前页码不小于总页数  -->
            尾页                                 <!--  不提供尾页超链接  -->
         </ logic:lessEqual >
         < logic:greaterThan name = " maxPage "   value = " ${nonce} " >   <!--  如果当前页码小于总页数  -->
         < a href = " peopleAction.do?i=<%=maxPage-1%> " > 尾页 </ a >& nbsp;    <!--  提供尾页超链接  -->
         </ logic:greaterThan >   
         < logic:equal name = " nonce "   value = " 1 " >      <!--  如果当前页码等于1  -->
             上一页                                 <!--  不提供上一页超链接  -->
          </ logic:equal >
          < logic:notEqual name = " nonce "   value = " 1 " >      <!--  如果当前页码不等于1  -->
              < a href = " peopleAction.do?i=<%=number-1%> " > 上一页 </ a >     <!--  提供上一页超链接  -->
          </ logic:notEqual >
         < logic:lessEqual name = " maxPage "  value = " ${nonce} " >  
            下一页
         </ logic:lessEqual >
             < logic:greaterThan name = " maxPage "  value = " ${nonce} " >      <!--  如果当前页面小于总页数  -->
                 < a href = " peopleAction.do?i=<%=number+1%> " > 下一页 </ a >      <!--  提供下一页超链接  -->
         </ logic:greaterThan >              
     </ td >
       </ tr >
    </ table >   </ form ></ td >
     </ tr >
</ table >
</ body >
</ html >

             (5)、Struts-config.xml

 

 1 <? xml version = " 1.0 "  encoding = " UTF-8 " ?>
 2 <! DOCTYPE struts - config PUBLIC  " -//Apache Software Foundation//DTD Struts Configuration 1.2//EN "  
 3
 4 " http://struts.apache.org/dtds/struts-config_1_2.dtd " >
 5
 6 < struts - config >
 7    < data - sources  />
 8 < form - beans >
 9       < form - bean name = " peopleForm "  type = " com.domain.PeopleForm "   />       
10 </ form - beans >
11    < global - exceptions  />
12    < global - forwards  />
13 < action - mappings  >
14      < action name = " peopleForm "  path = " /peopleAction "  scope = " request "
15    type = " com.action.PeopleAction "  validate = " true " >
16      < forward name = " peopleAction "  path = " /pagination.jsp "   />
17    </ action >       
18 </ action - mappings >
19    < message - resources parameter = " com.yourcompany.struts.ApplicationResources "   />
20 </ struts - config >
21