分页代码

 

分页的方式：
    页面分页
    数据库分页（现在通用的分页方式）：一次取数据的一部分，尽量采取数据库
    机制来实现！

 

除了SQL 和 Access外 其他的数据库都提供了数据库分页机制，现在来用通用的分页方法来实现：游标分页！

 

本代码是基于java的反射机制实现！

 

首先：在数据库连接时给定参数，代码：

Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");             conn = DriverManager.getConnection("jdbc:odbc:test");             stmt = conn.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,ResultSet.CONCUR_UPDATABLE);

  建立main方法进行测试：

public static void main(String[] args) throws Exception {         BaseDao db = new BaseDao();         int pageSize = 3;//每页三条         int pageNow = 1;//当前第一页         ResultSet rs = db.executeQuery("select * from message");         rs.absolute((pageNow-1)*pageSize+1);         for (int i = 0; i < pageSize; i++) {             System.out.println(rs.getString(2));             if(!rs.next()) break;                      }     }

   测试成功 OK！ 继续

接着：在数据库操作方法中，写入一下代码：

//分页中获取总列数专用     public int getCount(String sql)     {         int count = 0;         BaseDao db = new BaseDao();         ResultSet rs;         try {             rs = db.executeQuery(sql);             if(rs.next())                 count = rs.getInt(1);         } catch (SQLException e) {             // TODO Auto-generated catch block             e.printStackTrace();         }finally         {             db.close();         }         return count;     }          //分页专用     public List executeQuery(String sql,int pageNow,int pageSize ) {         // TODO Auto-generated method stub         List list = new ArrayList();         BaseDao dao = new BaseDao();         ResultSet rs;         try {             rs=dao.executeQuery(sql);             rs.absolute((pageNow-1)*pageSize+1);             String[] fields=new String[rs.getMetaData().getColumnCount()];             for (int i = 0; i < fields.length; i++) {                 fields[i]=rs.getMetaData().getColumnName(i+1);             }             for(int p=0;p<pageSize;p++)             {                 HashMap mp = new HashMap();                 for (int i = 0; i < fields.length; i++) {                     String value = rs.getString(fields[i]);                     mp.put(fields[i], value);                                      }                 list.add(mp);                 if(!rs.next()) break;             }         } catch (Exception e) {             // TODO: handle exception             e.printStackTrace();         }finally         {             dao.close();         }         return list;     }

其次：封装PageServlet类，用来具体实现分页的代码：

 

public class PageServlet extends HttpServlet {     public void service(HttpServletRequest request, HttpServletResponse response)             throws ServletException, IOException {         int pageNow = 1;         int pageSize = 5;         String temp = request.getParameter("pageNow");         if (temp != null)             pageNow = Integer.parseInt(temp);         Method method;         Object[] objs = null;         try {             method = this.getClass().getDeclaredMethod("page",                     new Class[] { int.class, int.class });             objs = (Object[]) method.invoke(this, new Object[] { pageNow,                     pageSize });         } catch (Exception e) {             // TODO Auto-generated catch block             e.printStackTrace();         }         request.setAttribute("message", objs[0]);         request.setAttribute("pageCount", objs[2] + "");         request.setAttribute("count", objs[1] + "");         request.setAttribute("pageNow", pageNow + "");         request.getRequestDispatcher(objs[3].toString()).forward(request,                 response);     } }

接着：在具体操作方法BoardDao中的代码：

 

//分页中查询共有的列数      public int getCount() {         // TODO Auto-generated method stub          return db.getCount("select count(*) from message");     }           //分页中获取所有页数      public int getPageCount(int pageSize) {         // TODO Auto-generated method stub          return (getCount()+pageSize-1)/pageSize;     }          //执行查询方法     public List findAll(int pageNow,int pageSize)     {                  String sql = "SELECT dbo.message.messageid, dbo.message.title, dbo.message.content, dbo.message.marktime, dbo.userInfo.username FROM dbo.message INNER JOIN dbo.userInfo ON dbo.message.userid = dbo.userInfo.id";         return db.executeQuery(sql,pageNow,pageSize);                  }

最后：在控制器ShowServlet（继承PageServlet ）中进行引用，查询结果集显示在MessageBoard.jsp

 

public class ShowServlet extends PageServlet {     public Object[] page(int pageNow, int pageSize) {         BoardDao dao = new BoardDao();         List list = dao.findAll(pageNow, pageSize);         int count = dao.getCount();         int pageCount = dao.getPageCount(pageSize);         return new Object[] { list, count, pageCount, "MessageBoard.jsp" };     } }

 

在MessageBoard.jsp代码：

<TABLE align="center" border="0" width="30%" > <TR>     <TD><a href="./ShowServlet?pageNow=1">首页</a></TD>     <c:if test="${pageNow<pageCount}">         <TD><a href="./ShowServlet?pageNow=${pageNow+1}">下一页</a></TD>         </c:if>     <c:if test="${pageNow==pageCount}">         <TD>下一页</TD>         </c:if>     <c:if test="${pageNow>1}">         <TD><a href="./ShowServlet?pageNow=${pageNow-1}">上一页</a></TD>     </c:if>     <c:if test="${pageNow==1}">         <TD>上一页</TD>     </c:if>     <TD><a href="./ShowServlet?pageNow=${pageCount}">末页</a></TD>     <TD>${pageNow}/${pageCount} 总共:${count }</TD> </TR> </TABLE>

到此，分页已经完成