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MVC模式下用Servlet和jsp分页的HelloWord
MVC模式下分页：
马克-to-win：像淘宝百度这样的类似网页，我们用了很多很多。基本上就是输入查询条件以后，符合查询条件的结果可能会成千上万。我们不能一下子把所有这些结果都列出来，只能一次显示一页。当用户按下一页的时候，才会把下一页的内容列出来。这样不至于内存崩溃。要达到这样的效果，要用到分页技术。分页技术的核心思想就是把所有的结果放在一个ArrayList的当中(在我们的例子当中就是ArrayList ret)。马克-to-win：这个ArrayList连同相关参数比如一共有多少行（totalNumberOfRowsInDB），每页有多少行（pageSize），当前显示是第几页（currentPageNumber），一共有多少页（totalNumberOfPages），都放在Session当中。马克-to -win：返回到jsp后，再从Session当中取出所有这些数据,把它显示出来。注意这里数据库的每行数据都对应一个RegisterRow实例。把所有这些实例都放在ArrayList当中。如果你觉得全部把结果放在Session当中浪费空间的话，你甚至一次只放5页，当用户访问第5页的时候，你就再一次访问数据库，把数据放在Session当中。算法由你自己定义，据情况而定。当然，为简单起见，我们的例子是把所有符合条件的数据都给取出来。
例1.3.1：
home.jsp:
<%@ page contentType="text/html; charset=GBK" %>
<html>
<form method="post" action="MarkToWinServlet">
每页 <input type="text" name="pagesize" value="2">条
第 <input type="text" name="pageno" value="3">页
查id小于 <input type="text" name="id" value="8">
<input type="submit" name="Submit" value="Submit">
</form>
<hr>
既然这是首页，像淘宝首页一样，这底下是首页的一些泛泛信息。
</html>
package com;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class ServletHello1 extends HttpServlet {
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
request.setCharacterEncoding("GBK");
String pageno = request.getParameter("pageno");
String pagesize = request.getParameter("pagesize");
String id = request.getParameter("id");
MyBean mb = new MyBean();
try {
mb.getData(pageno, pagesize, id);
} catch (Exception e) {
e.printStackTrace();
}
request.getSession().setAttribute("myBean", mb);
response.sendRedirect("show.jsp");
}
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doPost(request, response);
}
}
MyBean.java:
package com;
import java.sql.*;
import java.util.ArrayList;
public class MyBean {
/* 下面一大堆变量，jsp中都需要取到，所以是类变量， 非局部 */
private int totalNumberOfRowsInDB; // 数据表中总共存储了多少行
private int pageSize;
private int currentPageNumber;
private int totalNumberOfPages;
private int id;
private ArrayList ret;
public void getData(String curpage, String pagesizeS, String idS)
throws Exception {
Connection con;
/*
* MysqlConnectionPoolDataSource ds is always in the memory once it is
* created becasue it is static..
*/
con = DatabaseConn.getConnection();
if (curpage == null) {
currentPageNumber = 1; // 如果“PAGE”为NULL时将当前页面设置为1
} else {
currentPageNumber = Integer.parseInt(curpage);
if (currentPageNumber < 1) { // 如果当前页小于1，将当前页设置为1
currentPageNumber = 1;
}
}
id = Integer.parseInt(idS);
pageSize = Integer.parseInt(pagesizeS);
int i = 0;
ret = new ArrayList();
Statement stm = null;
ResultSet rs = null;
stm = con.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,
ResultSet.CONCUR_UPDATABLE);
String sql = "select * from register where id<" + id;
rs = stm.executeQuery(sql);
rs.last();
totalNumberOfRowsInDB = rs.getRow();
totalNumberOfPages = (totalNumberOfRowsInDB + pageSize - 1) / pageSize;
if (currentPageNumber > totalNumberOfPages)
currentPageNumber = totalNumberOfPages;
rs.absolute((currentPageNumber - 1) * pageSize + 1);
while (i < pageSize && !rs.isAfterLast()) {
RegisterRow rr = new RegisterRow();
rr.setId(rs.getInt(1));
rr.setName(rs.getString(2));
rr.setAge(rs.getInt(3));
ret.add(rr);
rs.next();
i++;
}
stm.close();
con.close();
}
public int getCurrentPageNumber() {
return currentPageNumber;
}
public void setCurrentPageNumber(int currentPageNumber) {
this.currentPageNumber = currentPageNumber;
}
public int getTotalNumberOfRowsInDB() {
return totalNumberOfRowsInDB;
}
public int getPageSize() {
return pageSize;
}
public int getTotalNumberOfPages() {
return totalNumberOfPages;
}
public int getId() {
return id;
}
public ArrayList getRet() {
return ret;
}
}
show.jsp:
<%@ page contentType="text/html; charset=GBK" import="java.sql.*"%>
<%@ page import="com.*,java.util.*"%>
<html>
<head>
<title>分页</title>
</head>
<body>
<center>
<%
int totalNumberOfRowsInDB = 0;//数据库总共多少条记录the total number of the rows in the DB.
int totalnumberOfPages = 0;//总共多少页the total number of the pages
int currentpagenumber = 0;//当前是第几页currentpagenumber means current page.
int i = 0;
int id = 0;
int pageSize = 0;
MyBean myBean = ((MyBean) session.getAttribute("myBean"));
if (myBean != null) {
currentpagenumber = myBean.getCurrentPageNumber();
id = myBean.getId();
totalnumberOfPages = myBean.getTotalNumberOfPages();//计算出总的页数
pageSize = myBean.getPageSize();
}
%>
<form method="post" action="MarkToWinServlet">
<br> 第<%=currentpagenumber%>页 共<%=totalnumberOfPages%>页
<%
if (currentpagenumber < totalnumberOfPages) {//如果当前页小于总页数
%>
<a
href="MarkToWinServlet?pageno=<%=currentpagenumber + 1%>&pagesize=<%=pageSize%>&id=<%=id%>">下一页< /a>
<%
}
%>
<%
if (currentpagenumber > 1)//如果当前页大于1
{
%>
<a
href="MarkToWinServlet?pageno=<%=currentpagenumber - 1%>&pagesize=<%=pageSize%>&id=<%=id%>">上一页< /a>
<%
}
%>
第<input type="text" name="pageno" value="<%=currentpagenumber%>">页，
id小于<input name="id" value="<%=id%>">，每页共<input name="pagesize"
value="<%=pageSize%>">条 <br> <input type="submit"
name="Submit" value="Submit">
</form>
像淘宝的搜寻一样，结果就显示在下面：
<hr>
<table border="1">
<tr>
<td>ID</td>
<td>名字</td>
<td>年龄</td>
</tr>
<%
if (totalnumberOfPages > 0) {
ArrayList ret = (ArrayList) myBean.getRet();
Iterator it = ret.iterator();
while (it.hasNext()) {
RegisterRow temp = (RegisterRow) it.next();
out.println("<TR>");
out.println("<td>" + temp.getId() + "</td>");
out.println("<td>" + temp.getName() + "</td>");
out.println("<td>" + temp.getAge() + "</td>");
out.println("</tr>");
}
}
%>
</table>
<br>
</center>
</body>
</html>
RegisterRow.java:
package com;
public class RegisterRow {
int id;
String name;
int age;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
}
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