求教。。 为什么加载到servlet页面显示空白或者一直加载页面没显示也没错误？

package com.bean;

public class Example7_2_Bean {
    String[] columnName;// 存放列名
    String[][] tableRecord = null;// 存放查询到的记录
    int pageSize = 1;
    int totalPages = 1;
    int currentPage = 1;
public Example7_2_Bean(){
    
}
    public int getPageSize() {
        return pageSize;
    }

    public void setPageSize(int pageSize) {
        this.pageSize = pageSize;
    }

    public int getTotalPages() {
        return totalPages;
    }

    public void setTotalPages(int totalPages) {
        this.totalPages = totalPages;
    }

    public int getCurrentPage() {
        return currentPage;
    }

    public void setCurrentPage(int currentPage) {
        this.currentPage = currentPage;
    }

    public String[] getColumnName() {
        return columnName;
    }

    public void setColumnName(String[] columnName) {
        this.columnName = columnName;
    }

    public String[][] getTableRecord() {
        return tableRecord;
    }

    public void setTableRecord(String[][] tableRecord) {
        this.tableRecord = tableRecord;
    }

}

package com.servlet;

import com.bean.Example7_2_Bean;

import java.sql.*;
import java.io.*;

import javax.servlet.*;
import javax.servlet.http.*;

public class Example7_2_Servlet extends HttpServlet {
    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    Connection con;
    Statement sql;
    ResultSet rs = null;

    @Override
    public void init(ServletConfig config) throws ServletException {
        // TODO Auto-generated method stub
        super.init(config);
    }

    public String handleString(String s) {
        try {
            byte b[] = s.getBytes("iso-8859-1");
            s = new String(b);
        } catch (Exception ee) {
        }
        return s;
    }

    @Override
    public void doPost(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        // TODO Auto-generated method stub

        Example7_2_Bean resultBean = null;// 放在外面是为了判断这个是否为空，
        try {
            resultBean = (Example7_2_Bean) req.getAttribute("resultBean");
            // 获取的是bean的对象
            if (resultBean == null) {// 对获取到的javabean对象进行判断
                resultBean = new Example7_2_Bean();// 若为空则创建javabean对象
                req.setAttribute("resultBean", resultBean);//
            }

        } catch (Exception e) {
            // TODO: handle exception
            resultBean = new Example7_2_Bean();// 若为空则创建javabean对象
            req.setAttribute("resultBean", resultBean);//
        }

        try {
            Class.forName("com.mysql.jdbc.Driver");
        } catch (Exception e) {
        }
        String dataBase = req.getParameter("dataBase");
        String tableName = req.getParameter("tableName");
        String nu = req.getParameter("number");
        String na = req.getParameter("name");
        String mT = req.getParameter("madeTime");
        String pr = req.getParameter("price");
        // trim函数用于删除文本的空格

        Float p = Float.parseFloat(pr);
        String condition = "insert into" + tableName + "values" + "(" + "'"
                + nu + "','" + na + "','" + mT + "'," + p + ")";
        boolean boo = (nu.length() > 0);
        try {
            String uri = "jdbc:mysql://127.0.0.1/warehouse?"
                    + "user=root&password=123456&characterEncoding=gb2312";

            con = DriverManager.getConnection(uri);
            sql = con.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,
                    ResultSet.CONCUR_READ_ONLY);
            if (boo)
                sql.executeUpdate(condition);
            boolean m = rs.next();
            if (m == true) {
                // 调用登入成功的方法:
                success(req, resp);

            } else {
                String backNews = "你输入的用户名不存在或密码不匹配";
                // 调用失败的方法
                fail(req, resp, backNews);
            }

            con.close();

            // boolean m = rs.next();
            // if (m == true) {
            // // 调用登入成功的方法:
            // success(req, resp, logname, password);
            //
            // RequestDispatcher dispatcher = req
            // .getRequestDispatcher("shanping/showRecord.jsp");
            // dispatcher.forward(req, resp);
            //
            // } else {
            // String backNews = "你输入的用户名不存在或密码不匹配";
            // // 调用失败的方法
            // fail(req, resp, logname, backNews);
            // }

        } catch (SQLException e) {
            System.out.println(e);
            fail(req, resp, "添加记录失败" + e.toString());
        }

    }

    public void success(HttpServletRequest req, HttpServletResponse resp)
            throws SQLException, ServletException, IOException {
        // TODO Auto-generated method stub
        Example7_2_Bean resultBean = null;// 放在外面是为了判断这个是否为空，
        try {
            resultBean = (Example7_2_Bean) req.getAttribute("resultBean");
            // 获取的是bean的对象
            if (resultBean == null) {// 对获取到的javabean对象进行判断
                resultBean = new Example7_2_Bean();// 若为空则创建javabean对象
                req.setAttribute("resultBean", resultBean);//
            }

        } catch (Exception e) {
            // TODO: handle exception
            resultBean = new Example7_2_Bean();// 若为空则创建javabean对象
            req.setAttribute("resultBean", resultBean);//
        }
        rs = sql.executeQuery("select * from product");
        ResultSetMetaData metaData = rs.getMetaData();
        int columnCount = metaData.getColumnCount();// 得到结果集的列数
        String[] columnName = new String[columnCount];
        for (int i = 0; i < columnName.length; i++) {
            columnName[i] = metaData.getColumnName(i + 1);// 获得列名
        }
        resultBean.setColumnName(columnName);// 更新javabean数据模型
        rs.last();// 为BoolEAN类型
        int rowNumber = rs.getRow();// 得到记录数
        String[][] tableRecord = resultBean.getTableRecord();
        tableRecord = new String[rowNumber][columnCount];
        rs.beforeFirst();
        int i = 0;
        while (rs.next()) {
            for (int k = 0; k < columnCount; k++) {
                tableRecord[i][k] = rs.getString(k + 1);
                i++;
            }
            resultBean.setTableRecord(tableRecord);// 更新javabean数据模型
            con.close();
            RequestDispatcher dispatcher = req
                    .getRequestDispatcher("shanping/showRecord.jsp");
            dispatcher.forward(req, resp);
        }
    }

    // public void success(HttpServletRequest req, HttpServletResponse resp,
    // String logname, String password) {
    // // TODO Auto-generated method stub
    //
    // Example7_2_Bean resultBean = null;// 放在外面是为了判断这个是否为空，
    // try {
    // resultBean = (Example7_2_Bean) req.getAttribute("resultBean");//
    // 获取的是bean的对象
    // if (resultBean == null) {// 对获取到的javabean对象进行判断
    // resultBean = new Example7_2_Bean();// 若为空则创建javabean对象
    // req.setAttribute("resultBean", resultBean);//
    // }
    //
    // } catch (Exception e) {
    // // TODO: handle exception
    // resultBean = new Example7_2_Bean();// 若为空则创建javabean对象
    // req.setAttribute("resultBean", resultBean);//
    // }
    //
    //
    // }
    // }

    public void fail(HttpServletRequest req, HttpServletResponse resp,
            String backNews) {
        // TODO Auto-generated method stub
        resp.setContentType("text/html;charset=gb2312");
        try {
            PrintWriter out = resp.getWriter();
            out.print("<html><body>");
            out.print("<h2>" + backNews + "<h2>");
            out.print("<a href='example7_2.jsp'>输入正确信息");
            out.print("</html></body>");
        } catch (IOException exp) {
        }
    }

    @Override
    public void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        // TODO Auto-generated method stub
        doPost(req, resp);
    }

}

<%@ page language="java" import="java.util.*" pageEncoding="gb2312"%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>My JSP 'example7_2.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">
<!--
    <link rel="stylesheet" type="text/css" href="styles.css">
    -->

</head>

<body>
    查询warehouse数据库product表中
    <form action="<%=request.getContextPath()%>/Example7_2_Servlet" method="post">
        <br>产品号<input type="text" name="number" >
        <br>名称:<input type="text" name="name" >
        <br>生产日期:<input type="text" name="madeTime" >
        <br>价格:<input type="text" name="price" >
         <input
            type="submit" name="g" value="提交">
    </form>


</body>
</html>

<%@ page language="java" import="java.util.*" pageEncoding="gb2312"%>
<jsp:useBean id="resultBean" class="com.bean.Example7_2_Bean"
    scope="request"></jsp:useBean>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>My JSP 'showRecord.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">
<!--
    <link rel="stylesheet" type="text/css" href="styles.css">
    -->

</head>

<body>
    <br>当前显示的内容是:
    <jsp:setProperty property="pageSize" name="resultBean" param="pageSize"/>
    <jsp:setProperty property="currentPage" name="resultBean" param="currentPage"/>
    <table border="1">
        <%
            String[] columnName = resultBean.getColumnName();
                if(columnName!=null){
                out.print("<tr>");
                for(int i=0;i<columnName.length;i++){
                out.print("<th>"+columnName[i]+"</th>");
                }
                out.print("<tr>");
                }
            
            
            String[][] record = resultBean.getTableRecord();
                if(record==null){
                out.print("没有记录");
                return;
                }
            
            
                int totalRecord = record.length;
                    out.println("全部记录数" + totalRecord);//全部记录数
                    int pageSize = resultBean.getPageSize();//每页显示的记录数
                    int totalPages = resultBean.getTotalPages();
                    if (totalRecord % pageSize == 0)
                        totalPages = totalRecord / pageSize;//总页数
                    else
                        totalPages = totalRecord / pageSize + 1;
                    resultBean.setPageSize(pageSize);
                    resultBean.setTotalPages(totalPages);
                    if (totalPages >= 1) {
                        if (resultBean.getCurrentPage() < 1)
                            resultBean.setCurrentPage(resultBean.getTotalPages());
                        if (resultBean.getCurrentPage() > resultBean.getTotalPages())
                            resultBean.setCurrentPage(1);
                        int index = (resultBean.getCurrentPage() - 1) * pageSize;
                        int start=index;//查询位置移动到currentPage页起始位置
                        
                        for (int i = index; i < pageSize+index; i++) {
                            if(i==totalRecord)
                            break;
                            out.print("<tr>");
                            for(int j=0;j<columnName.length;j++){
                            out.print("<td>"+record[i][j]+"</td>");}

                        }
                        out.print("</tr>");
                    }
            %>
            </table>
            <br>每页最多显示<jsp:getProperty property="pageSize" name="resultBean" />条信息
            <br>当前显示第
            <font color=blue> <jsp:getProperty property="currentPage"
            name="resultBean" /> 页，共有<jsp:getProperty property="totalPages"
            name="resultBean" /></font>页。
            <table>
                <tr>
            <td>
            
            <form action="" method="post">
                <input type="hidden" name="currentPage" value="<%=resultBean.getCurrentPage() - 1
        %>">
        <input type="submit" name="g" value="上一页">
        </form>
        </td>
        <td><form action="" method="post">
                <input type="hidden" name="currentPage"
                    value="<%=resultBean.getCurrentPage() + 1%>"> <input
                    type="submit" name="g" value="下一页">
            </form></td>
        </tr>

        <tr>
            <td><form action="" method="post">
                    每页显示<input type="text" name="PageSize" value=1 size=3> 条记录<input
                        type="submit" name="g" value="确定">
                </form></td>

            <td><form action="" method="post">
                    输入页码<input type="text" name="currentPage" size=2> <input
                        type="submit" name="g" value="提交">
                </form></td>
        </tr>

    </table>


</body>
</html>

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://java.sun.com/xml/ns/javaee"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
    id="WebApp_ID" version="3.0">

    <servlet>
        <servlet-name>Example7_2_Servlet</servlet-name>
        <servlet-class>com.servlet.Example7_2_Servlet</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>Example7_2_Servlet</servlet-name>
        <url-pattern>/Example7_2_Servlet</url-pattern>
    </servlet-mapping>
</web-app>

经过长时间的检查。发现最终还是代码有问题，一定要仔细代码， 从最基础， 最没有可能错误的地方开始查找错误。