JSP页中代码：
<%@ page contentType="text/html; charset=gb2312" language="java" import="java.sql.*" errorPage="" %>
<%@ page import="java.lang.*"%>
<jsp:useBean id="connDB" scope="page" class="beans.connDB"/>
<!--<jsp:include page="safe.jsp"/>-->
<%
String id=request.getParameter("id");
String name=request.getParameter("name");
String type=request.getParameter("type");
String date=request.getParameter("date");
String photo=request.getParameter("file");
String price=request.getParameter("price");
String commend=request.getParameter("commend");
String isnew=request.getParameter("isnew");
String introduce=request.getParameter("introduce");
if(introduce.equals("")) introduce="暂无简介！";

ResultSet rs=connDB.executeQuery("select * from jz_product where jz_id='"+id+"'");

if(rs.next())
{
out.print("<script language='javascript'>alert('该编号信息已经存在!');history.back(-1);</script>");
}
else{
introduce=connDB.toStr(introduce);
String sql="insert into jz_product(jz_id,jz_name,jz_type,jz_date,jz_photo,jz_price,jz_commend,jz_isnew,jz_introduce) values('"+id+"','"+name+"','"+type+"','"+date+"','"+photo+"','"+price+"','"+commend+"','"+isnew+"','"+introduce+"')";
int flag=0;
flag=connDB.executeUpdate(sql);
if(flag!=0)
{
out.println("<script language='javascript'>alert('添加成功！');window.location.href='jz_add.jsp';</script>");
}
else
{
out.println("<script language='javascript'>alert('对不起，添加失败！');history.back(-1);</script>");
}
}
%>
ResultSet rs=connDB.executeQuery("select * from jz_product where jz_id='"+id+"'");
//这句话的操作数据库好像根本就没有执行，但是如果我把 上面的connDB.executeQuery改为connDB.executeQuery1也会报错说没有executeQuery1这样的方法.
我在bean中也写了测试语句，测试都是对的，在这里却不行

报错：

java.lang.NullPointerException
    org.apache.jsp.system.jz_005fadd_005fact_jsp._jspService(jz_005fadd_005fact_jsp.java:68)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:97)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:334)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:314)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:264)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:802)

下面是Bean里的代码：就只贴executeQuery（）出来了
public ResultSet executeQuery(String sql){
try{
conn=DriverManager.getConnection("jdbc:microsoft:sqlserver://localhost:1433;DatabaseName=ypx","sa","");
System.out.println("连接成功");
stmt=conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,ResultSet.CONCUR_READ_ONLY);
rs=stmt.executeQuery(sql);
}catch(SQLException e){
System.err.println(e.getMessage());
}
return rs;
}

这应该是没错了，我用main（）测试过是可以的

String id=request.getParameter("id");
String name=request.getParameter("name");
String type=request.getParameter("type");
String date=request.getParameter("date");
String photo=request.getParameter("file");
String price=request.getParameter("price");
String commend=request.getParameter("commend");
String isnew=request.getParameter("isnew");
String introduce=request.getParameter("introduce");

这么大一段你能保证你下面insert的时候所用到的必填字段不为空吗？你一个一个测一下有否有值

在页面中测试输出，bean中可以得到不一定页面中就可以得到！

我把form重新建一下，问题已经解决了，奇怪的很。。。。。谢谢大ga!!!

看了这些
我就知道Hibernate的好处了

有了Hibernate就不用这么麻烦了