JSP对SQL SERVER进行数据库操作的奇怪问题～～～～
package test;
import test.*;
import java.sql.*;
public class Typebean
{
String typeid= " ";
String typename= " ";
Connection conn=null;
ResultSet rs=null;
Statement sta=null;
public Typebean()
{
String user= "sa ";
String pass= "8760747 ";
String driverName = "com.microsoft.sqlserver.jdbc.SQLServerDriver ";
String dbURL = "jdbc:sqlserver://localhost:1433;DatabaseName=BookStore ";
try{
Class.forName( "com.microsoft.sqlserver.jdbc.SQLServerDriver ");
conn = DriverManager.getConnection(dbURL,user,pass);
sta=conn.createStatement();
}
catch (Exception e)
{
e.printStackTrace();
}
}
public ResultSet getTypeinfo()
{
try
{
sta=conn.createStatement();
rs=sta.executeQuery( "select typename from type ");
}
catch(SQLException e)
{
System.out.println( "捕获了 "+e.getMessage()+ "异常 ");
}
return rs;
}
public void setTypeid(String typeid)
{
this.typeid=typeid;
}
public String getTypeid()
{
return typeid;
}
public void setTypename(String typename)
{
this.typename=typename;
}
public String getTypename()
{
return typename;
}
public boolean executeInsert()
{
boolean b=false;
String sql= "insert into type values( ' "+typename+ " ') ";
try
{
sta.executeUpdate(sql);
b=true;
}
catch(SQLException e)
{
System.out.println( "捕获了 "+e.getMessage()+ "异常 ");
}
return b;
}
public static void main(String args[])
{
Boolean b;
Typebean t=new Typebean();
t.setTypename( "机械书 ");
b=t.executeInsert();
if(b)
System.out.print( "INSERT OK ");
}
}
上面的程序可以得出结果。完全没有问题....
但是如果我把上面的主函数去掉，并且改成javabean.放在JSP里面运行
就提示NULLPOINTEXCEPTIONG
为什么？？？？
%@ page contentType= "text/html; charset=gb2312 " language= "java " import= "java.sql.* " errorPage= " " %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN " "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd ">
<html xmlns= "http://www.w3.org/1999/xhtml ">
<head>
<meta http-equiv= "Content-Type " content= "text/html; charset=gb2312 " />
<title> 无标题文档 </title>
</head>
<jsp:useBean id= "type " class= "test.Typebean " scope= "session "/>
<body>
<!-- <jsp:setProperty name= "type " property= "typename " param= "typename "> </jsp:setProperty> -->
<%
//request.setCharacterEncoding( "GB2312 ");
boolean b=false;
type.setTypename( "机械 ");
b=type.executeInsert();
if(b)
out.print( "添加成功 ");
else
out.print( "添加失败 ");
%>
</body>
</html>
期待高手解答！！！
[解决办法]
出错行是
sta.executeUpdate(sql);
提示
Nullpointerexception~~~
从这里可以看出应该是typename这个参数没有传进去`~
你把String sql= "insert into type values( ' "+typename+ " ') ";改为一个具体的值看看
String sql= "insert into type values( '机械 ') ";如果没有什么问题的话~~
那就是其它问题`~~比如编码，class文件有没有放对什么的``
[解决办法]
<jsp:useBean id= "type " class= "test.Typebean " scope= "session "/>
换成
<%
test.Typebean type=new test.Typebean();
%>