错误信息：
org.apache.jasper.JasperException: An exception occurred processing JSP page /adduser.jsp at line 18
15: %>
16:
17: <%
18: String username = new String(request.getParameter("username").getBytes("ISO-8859-1"));
19: String password = new String(request.getParameter("password").getBytes("ISO-8859-1"));
20: String profession = new String(request.getParameter("profession").getBytes("ISO-8859-1"));
21: String email = new String(request.getParameter("email").getBytes("ISO-8859-1"));
Stacktrace:
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:524)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:435)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
root cause
java.lang.NullPointerException
org.apache.jsp.adduser_jsp._jspService(adduser_jsp.java:75)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:393)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
源码：
<%@page contentType="text/html;charset=gb2312"%>
<%@page import="java.sql.*"%>
<%!
public static final String DBDRIVER = "com.microsoft.sqlserver.jdbc.SQLServerDriver";
public static final String DBURL = "jdbc:sqlserver://localhost:1433; DatabaseName = e_onlineroom";
public static final String DBUSER = "sa" ;
public static final String DBPASS = "sa" ;
%>
<%
Connection conn=null;//定义数据库连接对象
Statement stmt=null;//定义结果集对象
ResultSet rs=null ;//定义SQL对象结果集
%>
<%
String username = new String(request.getParameter("username").getBytes("ISO-8859-1"));
String password = new String(request.getParameter("password").getBytes("ISO-8859-1"));
String profession = new String(request.getParameter("profession").getBytes("ISO-8859-1"));
String email = new String(request.getParameter("email").getBytes("ISO-8859-1"));
%>
<%
//try
//{
Class.forName(DBDRIVER) ;
conn = DriverManager.getConnection(DBURL,DBUSER,DBPASS) ;//建立与数据库的连接
stmt=conn.createStatement();
String sql="select * from huiyuan where username='"+username+"'";
rs=stmt.executeQuery(sql);
if(rs.next()){
%>
<script language="javascript">
alert("此用户名已经存在，请重新注册！")
history.back;
</script>
<%
}else{
String str = "INSERT INTO huiyuan VALUES('"+username+"','"+password+"','"+profession+"','"+email+"')";
stmt.executeUpdate(str);
%>
<script language="javascript">
alert("注册成功！")
window.location.herf=("../login.jsp");
</script>
<%
}
rs.close();
stmt.close();