用equals函数比较两字符串是否一样出现错误，望大神帮解决
错误提示
type Exception report
message
description The server encountered an internal error () that prevented it from fulfilling this request.
exception
java.lang.NullPointerException
Email.check.doPost(check.java:84)
javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
note The full stack trace of the root cause is available in the Apache Tomcat/6.0.35 logs.
代码出错位置：
if(rs.next())
{
String str=rs.getString("password");
if(userpassword.trim().equals(str.trim())) (第84行，试过if(userpassword.equals(str)))
{
String script = "<script>location.href=\"" + req.getContextPath() + "/test.jsp\"</script>";
resp.getWriter().println(script);
}
}
[解决办法]
