访问数据库，返回rs后却报nullpointerException,请高手指点

Question

if(username!=null)可能这个一直为空

Answer 1

空口说白话,把NullPointerException的信息贴出来啊

Answer 2

又是这位英雄啊～！来了来了
description The server encountered an internal error () that prevented it from fulfilling this request.exception javax.servlet.ServletException
org.apache.struts.action.RequestProcessor.processException(RequestProcessor.java:545)
org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:486)
org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:274)
org.apache.struts.action.ActionServlet.process(ActionServlet.java:1482)
org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:525)
javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
root cause java.lang.NullPointerException
com.presentation.action.SignonAction.execute(SignonAction.java:55)
org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:484)
org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:274)
org.apache.struts.action.ActionServlet.process(ActionServlet.java:1482)
org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:525)
javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
note The full stack trace of the root cause is available in the Apache Tomcat/5.5.17 logs.

Answer 3

用预备语句试下  把username 换成？
然后用setString(1,username);

Answer 4

对了，我想补充一下
sql="select * from signon where username='"+username+"'";
我把username直接换成
sql="select * from signon where username='abc'";
也还是有这个问题啊～

Answer 5

Sql_data sqldata=new Sql_data();
这句是不是用来建立连接的？连接正常吗？

Answer 6

恩，这个是我的一个数据库bean,那再麻烦大家看下这个bean
 public ResultSet executeQuery(String sql)
   {
try{
     conn=DriverManager.getConnection(url, user, password);
        stmt=conn.createStatementResultSet.TYPE_SCROLL_SENSITIVE,
ResultSet.CONCUR_READ_ONLY);
stmt.executeQuery(sql);
   
   }
   catch(SQLException ex){
System.err.println("Sql_data.executeQuery:"+ex.getMessage());

}   
   return rs;
   }

Answer 7

果然是sqldata问题，li_d_s，太感谢你了！