java.lang.NullPointerException

dbcon bean：
package dc;
import java.sql.*;
import javax.servlet.http.*;
import java.io.*;

public class dbcon implements HttpSessionBindingListener{
private Connection con=null;
public dbcon(){
BuildConnection();
}
private void BuildConnection(){
try{
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
con=DriverManager.getConnection("jdbc:odbc:test");
}
catch(Exception ex){
System.out.print(ex.toString());
}
}

public Connection getConnection(){
if(con==null)
BuildConnection();
return this.con;
}

public void close()
{
try{
con.close();
con=null;
}
catch(SQLException sex){
System.out.println(sex.toString());
}
}

public void valueBound(HttpSessionBindingEvent event){}
public void valueUnbound(HttpSessionBindingEvent event){
if(con!=null)
close();
}
}

votebean:

package dc;
import java.sql.*;

public class VoteBean{
private Connection con=null;
private Statement stmt=null;
private ResultSet BookRs=null;

public  VoteBean(){
}

public void InitBookRs(Connection con)
{
try{
this.con=con;
stmt=this.con.createStatement(
ResultSet.TYPE_SCROLL_SENSITIVE,
ResultSet.CONCUR_READ_ONLY);
BookRs=stmt.executeQuery("select * from uin");
}
catch(SQLException sex){
System.out.println(sex.toString());
}
}

public void CloseBookRs(){
try{
if(BookRs!=null){
BookRs.close();
BookRs=null;
}
if(stmt!=null){
stmt.close();
stmt=null;
}
}
catch(SQLException sex){
System.out.println(sex.toString());
}
}

public boolean next(){
boolean result=false;
try{
result=BookRs.next();
}
catch(SQLException sex){
System.out.println(sex.toString());
}
return result;
}

public boolean login(Connection con,String un,String pw){
boolean result=false;
String sql="select * from uin where un='"+un+"' and pw='"+pw+"'";

try{
this.con=con;
Statement lstmt=null;
lstmt=this.con.createStatement(
ResultSet.TYPE_SCROLL_INSENSITIVE,
ResultSet.CONCUR_READ_ONLY);

ResultSet rs=lstmt.executeQuery(sql);
result=rs.next();
rs.close();
}
catch(SQLException sex){
System.out.println(sex.toString());
}
return result;
}

}

jsp调用：




excute

一,测试数据库是否连接成功;
二,测试rs是否为null

可以用System.out.println 大法，定位在那里出的异常···就好解决了