nested ResultSets

hi every body

i am using nested servlet and it is giving me this error. when i am using single instances of ResultSet and Statement

java.sql.SQLException: Operation not allowed after ResultSet closed

when i am using different instances of ResultSet and Statement

it gives me java.lang.NullPointerException

my code is

private ArrayList searchObjectOnPriv(String priv) throws SQLException,IOException
    {
        
        ArrayList arrlistofobj=new ArrayList();
        Statement st=null;        
        Connection connection=null;
        ResultSet rs=null;
        String query=null;
        try
        {
            Class.forName("com.mysql.jdbc.Driver");
            System.out.println("Found Hardware");
            connection=DriverManager.getConnection("jdbc:mysql://localhost:3306/presize","root","root");
            System.out.println("Connection created");
            st=connection.createStatement();
            query="select EMP_ID,START_DATE,END_DATE from PRIVILEGE where PRIVILEGES='"+priv+"' ";
            rs=st.executeQuery(query);
            while(rs.next())
            {
                //EmpJavaBean emp=new EmpJavaBean();
                //emp.setEmpNumber(rs.getInt("EMP_ID"));
                System.out.println("Inside ist while");
                int empno=rs.getInt("EMP_ID");
                //emp.setEmpFirstName(rs.getString("FIRST_NAME"));
                //emp.setEmpLastName(rs.getString("LAST_NAME"));
                System.out.println("before querry");
                query="select EMP_ID,FIRST_NAME,LAST_NAME,USER_STATUS from USER where EMP_ID= '"+empno+"'";
                System.out.println("after query");
                rs=st.executeQuery(query);
                System.out.println("before 2nd while");
                while(rs.next())
                {
                    System.out.println("Inside 2nd while");                         // here we assume that there are more than one row to rs 
                    EmpJavaBean emp=new EmpJavaBean();                     // after query. and the information of each row is set in 
                    emp.setEmpNumber(rs.getInt("EMP_ID"));                    // javabean object. and finallly the object is added to 
                    emp.setEmpFirstName(rs.getString("FIRST_NAME"));     // ArrayList  arrlistofobj.
                    emp.setEmpLastName(rs.getString("LAST_NAME"));
                    emp.setUserStatus(rs.getInt("USER_STATUS"));

arrlistofobj.add(emp);
                }

}
            
        }catch(Exception e)
        {
            System.out.println("Error is" + e);
        }
        System.out.println("hi");
        return arrlistofobj;

}

here only one object of javabean is able to set into ArrayList and no others

and it gives error: java.sql.SQLException: Operation not allowed after ResultSet closed

in second case

i am using different instances of resultSet and Statement

and no object is set in ArrayList and it gives error : java.lang.NullPointerException

code is

private ArrayList searchObjectOnPriv(String priv) throws SQLException,IOException
    {
        
        ArrayList arrlistofobj=new ArrayList();
        Statement st=null;
        Statement st1=null;
        Connection connection=null;
        ResultSet rs=null;
        ResultSet rs1=null;
        String query=null;
        try
        {
            Class.forName("com.mysql.jdbc.Driver");
            System.out.println("Found Hardware");
            connection=DriverManager.getConnection("jdbc:mysql://localhost:3306/presize","root","root");
            System.out.println("Connection created");
            st=connection.createStatement();
            query="select EMP_ID,START_DATE,END_DATE from PRIVILEGE where PRIVILEGES='"+priv+"' ";
            rs=st.executeQuery(query);
            while(rs.next())
            {
                //EmpJavaBean emp=new EmpJavaBean();
                //emp.setEmpNumber(rs.getInt("EMP_ID"));
                System.out.println("Inside ist while");
                int empno=rs.getInt("EMP_ID");
                //emp.setEmpFirstName(rs.getString("FIRST_NAME"));
                //emp.setEmpLastName(rs.getString("LAST_NAME"));
                System.out.println("before querry");
                query="select EMP_ID,FIRST_NAME,LAST_NAME,USER_STATUS from USER where EMP_ID= '"+empno+"'";
                System.out.println("after query");
                rs1=st1.executeQuery(query);
                System.out.println("before 2nd while");
                while(rs1.next())
                {
                    System.out.println("Inside 2nd while");
                    EmpJavaBean emp=new EmpJavaBean();
                    emp.setEmpNumber(rs1.getInt("EMP_ID"));
                    emp.setEmpFirstName(rs1.getString("FIRST_NAME"));
                    emp.setEmpLastName(rs1.getString("LAST_NAME"));
                    emp.setUserStatus(rs1.getInt("USER_STATUS"));
                    arrlistofobj.add(emp);
                }

}
            
        }catch(Exception e)
        {
            System.out.println("Error is" + e);
        }
        System.out.println("hi");
        return arrlistofobj;

}

can any one please suggest me the solution.

Thanks and regards.

Nothing to do with Servlets; moved to JDBC.

In your first example while you are iterating through your results set you reassing the variable rs to another results set. That is never going to work.

What line does the NullPointerException occur on?

hi

true ..in first case the resultSet rs is being reassigned.
but ,then second case should work.
In second case it is giving nullPointer exception.

In second case it is giving nullPointer exception

it will throw definitely. where is st1 initialized ?

it is initiallised at the start of this function.

it is initiallised at the start of this function.

where is the relevant code for that ? Check again , its not initialized. only st is initialized , not st1.