Nullpointer with RowSet

[Lucas Moraes]

Hi everybody, I'm currently studying for the OCPJP 7 and I'm programming some JDBC classes, It was all ok until I found this strange bug and want to know why is this happening.

The situation is as follows:

I have this class TestRowSet.java:

package com.lucas.jdbc;

import java.sql.*;
import javax.sql.*;
import javax.sql.rowset.*;
public class TestRowSet{


public static void main(String...args){


  try(JdbcRowSet row = RowSetProvider.newFactory().createJdbcRowSet();){


    row.setUrl("jdbc:mysql://localhost:3306/school");
    row.setUsername("root");
    row.setPassword("*****");

    row.setAutoCommit(false);
    row.setCommand("select * from Student ");
    row.execute();
    row.moveToInsertRow();
    row.updateString("student_name",args[0]);
    row.updateInt("score",Integer.parseInt(args[1]));
    row.insertRow();
    row.moveToInsertRow();
    row.updateString("student_name","JDBC RowSet");
    row.updateInt("score",100);
    row.insertRow();
    row.commit();

    row.first();  //NullPointer
    while(row.next()){

      System.out.println("Student: "+row.getString("student_name")+" || Score: "+row.getInt("score"));

   }





  }catch(Exception e){e.printStackTrace();}



}

}

but I'm getting a nullpointer when the code reaches row.first() method, and if I remove this line the nullpointer is at row.next() instead, as if there is no resultset object anymore after the commit method.

if I remove the row.commit method, the code prints fine(only doesn't save anything on the database) , and strangest yet is that I have a similar class using the plain old ResultSet instead:

package com.lucas.jdbc;
import java.sql.*;
import javax.sql.*;

public class InsertData{


 

public static void main(String...args){
  ResultSet rs = null;

  try(Connection c = DriverManager.getConnection("jdbc:mysql://localhost:3306/school","root","****");

       Statement stm = c.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,ResultSet.CONCUR_UPDATABLE);
       ){
         c.setAutoCommit(false);
         String name = args[0];
         int score = Integer.parseInt(args[1]);

         rs = stm.executeQuery("select * from student");
         rs.moveToInsertRow();
         rs.updateString("student_name",name);
         rs.updateInt("score",score);
         rs.insertRow();
         rs.moveToInsertRow();
         rs.updateString("student_name","Java");
         rs.updateInt("score",95);
         rs.insertRow();
         c.commit();
        while(rs.next()){
          System.out.println("Student: "+rs.getString("student_name")+" | "+rs.getInt("score"));



        }





  }catch(Exception e){

     e.printStackTrace();

  }finally{
    try{
      rs.close();
    }catch(Exception e){e.printStackTrace();}
  }

}


}

But this class runs fine, so I'm wondering, what is wrong in the rowset class? is there any difference between Connection.commit() and JdbcRowSet.commit()?

[Lucas Moraes]

Is the question really that difficult? or I didn't explained clear enough?

[Jeanne Boyarsky]

Your explanation is fine. It seems like a bug in the driver, not something we can explain.