How do I create a Java object from the resultset of a select query?

Question

Connection to JDBC is working fine. This is the code which accesses database tables. File name –

FlightDB.java Schema – Flights1(flno int, time timestamp)

public static Flight selectFlight(Flight flight) throws SQLException{
    PreparedStatement ps = null;
    ResultSet rs = null;
    String q1 = "Select * from Flights1 f order by f.time";
    Flight flight1 = null;
    try{
        ps = connection.prepareStatement(q1);
        rs = ps.executeQuery();
        while(rs.next()){
            Flight flight1 = new Flight();
            flight1 = new Flight();
            flight1.setflno(rs.getInt(1));
            flight1.settime(rs.getTimestamp(2));
            // System.out.println(“new flight:” +flight1.getflno()); Correct output printed here
        }
    }
    finally{
        closeResultSet(rs);
        closePreparedStatement(ps);
    }
    return flight;
}

And this is a part of top-level code------------ File name : Display.java

static Flight showFlights(ResultSet rs) throws SQLException {
    Flight flight1 = new Flight();
    AirDB.selectFlight(flight1);
    // flight1.setflno(rs.getInt(1));
    // flight1.settime(rs.getTimestamp(2));
    System.out.println("New flight " + flight1.getflno());//OP: New flight 0
    return flight1;
}

And this is my class Flight ---- Flight.java

public Flight() {
    flno = 0;
    time = null;
}

public Flight(int flno ,Timestamp time)
{
    this.flno = flno;
    this.time = time;
}

public int getflno(){
    return flno;
}

public void setflno(int flno){
    this.flno = flno;
}

public Timestamp gettime(){
    return time;
}

public void settime(Timestamp time){
    this.time = time;
}

I get 0(default value) as my output which is not correct. I want to print the output from the top-level java file. I tried using flight1 = AssignFlights1.showFlights(rs); in FlightDB.java too.

Thank you for looking at this code. Can you please help me in this. Thanks you.

Scary Wombat · Accepted Answer · 2016-11-25 06:54:17Z

4

You are returning the wrong Object (also see my inline comments)

try

public static Flight selectFlight() throws SQLException{  // no param needed
  PreparedStatement ps = null;
  ResultSet rs = null;

  // I guess that this will not be the query you want in the end
  String q1 = "Select * from Flights1 f order by f.time";        
  Flight flight1 = null;
  try{
    ps = connection.prepareStatement(q1);
    rs = ps.executeQuery();
    if (rs.next()){  // only returning one object so no needed for while
      flight1 = new Flight();
      flight1.setflno(rs.getInt(1));
      flight1.settime(rs.getTimestamp(2));
      System.out.println(“new flight:” +flight1.getflno()); Correct output printed here
    }
  }
  finally{
    closeResultSet(rs);
    closePreparedStatement(ps);
  }
  return flight1;
}

Also if you correctly indent your code it is alot easier to read and debug

edited Nov 25, 2016 at 6:54

answered Nov 25, 2016 at 6:43

Scary Wombat

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2 Comments

chillie Over a year ago

Thank you for your response. Sorry but I didn't mention, I have to return multiple rows here.

Scary Wombat Over a year ago

In that case add them to (and return an) ArrayList<Flight>

Vasu · Accepted Answer · 2016-11-25 06:44:50Z

You should return flight1 object not flight as shown below:

public static Flight selectFlight() throws SQLException{
    PreparedStatement ps = null;
    ResultSet rs = null;
    String q1 = "Select * from Flights1 f order by f.time";
    Flight flight1 = null;
try{
    ps = connection.prepareStatement(q1);
    rs = ps.executeQuery();
    if(rs.next()){
        flight1 = new Flight();
        flight1.setflno(rs.getInt(1));
        flight1.settime(rs.getTimestamp(2));
        // System.out.println(“new flight:” +flight1.getflno()); Correct output printed here
        }
    }
finally{
    closeResultSet(rs);
    closePreparedStatement(ps);
}
    return flight1;
}

Also, DO NOT use while for single record, rather use if for single record.

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