Question

Can someone help me with this: I’m making a java database application and I want to put my methods for select,insert,update and delete into separated class so they can be called from another classes and reused.
Till now I managed to separate only methods for update and delete and for insert when not using prepared statement. Problem I’m encountering is how to return data’s when doing select from database and put them into table.

Here are my update and delete method’s in Queries class:

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import com.Konekcija.Konekcija;

public class Queries {
Konekcija konekcija = new Konekcija();

public void updateTable(String sqlQuery){
    Connection conn = null;
    Statement st = null;
    try{
        Class.forName("com.mysql.jdbc.Driver");
        conn = konekcija.getConn();
        st = conn.createStatement();
        st.executeUpdate(sqlQuery);

    }catch(Exception e){
        e.printStackTrace();
    }finally{
        try {
            conn.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        try {
            st.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

public void deleteFromTable(String sqlQuery){
    Connection conn = null;
    Statement st = null;
    try{
        Class.forName("com.mysql.jdbc.Driver");
        conn = konekcija.getConn();
        st = conn.createStatement();
        st.executeUpdate(sqlQuery);
    }catch(Exception e){
        e.printStackTrace();
    }finally{
        try {
            conn.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        try {
            st.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

}

P.S. Connection properties are in another class “Konekcija”

Answer 1

You should create a collection and populate it with the results of the query, it should look something like:

List<Foo> selectFoos(Connection connection) throws SQLException {
    PreparedStatement ps = connection.prepareStatement("select * from foo");
    try {
        ResultSet resultSet = ps.executeQuery();
        try {
            List<Foo> foos = new ArrayList<Foo>();
            while (resultSet.next()) {
                Foo foo = new Foo();
                // use resultSet methods get... to retrieve data from current row of results
                // and populate foo
                foos.add(foo);
            }
        } finally {
            resultSet.close();
        }
    } finally {
        ps.close();
    }
    return foos;
}