Error performing query: javax.servlet.ServletException: org.xml.sax.SAXParseException: Content is not allowed in prolog.

import java.io.*;
import java.util.*;
import java.sql.*;           // JDBC packages
import javax.servlet.*;
import javax.servlet.http.*;
import javax.xml.parsers.*;
import org.xml.sax.*;
import org.xml.sax.helpers.*;

public class step5 extends HttpServlet {

   public static final String DRIVER = "sun.jdbc.odbc.JdbcOdbcDriver";
   public static final String URL = "jdbc:odbc:rreOracle";
   public static final String username = "cm485a10";
   public static final String password = "y4e8f7s5";

   SAXParserFactory factory;

   public void init() throws ServletException {

      factory = SAXParserFactory.newInstance();
   }

   public void doGet (HttpServletRequest  request,
                      HttpServletResponse response)
      throws ServletException, IOException
      {
      PrintWriter out = response.getWriter();
      Connection con = null;

      try {

            Class.forName(DRIVER);

            con = DriverManager.getConnection(URL,username,password);

            try {
               Statement stmt = con.createStatement();
               ResultSet rs = stmt.executeQuery("SELECT sale_id, home_id, agent_id, customer_id FROM sale");

               String xml = "";
               xml = xml + "<sales_description>";
               xml = xml + "<sale>";

               boolean courseDataDone = false;
               while (rs.next()) {
                  String sale_id = rs.getString(1);
                  String home_id = rs.getString(2);
                  String agent_id = rs.getString(3);
                  String customer_id = rs.getString(4);

                  if (!courseDataDone) {
                     xml = xml + "<sale_id>" + sale_id + "</sale_id>" +
                                 "<home_id>" + home_id + "</home_id>" +
                                 "<agent_id>" + agent_id + "</agent_id>" +
                                 "<customer_id>" + customer_id + "</customer_id>" +
                                 "" +
                                 "";
                     courseDataDone = true;
                  }

               }

               xml = xml + "</sale>" +
                           "</sales_description>";

               try {
                  SAXParser parser = factory.newSAXParser();
                  InputSource input = new InputSource(new StringReader(xml));
                  parser.parse(input, new DefaultHandler());
               } catch (ParserConfigurationException e) {
                  throw new ServletException(e);
               } catch (SAXException e) {
                  throw new ServletException(e);
               }

               response.setContentType("text/xml;charset=UTF-8");
               out.write(xml);

            } catch(Exception ex) {
               out.println("Error performing query: " + ex);
               con.close();
               return;
            }

         } catch(Exception ex) {
            out.println("Error performing DB connection: " + ex);
            return;
         }

   }
}

<?xml version="1.0" encoding="UTF-8"?>

response.setContentType("text/xml;charset=UTF-8");
PrintWriter writer = response.getWriter();
writer.append("<?xml version="1.0" encoding="UTF-8"?>");
writer.append("<sales_description>");

try (
    Connection connection = dataSource.getConnection();
    Statement statement = connection.createStatement();
    ResultSet resultSet = statement.executeQuery("SELECT sale_id, home_id, agent_id, customer_id FROM sale");
) {
    if (resultSet.next()) {
        writer.append("<sale>");
        writer.append("<sale_id>").append(resultSet.getString("sale_id")).append("</sale_id>");
        writer.append("<home_id>").append(resultSet.getString("home_id")).append("</home_id>");
        writer.append("<agent_id>").append(resultSet.getString("agent_id")).append("</agent_id>");
        writer.append("</sale>");
    }
} catch (SQLException e) {
    throw new ServletException(e);
}

writer.append("</sales_description>");

package badservlet.model;

public class Sale
{
    private String saleId;
    private String homeId;
    private String agentId;
    private String customerId;

    public Sale(String saleId, String homeId, String agentId, String customerId)
    {
        if ((saleId == null) || (saleId.trim().length() == 0)
            throw new IllegalArgumentException("sales id cannot be blank or null");
        if ((homeId == null) || (homeId.trim().length() == 0)
            throw new IllegalArgumentException("home id cannot be blank or null");
        if ((agentId == null) || (agentId.trim().length() == 0)
            throw new IllegalArgumentException("agent id cannot be blank or null");
        if ((customerId == null) || (customerId.trim().length() == 0)
            throw new IllegalArgumentException("customer id cannot be blank or null");

        this.saleId = saleId;
        this.homeId = homeId;
        this.agentId = agentId;
        this.customerId = customerId;
    }

    public String getSaleId()
    {
        return saleId;
    }

    public String getHomeId()
    {
        return homeId;
    }

    public String getAgentId()
    {
        return agentId;
    }

    public String getCustomerId()
    {
        return customerId;
    }

    @Override
    public String toString()
    {
        return "Sale{" +
               "saleId='" + saleId + ''' +
               ", homeId='" + homeId + ''' +
               ", agentId='" + agentId + ''' +
               ", customerId='" + customerId + ''' +
               '}';
    }
}

package badservlet.persistence;

import badservlet.model.Sale;

import java.sql.SQLException;
import java.util.List;

public interface SaleDao
{
    List<Sale> find() throws SQLException;
}

package badservlet.persistence;

import badservlet.model.Sale;

import javax.sql.DataSource;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;

public class SaleDaoImpl implements SaleDao
{
    private static final String SELECT_ALL_SQL = "SELECT sale_id, home_id, agent_id, customer_id FROM sale";

    private Connection connection;

    public SaleDaoImpl(Connection connection)
    {
        this.connection = connection;
    }

    public SaleDaoImpl(DataSource dataSource) throws SQLException
    {
        this(dataSource.getConnection());
    }

    public List<Sale> find() throws SQLException
    {
        List<Sale> allSales = new ArrayList<Sale>();

        Statement st = null;
        ResultSet rs = null;

        try
        {
            st = this.connection.createStatement();
            rs = st.executeQuery(SELECT_ALL_SQL);
            while (rs.next())
            {
                String saleId = rs.getString("sale_id");
                String homeId = rs.getString("home_id");
                String agentId = rs.getString("agent_id");
                String customerId = rs.getString("customer_id");
                Sale sale = new Sale(saleId, homeId, agentId, customerId);
                allSales.add(sale);
            }

        }
        catch (SQLException e)
        {
            e.printStackTrace();
        }
        finally
        {
            try { if (rs != null) rs.close(); } catch (SQLException e) { e.printStackTrace(); }
            try { if (st != null) st.close(); } catch (SQLException e) { e.printStackTrace(); }
        }

        return allSales;
    }
}

package badservlet.xml;

import badservlet.model.Sale;
import org.jdom.Document;
import org.jdom.Element;
import org.jdom.transform.JDOMResult;

import javax.xml.bind.JAXBException;
import javax.xml.transform.Result;
import java.util.List;

public class SaleUnmarshaller
{
    public void unmarshal(Object object, Result xml) throws JAXBException
    {
        List<Sale> allSales = (List<Sale>) object;
        Document document = new  Document(new Element("sales"));
        for (Sale sale : allSales)
        {
            Element child = new Element("sale");
            child.setAttribute("id", sale.getSaleId());
            child.addContent(new Element("home", sale.getHomeId()));
            child.addContent(new Element("agent", sale.getAgentId()));
            child.addContent(new Element("customer", sale.getCustomerId()));
            document.addContent(child);
        }

        JDOMResult result = new JDOMResult();
        result.setDocument(document);
        xml = result;
    }
}

FirstSaleIDFirstHomeFirstAgentFirstCustomerSecondSaleIDSecondHomeSecondAgentSecondCustomer...

|sale_id | home_id | agent_id | customer_id |
|   1    |    10   |  100     |   1000      |
|   2    |    20   |  200     |   2000      |
|   3    |    30   |  300     |   3000      |

1010100100020003000