[JFreeChart] graphes vide

Bonjour,

je travaille sur un projet qui trace des graphes à partir des données stockés dans une base de donnée Mysql. je dois afficher dans le graphe de type BarChart qui montre le montant saisie par trimestre et par lieu.

Le problème c'est une fois que je lance la servlet , il me donne en résultat un graphe vide ! c'est comme il trouve pas les données!

voilale code de servlet:
Code:
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import java.io.File;
import java.io.IOException;
import java.io.OutputStream;
 
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
 
import org.jfree.chart.ChartFactory;
import org.jfree.chart.ChartFrame;
import org.jfree.chart.JFreeChart;
import org.jfree.chart.plot.PlotOrientation;
import org.jfree.data.xy.XYDataset;
import org.jfree.data.xy.XYSeries;
import org.jfree.data.xy.XYSeriesCollection;
 
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
 
import org.jfree.chart.ChartFactory;
import org.jfree.chart.ChartUtilities;
import org.jfree.chart.JFreeChart;
import org.jfree.chart.plot.PlotOrientation;
import org.jfree.data.category.CategoryDataset;
import org.jfree.data.category.DefaultCategoryDataset;
 
/**
 * Servlet implementation class ServletBarChart
 */
public class ServletBarChart extends HttpServlet {
	private static final long serialVersionUID = 1L;
 
 
 
 
    /**
     * @see HttpServlet#HttpServlet()
     */
    public ServletBarChart() {
        super();
        // TODO Auto-generated constructor stub
    }
 
	/**
         * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
         */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
 
		Connection conn=null;
		Statement stmt;
 
	    try
	    {
	        Class.forName("com.mysql.jdbc.Driver"); 
	        conn= DriverManager.getConnection("jdbc:mysql://localhost:3306/bd_douanes","mysql","mysql");
 
	        System.out.println("Connexion établie");
	    }
	    catch (Exception ex)
	    {
	        ex.printStackTrace();
	    }
 
	    	DefaultCategoryDataset dataset = new DefaultCategoryDataset();
	    	try {
				 stmt = conn.createStatement();
				 ResultSet rs1, rs2, rs3, rs4;
					try {
						rs1 = (ResultSet) stmt.executeQuery("select sum(totalsaisie) as 'Trimestre1' ,userlieuaff from saisie where dateconstat  BETWEEN '2011-01-01' and '2011-03-31' group by userlieuaff ;");
						rs2 = (ResultSet) stmt.executeQuery("select sum(totalsaisie) as 'Trimestre2' ,userlieuaff from saisie where dateconstat  BETWEEN '2011-04-01' and '2011-06-31' group by userlieuaff ;");
						rs3 = (ResultSet) stmt.executeQuery("select sum(totalsaisie) as 'Trimestre3' ,userlieuaff from saisie where dateconstat  BETWEEN '2011-07-01' and '2011-09-31' group by userlieuaff ;");
						rs4 = (ResultSet) stmt.executeQuery("select sum(totalsaisie) as 'Trimestre4' ,userlieuaff from saisie where dateconstat  BETWEEN '2011-10-01' and '2011-12-31' group by userlieuaff ;");
 
 
			 	    while((rs1.next())|| (rs2.next()) ||(rs3.next())||(rs4.next()) ){
 
			 	    	String v1=rs1.getString("userlieuaff");
			 	    	double v2=rs1.getDouble("Trimestre1");
			 	    	dataset.addValue(v2,"Trimestre 1", v1);
			 	    	v1= rs2.getString("userlieuaff");
			 	    	v2= rs2.getDouble("Trimestre2");
			 	    	dataset.addValue(v2,"Trimestre 2", v1);
			 	    	v1= rs3.getString("userlieuaff");
			 	    	v2= rs3.getDouble("Trimestre3");
			 	    	dataset.addValue(v2,"Trimestre 3", v1);
			 	    	v1= rs4.getString("userlieuaff");
			 	    	v2= rs4.getDouble("Trimestre4");
			 	    	dataset.addValue(v2,"Trimestre 4", v1);
 
			 	    }
 
			} catch (SQLException e1) {
				// TODO Auto-generated catch block
				e1.printStackTrace();
			}
 
 
 
	} catch (SQLException e) {
		// TODO Auto-generated catch block
		e.printStackTrace();
	}	
 
 
 
	    JFreeChart barChart = ChartFactory.createBarChart("Evolution des Saisies par trimestre", "", 
	      "par Dh", dataset, PlotOrientation.VERTICAL, true, true, false); 
	    OutputStream out = response.getOutputStream(); 
	    response.setContentType("image/png"); 
	    ChartUtilities.writeChartAsPNG(out, barChart, 400, 300);
	    String path = getServletContext().getRealPath("/img");
	    File fichier = new File(path+"");
	    ChartUtilities.saveChartAsJPEG(fichier, barChart, 400, 300);
 
 
 
 
	    }
 
 
 
	/**
         * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
         */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
	}
 
}
aidez moi s'il vous plait je suis perdue !