带oracle数据库的Jfree条形图servlet代码

我是jfree chart的新手，我有以下代码，它运行时没有任何错误，但是浏览器显示了一个空白页。。不知道哪里出了问题

我正在尝试在servlet中使用jfree图表创建条形图，数据将从oracle数据库中检索

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.sql.*;
import java.util.*;
import java.io.IOException;
import java.io.OutputStream;
import javax.servlet.ServletException;
import org.jfree.data.category.DefaultCategoryDataset;
import org.jfree.chart.ChartFactory; 
import org.jfree.chart.plot.PlotOrientation;
import org.jfree.chart.JFreeChart; 
import org.jfree.chart.ChartUtilities; 



 public class BarChar extends HttpServlet {


        @Override
public void init() {
try {
  Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
  System.out.println("JDBC driver loaded");
}
catch (ClassNotFoundException e) {
  System.out.println(e.toString());
}
}


   @Override
 public void doGet(HttpServletRequest request, 
 HttpServletResponse response)
 throws ServletException, IOException {
 response.setContentType("text/html");

 OutputStream out = response.getOutputStream(); 

 try{


 Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
Connection conn =     DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:XE","FATIMAH", "FATIMAH");
  DefaultCategoryDataset bar = new DefaultCategoryDataset();
  Statement stmt = conn.createStatement();
   ResultSet r = stmt.executeQuery("select category,marks from chart_data");
   while (r.next()) 
   {
   String category = r.getString("CATEGORY");
   int marks = r.getInt("MARKS");
   bar.addValue(marks,"Mark",category);
    }



     JFreeChart BarChartObject=ChartFactory.createBarChart("Subject Vs Marks Bar    Chart","Subject","Marks",bar,PlotOrientation.VERTICAL,true,true,false);

    response.setContentType("image/png"); 


    ChartUtilities.writeChartAsPNG(out, BarChartObject, 400, 300);
     }
             catch (Exception e) {
           System.err.println(e.toString());
            }
         finally {
     out.close();
  }
}
 }

---

使用类型4驱动程序

oracle.jdbc.driver.OracleDriver

我更改了驱动程序，但是代码还没有运行，请帮助什么没有运行？有什么异常吗？代码正在运行，但当我打开浏览器时，什么也没有出现。