java编译时提示 javax.io不存在

package org.apache.jsp.CH3; 
import javax.servlet.*; 
import javax.servlet.http.*;
import javax.io.IOException;
import javax.io.PrintWriter;
public class HelloS extends HttpServlet{    public void init(ServletConfig config) throws ServletException
    {
     super.init(config);
    }
    public void doGet(HttpServletRequest request,HttpServletResponse response) 
    throws ServletException,IOException {         response.setContentType("text/html;charset=GB2312"); 
         PrintWriter out=  response.getWriter();
         out.println("<html>");
         out.println("<head><title> HelloServlet</title></head>");
         out.println("<body>");
         out.println("Hello World <br>"); 
         out.println("大家好 <br>"); 
         out.println("</body>");
         out.println("</html>");
         out.close();
    }
    public String getServletInfo(){
     return  "Hello Servlet Information";
    
    }
}
我的程序就是上面的,javac编译的时候提示软件包 javax.io不存在?我前面已经把j2ee.jar和servlet-api.jar放到\Java\jdk1.6.0_05\jre\lib\ext下面了简单问题,