applet与servlet实时数据交互的问题

Question

//Import Servlet Libraries
import javax.servlet.*;
import javax.servlet.http.*;//Import Java Libraries
import java.util.*;
import java.sql.*;
import java.io.*;public class DbServlet extends HttpServlet {   Connection dbCon;   public void init() throws ServletException {      try {
         Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
         String dbURL = "jdbc:odbc:projects";
         dbCon = DriverManager.getConnection(dbURL);
      } catch (Exception e) {
         System.out.println("Database connect failed (init)");
         System.out.println(e.toString());
         return;
      }
   }   public void doGet(HttpServletRequest req, HttpServletResponse res)
      throws ServletException, IOException {      PrintWriter out = res.getWriter();
      res.setContentType("text/html");      String qry = req.getParameter("qry");      try {
         Statement s = dbCon.createStatement();
         ResultSet rs = s.executeQuery(qry);
         while (rs.next()) {
            out.println(rs.getString(1) + " -  " + rs.getString(2));
            out.println(rs.getString(3));
            out.println ("");
         }
      } catch (SQLException e) {
         System.out.println(e.toString());
         return;
      }
      out.println();
      out.close();
   }   public void destroy() {      /* Close database connection */
      try {
         dbCon.close();
      } catch (Exception e) {
         System.out.println("Error closing database (destroy)");
         System.out.println(e.toString());
      }
   }
}
////////////////////////////////////////////////////////
import java.awt.*;
import java.applet.*;
import java.awt.event.*;
import java.io.*;
import java.net.*;public class DbApplet extends Applet implements ActionListener {   TextField tfQuery;
   TextArea taResults;
   Button btnExecute;   public void init() {       Panel p1 = new Panel();
      p1.setLayout(new FlowLayout(FlowLayout.LEFT));      p1.add(new Label("Query String:"));      tfQuery = new TextField("", 50);
      p1.add(tfQuery);      btnExecute = new Button("Execute Query");
      btnExecute.addActionListener(this);
      p1.add(btnExecute);      add("North", p1);      taResults = new TextArea(10, 80);
      add("Center", taResults);
   }   public void executeQuery() {      String qryString = tfQuery.getText();      try {
         /* The line below can be adjusted to your local servlet position */         URL url = new URL("http://localhost:8080/servlet/DbServlet");
         String qry = URLEncoder.encode("qry") + "=" + 
                             URLEncoder.encode(qryString);         URLConnection uc = url.openConnection();
         uc.setDoOutput(true);
         uc.setDoInput(true);
         uc.setUseCaches(false);
         uc.setRequestProperty("Content-type", 
                             "application/x-www-form-urlencoded");
 
         DataOutputStream dos = new DataOutputStream(uc.getOutputStream());
         dos.writeBytes(qry);
         dos.flush();
         dos.close();         InputStreamReader in = new InputStreamReader(uc.getInputStream());
 
         int chr = in.read();
         while (chr != -1) {
            taResults.append(String.valueOf((char) chr));
            chr = in.read();   
         }
         in.close();      } catch(MalformedURLException e) {
         taResults.setText(e.toString());
      } catch(IOException e) {
         taResults.setText(e.toString());
      }
   }
   public void actionPerformed(ActionEvent ae) {
      executeQuery();
   }
}