Problem with JDBC and Tomcat

Question

I don't know where the problem originate, the only thing in my memory is that the program worked very well on my PC yesterday, but today, without even slightest change, it doesn't work anymore. As to debug it, I simplified the codes to the least, but it still refuse to work. I was beaten down by this problem totally, and cannot make out any solution for it, so, I come here, hoping to find a warrior to kill this damned bug for me.
My program is a Servlet, but for the purpose of debugging, I have recode it to an Application/Servlet. When run as a application, I can get the result expected, but as a Servlet, :-(, maybe you should see it by yourself. My server software is Tomcat 4.1.15, and the JDK version is 1.4.0. To excute this program, you should add Data Source "Test" to ODBC.
///////////////////////code begins/////////////////////////
import java.sql.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.util.*;
public class Ex extends HttpServlet
     int ErrorType = 0;
     String err = new String("");
     public static void main(String args[]) throws Exception{
          Ex cEx = new Ex();
          cEx.init();     
          System.out.println(cEx.ErrorType);     
     public void init() {
          String url = "jdbc:odbc:Test";
          ErrorType = 3;     //passed
          try{
               Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
          } catch (ClassNotFoundException e) {
               e.printStackTrace();
               ErrorType = 1; //trapped in Class.forName
          try{
               Connection c = DriverManager.getConnection(url);
          } catch (SQLException e) {
               e.printStackTrace();
               ErrorType = 2; //trapped in DriverManager.getConnection
               err = e.getMessage();
     public void service(HttpServletRequest req, HttpServletResponse res)
               throws IOException {
          res.setContentType("text/html; charset=GB2312");
          PrintWriter out = res.getWriter();
          out.println("Success " + "<p>" + ErrorType + "<p>" +err);
          out.close();
//////////////////////////code ends///////////////////////////////
The result from the Servlet tell me that the problem occurred within the connection process, I don't know who should be responsible to this - Tomcat or JDBC?

Answer 1

If you could print the exception that you got then that would help :) In the mean time, I could make a guess. It is unlikely that your application server (in this case, Tomcat) is blocking connections from your servlet. So the problem is either with JDBC directly or with the underlying datasource. It seems unlikely that it is JDBC given that you have stated that the code has not changed and it works in application form.
My guess would be that you are coming up against some sort of security constraint (eg: your DBMS is letting you log in from one IP but not another?, your Java plug-in security policy is disallowing the connection?). It's hard to say.
But if it works as an application but not via a servlet then you could try putting this in your java.policy file, which is located in the directory where your plug-ins are installed (eg: "C:\Program Files\Java\<version>\lib\security\") on Windows systems;
permission java.net.SocketPermission "bend xp:1099", "listen,connect,accept";
Try that, see if it works :)
Ben