That scriptlet goes in a JSP. So, you have to have a page with a
form action that submits to the JSP with the scriplet in it, then
after the scriptlet executes you can display a "Thank you" or send
the user to a "Thank you" page.

BTW, you may want to use mail.jar and activation.jar instead of
the undocumented sun classes because you can't count on the sun
classes to be there in upcoming JDK releases.

Actually, I use one page for the form (.html), and then one page as the form
handler (.jsp). Keeps it simple for me to debug and the like.
Plus, sometimes I use a bean as the handler. This code would go in the
handling page, either as is or made into a bean.
I can post the bean if you'd like.

Note that the sun classes are not documented and may not be in upcoming
releases. If you like them, be prepared to grab the jar from an old SDK when
you upgrade.  ;)

So, you have an html page with a form and a jsp page as the action. The code
goes in the action page, not the form page, assuming you also keep them
separate. Some people put it all in one page and check the request method. I
find it harder to debug that way (or modify, such as when I changed all my
stuff to beans), but it's a personal opinion.

Here's another example, both the form and the handler, to clarify.
Note that it has been modified a bit for Usenet posting. These are snippets.
Some variables may be missing declarations or whatnot. Don't expect to just
be able to copy and paste it.  :)

from register.html:
---------------
<form name="f1" action="registerNow.jsp" method="post" onSubmit="return
validateMe(this);">
<table class="tRegistration">
  <tr>
     <th>First Name: </th>
     <td><input type="text" name="fname" size="30" maxlength="49"> </td>
  </tr>
  <tr>
     <th>Last Name:</th>
     <td><input type="text" name="lname" size="30" maxlength="49"></td>
  </tr>
  <tr>
     <th>HRID:</th>
     <td><input name="hrid" type="text" id="hrid" size="20" maxlength="10">
</td>
  </tr>
  <tr>
     <th>Phone Number: <span class="small">(555-555-5555)</span></th>
     <td><input type="text" name="phone" size="20" maxlength="20"></td>
  </tr>
  <tr>
     <th>E-mail:<span class="small"> (handle@domain.com)</span></th>
     <td><input type="text" name="email" size="30" maxlength="99"></td>
  </tr>
</table>
<table class="tRegistration">
  <tr>
     <th>Please select the workshop you'd like to attend.</th>
     <td><select name="wid">
         <option value='none' selected>-- Choose one --</option>
         <option value='first'>first</option>
         <option value='second'>second</option>
         </select>
     </td>
  </tr>
  <tr>
     <th>Would you like to attend the networking event? <span class="small">
(no additional charge)</span>
     </th>
     <td><input type="radio" name="networking" value="N">No<br>
         <input type="radio" name="networking" value="Y">Yes
     </td>
  </tr>
  <tr>
     <td align="center"><input name="reset" type="reset" id="reset"
value="Reset">
     </td>
     <td align="center"><input type="submit" name="Submit" value="Submit">
     </td>
  </tr>
</table>
<p></p>
</form>
---------------

from registerNow.jsp:
(elipses (...) means code has been snipped)

---------------

<%@ page import="sun.net.smtp.SmtpClient" %>
...

try
  {
  // get params
  hrid=request.getParameter("hrid");
  if (hrid == null || hrid.length() == 0) throw new IllegalArgumentException
("Missing field: HRID. Please go back and fill in your HRID, then try
again.");
  fname=request.getParameter("fname");
  if (fname == null || fname.length() == 0) throw new
IllegalArgumentException("Missing field: First Name. Please go back and fill
in your first name, then try again.");
  lname=request.getParameter("lname");
  if (lname == null || lname.length() == 0) throw new
IllegalArgumentException("Missing field: Last Name. Please go back and fill
in your last name, then try again.");
  phone=request.getParameter("phone");
  if (phone == null || phone.length() == 0) throw new
IllegalArgumentException("Missing field: Phone Number. Please go back and
fill in your phone number, then try again.");
  email=request.getParameter("email");
  if (email == null || email.length() == 0) throw new
IllegalArgumentException("Missing field: Email. Please go back and fill in
your email, then try again.");
  tmpString=request.getParameter("wid");
  if (tmpString == null || tmpString.equals("none")) throw new
IllegalArgumentException("Missing field: Workshop. Please go back and choose
a workshop, then try again.");
  else wid = Integer.parseInt(tmpString);
  networking=request.getParameter("networking");
  if (networking == null || networking.length() == 0) throw new
IllegalArgumentException("Missing field: Networking. Please go back and fill
in your networking choice (yes or no), then try again.");
       
...
{snipped code that looks up workshop name (wname) for param wid in database
and checks other stuff}
...

// send off mail
String ccMailRecipients = "{edited for usenet}";
String from="{edited for usenet}";
String to=email+","+ccMailRecipients;
SmtpClient client = new SmtpClient("{edited}");
client.from(from);
client.to(to);
PrintStream message = client.startMessage();
message.println("To: " + email);
message.println("Subject: Registration Confirmation");
message.println();
message.println("Attention: "+fname+ " "+lname+"\n");
message.println("Thanks for registering for the Development Conference.\n");
message.println("You have registered for the following workshop:");
message.println(wname);
tmpString = networking.equals("Y")?"are":"are not";
message.println("You " + tmpString + " registered for the optional networking
activity.\n");
message.println("To complete the registration process, you MUST pay your "+
               "$10 registration fee.");
message.println("Thanks,\nRegistration Team");
message.println();           
client.closeServer();       
%>
<p><b>Thanks for registering! </b>An e-mail should arrive in your inbox with
     further details shortly.</p>
<%
  }
  catch (Exception e)
     {
     String str = e.getMessage();
     if (str.indexOf("unique constraint") > -1)
        {
        %>
        <p class='error'>That HRID is already registered.</p>
        <%
        }
        else out.println("<p class='error'>"+str+"</p>");
     }
finally
  {
  try
     {
     if (ps != null) ps.close();
     if (conn != null) conn.close();
     }
  catch (Exception e2) {}
  }
  %>
  <p></p>
------------------

HTH