Revisiting Java technology on the client

import netscape.javascript.*;

class PhoneNumberValidator extends java.applet.Applet
{
  java.net.URL ServerURL = new java.net.URL(getParameter("SourceURL"));
  public boolean isValidTelephoneNumber()
  {
    try
    {
      JSObject DocumentWindow = JSObject.getWindow(this);
      JSObject HTMLDocument = (JSObject)DocumentWindow.getMember("Document");
      JSObject InputForm = (JSObject)HTMLDocument.getMember("InputForm");
      JSObject TelephoneNumberEntry = (JSObject)InputForm.getMember("TelephoneInputField");
      JSObject TelephoneHiddenField = (JSObject)InputForm.getMember("TelephoneHiddenField")
      TelephoneHiddenField.setMember("value",
                           getStandardizedTelephoneNumber(TelephoneNumberEntry.getMember("value")));
      return true;
    }
    catch(InvalidObjectException ex)
    {
      return false;
    }
  }

  // Note: there's a lot left out here in terms of Content factories
  //       the whole server-side interface, etc...
  private String getStandardizedTelephoneNumber(String IncomingNumber) throws InvalidObjectException
  {
    java.net.HttpURLConnection NewConnection = new java.net.HttpURLConnection(ServerURL);
    NewConnection.setRequestMethod("POST");
    NewConnection.setRequestProperty("TelephoneNumber", IncomingNumber);
    NewConnection.setDoInput(true);
    NewConnection.connect();
    Object ReturnedValue = NewConnection.getContent();
    if(ReturnedValue instanceof String)
      return((String)ReturnedValue);
    else
      throw new InvalidObjectException("Server Request returned an invalid object");
  }
}

The JavaScript Code on the HTML page:
<APPLET
    CODE="PhoneNumberValidator.class"
    width=0
    height=0
    name="PhoneNumberValidatorClass"
    CODEBASE="http://www.someplace.com/someapp/applets/validators.jar">
</APPLET>

<FORM name="InputForm" method="GET" action="CreateUser.jsp">
    <P>Enter a telephone number:</P>

    <INPUT TYPE="text" name="TelephoneInputField" LENGTH=20
          onChange="document.PhoneNumberValidatorClass.isValidTelephoneNumber()">

    <INPUT TYPE="hidden" name="TelephoneHiddenField" >
</FORM>