Re: [INTERFACES] JDBC driver/applet question

At 15:07 +0300 on 16/07/1999, Twinsun wrote:


> Firstly, it works in Netscape but still doesn't in IE 4.x --  it downloads
> posgresql.jar on the local machine and then throws: "No siutable driver"
> exception(which differs from the exception which was thrown before).
>
> Secondly, it's a very inappropriate solution -- to force a user to wait
> while 130K of postgresql.jar is downloading to a local machine to display a
> few charts...
>
> Is there any way I can use the driver without having it on the machine where
> the applet is running?

Ahem... Repeat that question to yourself in a simplified fashion: "Can I
run a program on my computer without the code actually being on the
computer?".

Not really... Even if the code sits elsewhere, in order for the CPU to run
it it has to get the instructions somehow... That is, the download is quite
essential. At best, you could see which parts of the package are not used
by your particular applet, and remove these from the jar.

> > Applets are weird beasts - which is why I don't write them any more ;-)
>
> So no JDBC-based connections could be provided on the Web or there is some
> other methods I'm missing? I can do my charts with fetching all values using
> and then pass it as parameters to an applet, but then it wouldn't be
> JDBC-based soltion...

JDBC from an applet is a bad idea. It's possible under severe limitations
(you have to connect to the same host as where your applet is, you have to
pass the entire driver, you have to write it in such a way as to work in
all possible Browsers, and so on).

The reason you use an applet is probably for its drawing abilities. Using
JDBC just for the sake of JDBC "because it's cool" is not always indicated.
You can pass the data as parameters, or have them output from something on
the server side. We use, for charting, a set of applets called KavaChart.
  http://www.ve.com/kavachart/

These applets can get, as one of their parameters, a URL that supplies the
data to draw. This URL can be of a CGI or servlet that connects to the
database and returns the data. It's a much preferred way.

By the way, the KavaChart thing also exists in Servlet format. They create
their charts as GIFs and return the GIF image. This ensures that they can
be used in *any* browser, Java enabled or not. If you want to use JDBC,
servlets are the ideal place to do so.


Herouth

--
Herouth Maoz, Internet developer.
Open University of Israel - Telem project
http://telem.openu.ac.il/~herutma