The Jscheme Web Programming Project

Tim can probably answer this better than i can.  Also a bit more context of what you want to do would help.

Can you put the information in a hidden field in a form?

At 02:12 PM 9/28/2004 -0400, Geoffrey Knauth wrote:
>How do I pass parameters between JScheme servlets?
>
>Geoffrey
>--
>Geoffrey S. Knauth | http://knauth.org/gsk
>
>
>
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On Sep 28, 2004, at 2:12 PM, Geoffrey Knauth wrote:

> How do I pass parameters between JScheme servlets?
There are several techniques ...
As Ken suggests, hidden parameters is a standard one
>    <input name="abc" type="hidden" value="xyz"> ..


Another approach is to use session parameters which
are stored on the server and accessible to servlets in the same session.
I do this using the following two procedures for storing and accessing
session values (which is in the jscheme webapp from CVS in
WEB-INF/scheme/servletlib/session.scm

> ;; storing session data
>  (define (session-set request N V)
>    (.setAttribute (.getSession request) N V))
>
>  (define (session-get request N Default)
>   (let ((x (.getAttribute (.getSession request) N)))
>    (if (equal? x #null) Default x)))
This approach is good for passwords where you get them once
from the user and the store them in a session attribute.

Does this help??

You could probably also "call a servlet" and get its return value by 
doing a read on a URL...
>
>   (define result
>        (http-read
>            
> "http://my.company.com:8080/jscheme/my.servlet?a=1&b=2&c=3&d=hi"))
>

but this can expose you to the danger of infinite servlet loops where 
servlet A calls servlet B
who calls servlet C, etc.

The http-read procedure can be defined as follows (but there might be a 
more elegant solution....)

> (define (http-read url-string)
>    ;; this reads a string from a given url
>    (define url (java.net.URL. url-string))
>    (define http-con (.openConnection url))
>    (define buf (java.lang.reflect.Array.newInstance char.class 65536))
>
>    (define (drain-from-in in) ;; read input lines into a list in 
> reverse order
>     (let loop ((n (.read in buf 0 65535))
>                (L ()))
>          (if (equal? n -1)
>              L
>              (let ((z (java.lang.String. buf 0 n)))
>                (loop (.read in buf 0 65535) (cons z L))))))
>
>    (define (strip-out-header L) ; L is a reversed list of lines from 
> an http file
>        (let loop ((L L) (R ()))
>          (cond ((null? L) R)
>                ((equal? (first L) "") R)
>                (else (loop (rest L) (cons (first L) R))))))
>
>    (define (list->string L)
>      (let loop ((L L) (z (java.lang.StringBuffer.)))
>           (if (null? L)
>               (.toString z)
>               (loop (rest L) (.append (.append z (first L)) "\n")))))
>
>    (let (
>           (in (java.io.BufferedReader.
>                (java.io.InputStreamReader.
>                 (.getInputStream http-con)))))
>      (let* ((result (drain-from-in in)))
>         (.disconnect http-con)
>         (list->string (strip-out-header result))
>     )))


---Tim---



>
> Geoffrey
> --
> Geoffrey S. Knauth | http://knauth.org/gsk
>
>
>
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Ken and Tim  -- Thanks for your suggestions.  What I discovered was 
close to what Ken suggested (hidden parameters), but I can see utility 
for Tim suggested (session parameters).  Here is the test code I used.

Geoffrey
--
Geoffrey S. Knauth | http://knauth.org/gsk

;;;;; send.servlet

(servlet
  ()
  (define (buttonSend buttonValue action att val)
    (sa-form (catt (s-method "post") (s-action action))
             (s-input (s-type "submit") (s-value buttonValue))
             (s-input (s-name att) (s-type "hidden") (s-value val))))
  (load "webapp/jscheme/test/html.scm")
  (buttonSend "Send my name" "recv.servlet" "firstName" "Geoffrey"))

;;;;; recv.servlet

(servlet
  ()
  (load "webapp/jscheme/test/html.scm")
  (let ((name (.getParameter request "firstName")))
    (s-html
     (s-p "Your first name is: " name)
     (go-button "again" "send.servlet"))))

Tim,

Your various servlets always read and evaluate a file, which is fine for your course and development, but what about performance?

Could we get a servlet that only reads the file once?  Or maybe even never - it calls a function that its already loaded?
k

On Sep 28, 2004, at 4:34 PM, Ken Anderson wrote:

> Tim,
>
> Your various servlets always read and evaluate a file, which is fine 
> for your course and development, but what about performance?
>
> Could we get a servlet that only reads the file once?  Or maybe even 
> never - it calls a function that its already loaded?

I haven't though much about it, but its a good idea.

A partial solution would be to write servlets as follows:
(servlet (a b c ... z)
   (use-module "/full/path/to/file/F.scm")
   (F a b c ... z)
)

The server would still have to read and parse the file, but it would be
a relatively small file.

One could also skip even this small amount of parsing by using a cache
to see if the file has been read before... (This would go in 
WEB-INF/scheme/scheme.sss)

I haven't tried either of these, but it would be interesting to see how 
much they improve
performance. (I've found httperf to be a nice tool for measuring 
servlet performance....)

---Tim---


> k
>

On Sep 28, 2004, at 4:34 PM, Ken Anderson wrote:
> Could we get a servlet that only reads the file once?  Or maybe even 
> never - it calls a function that its already loaded?

I think it should be an option.  load-always or load-once, so to speak.

At the customer site where I've been using JScheme servlets to demo 
screen designs and change them on the spot, it's been very nice that 
little tweaks to my html.scm and defs.scm "libraries" get reflected 
immediately in the browser, and fellow developers were impressed that I 
never had to stop/restart the Jetty server.

I can see the value of load-once too, so long as there is a way to dump 
("forget") something in memory dynamically so a new version can be 
loaded.

Geoffrey
--
Geoffrey S. Knauth | http://knauth.org/gsk

It would be nice be able to say something about the overhead of JScheme servlets vs Java servlets.  What results did you get from httpref?

Here's a good evaluation of different servlet containers
http://www.webperformanceinc.com/library/ServletReport/

It mentions, at the end, that Jetty does not seem to use all of the CPU in its normal configuration.

On Sep 28, 2004, at 5:18 PM, Geoffrey Knauth wrote:

> On Sep 28, 2004, at 4:34 PM, Ken Anderson wrote:
>> Could we get a servlet that only reads the file once?  Or maybe even 
>> never - it calls a function that its already loaded?
>
> I think it should be an option.  load-always or load-once, so to speak.
I agree. We can work on it.

One method I have been using for static webpages that are build using 
jscheme servlets
is to just use a website copier (e.g. wget -kmp --update-links 
http://localhost:8080/mywebapp )
and then have a script that copies the website and moves these static 
pages to an apache
server.

In the http://www.4collegewomen.org site there are both static and dynamic 
pages so I have two variables
[dcontext] and [scontext] and use the wget to copy only the static 
pages while leaving links to the
dynamic pages alone. The apache-served static pages then have links to 
the Jetty-served dynamic
pages and we get good performance on static pages and OK performance on 
dynamic pages
(which are used as often for that website).

I often work with the "founder" of the website (a public health 
professional in Washington) by
phone and as we both view the website, I make changes to the dynamic 
site, run the script to
copy it to apache, and she sees the changes almost immediately. its 
pretty cool and really easy
from this side....



>
> At the customer site where I've been using JScheme servlets to demo 
> screen designs and change them on the spot, it's been very nice that 
> little tweaks to my html.scm and defs.scm "libraries" get reflected 
> immediately in the browser, and fellow developers were impressed that 
> I never had to stop/restart the Jetty server.
>
> I can see the value of load-once too, so long as there is a way to 
> dump ("forget") something in memory dynamically so a new version can 
> be loaded.
Yes, I do this on my sites using a "reload.servlet" at the top level 
that I can call to reload the dynamic
environment that the servlets run in.  That environment is initially 
set up when the Scheme servlet is loaded
by calling some initialization code in WEB-INF/scheme/scheme.sss which 
loads in the file in
WEB-INF/scheme/servletlib/init.scm and possibly elsewhere in WEB-INF.

---Tim---

>
> Geoffrey
> --
> Geoffrey S. Knauth | http://knauth.org/gsk
>
>
>
> -------------------------------------------------------
> This SF.net email is sponsored by: IT Product Guide on 
> ITManagersJournal
> Use IT products in your business? Tell us what you think of them. Give 
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