Re: [Jscheme-devel] passing parameters to JScheme servlets

[Timothy J. H. <ti...@cs...>]

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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