Re: Scatter/Gather in Java or Javascript & html (Dynamic class loading?)
Richard Maher wrote:
The immutables are: -
1) I'm running in a Web browser and and am using a combo of html and
Javascript for the user interface.
2) There is an Applet that has established and authorized a Socket
connection back to a non-Java server
3) Data/Messages are exchanged in the form of Byte Arrays (ie Records)
4) The customer doesn't want to "Just do it all in Java" :-)
5) I am not interested in hearing about XDR or IDL, and if a given
application wants to use XML then good-luck to them, I will not stop them,
but for those of you left who are willing to think outside of the box,
please continue.
An example of what might happen is, the user enters an Employee Number and
as part of the validation a "Get Employee" message is sent to the server and
in response either an "Employee Details" or an "Error" message will be
returned. (For argument's sake let's adopt the convention that the first two
bytes of the message will be reserved for Message Id follow by a
message-specific body. "10" is Employee request, "11" is Employee Details
response and "99" is Lookup Error)
Anyway, if a "11" message comes back then we know 200 bytes of data will
follow which might have a Surname in a specific Character set, an integer
(little-endian) for base salary, and all the other crap that we all have.
Am I correct in assuming that there is simply no way that Javascript, and
its "var =" semantics, can deal with the complexities of character-set an
integer-endian issues, and that one must call back to Java-proper with the
document.applet.method() functionality?
There are certain possibilities in JavaScript, but I would do that
part in Java.
The problem I'm faced with now is that I'm the infrastructure/middleware guy
and I have no idea about an individual or specific Application's message
passing and formatting requirements. I have established an application
neutral, or generic, link to the host and authorized application access and
I have made available the conduit for interacting with the server code, but
I simply don't know what your subsequent messages will look like or what
they with contain. I give you a read method and a write method (and a
lovely sendUrgentData() method) but you have to provide the Class for
packing and unpacking the messages :-( How do I make your lovely
application-sepcific scatter/gather methods available to your Javascript/htm
when I insist on controlling/owning the Applet?
You could extend your protocol to be flexible enough to convert
to and from a text format.
What you have now is:
applet->server:
10 (req emp info)
177 (emp id)
server->applet:
11 (resp emp info)
"Jones" (name)
80000 (salary)
or:
99 (resp err)
And that info is really not that easy to do js->applet and applet->js.
But look at:
js->applet:
"rec=10,narg=1,arg1=177"
applet->sever:
10 (req emp info)
1 (# args)
1 (type = int)
177 (int value)
server->applet:
11 (resp emp info)
2 (# args)
2 (type = string)
"Jones" (string value)
1 (type = int)
80000 (int value)
or:
99 (resp err)
0 (# args)
applet->js:
"rec=11,narg=2,arg1='Jones',arg2=80000"
or:
"rec=99"
The JavaScript guys should not have any problems formatting and
parsing those strings.
You can come up with a zillion different formats. But a single
method in the Java applet that receives a string as argument and
return a string with data packed in some format should work.
And the wire overhead is not that big.
Can my Applet dynamically load a Class? If I get an Applet Parameter that
says PAYROLL can I not load codebase()payroll.class? OK, forget about my
applet loading the PAYROLL class; is there another way for the
Application-specific programmers to load their PAYROLL class into the JVM
and make them available to Javascript/html (who in turn will call my
send/recieve)?
> Perhaps a second Applet? How do they know about each other? Is there
> something in DOM that let's them share context? Is dynamic scripting the
> answer?
You applet can easily load a class from the server.
The JavaScript code could generate a new applet tag, but
I think that could get messy.
Let the JavaScript send something to the Java applet that makes
it load a class from the serfer, if that is what you want.
PS. I really like the look of nio sockets and the endian and charset
qualities of the buffers! But I have taken good advice and have stuck with
the IO class and .net sockets. I am using getbytes(charset) for strings and
will REVERSE() work the endian magic or will I have to do that myself?
Data*Stream also looked good! (But only if they talk to each other, right?)
DataInputStream/DataOutputStream always uses net order (big endian).
If you use them for byte arrays and 2/4/8 byte integers, then any
C sprogrammer should be able to communicate with them. Just avoid
using them directly for strings (instead you send 1 or 2 bytes
with length and N bytes with the bytes from the string).
PPS. It's a bit scary that I haven't stumbled across a Scaled Integer
class/primitive/necessity! Please don't tell me that Java uses floating
point primitives for Money. (Note to self: - What does Number class do?)
It does not.
java.math.BigDecimal is what you are looking for.
java.lang.Number is a base class for various classes containing
numeric values.
Arne