Ralph Goers wrote:
Thanks for the explanation, except I'm still not clear what a
"connection name" is. See below for my 2 cents.
Grzegorz Kossakowski wrote:
The only problem is that we have no way to check if given URI contains
connection name or servlet
ID. Therefore the idea to add special sign that would remove the
ambiguousness appeared. Current
proposal are:
a) add a plus sign after servlet ID (by Reinhard)
b) add a exclamation mark at the very beginning of the path (by Vadim)
My personal preference is a plus sign but as Reinhard already pointed
out it does not matter that
much because we usually won't be using absolute URIs directly.
Yuck, yuck, yuck. (If you get the impression I don't like a or b you
are on track).
c) Use a different scheme to identify one vs the other.
In my perception this is strange too because it's more or less the same.
d) Use a different pattern. i.e "conventional" urls look like
http://authority/path where authority can be a variety of things such as
"server[:port]", "[EMAIL PROTECTED]:port]" and server can be a domain name or
an ip address. In this case, you could do something like
servlet://[EMAIL PROTECTED]/path which, if I understood you correctly.
could be abbreviated to servlet://connection/path. For servlet id you
could use the same syntax with servlet://[EMAIL PROTECTED]/path. Of
course, since I don't really know what a connection is I have no idea if
this makes sense, but it could certainly be abbreviated to
servlet://@servlet_id/path. Or use servlet://[connection][:id]/path,
although servlet://:Servlet_C/path still looks a little odd.
This doesn't solve the problem that we have to distinguish between a connection
name and a servlet name.
The servlet-service framework is based around the concept of servlets. In the
current implementation each servlet is configured using Spring as a bean. In
difference to the original servlet concept, servlet-service-fw servlets can have
connections to other servlets. This way inheritance and composition are implemented.
Now there are two situations: If you are in the context of a servlet and want to
use another servlet which is configured as connection, you can call it by this URI:
servlet:[connection-id]:[path]
e.g. servlet:some-connection:/foo/bar
However, there are also use cases that don't allow you to define all relations
to other servlets beforehand because you don't know them at the time of
development. If then there is a need for a servlet URI, you need to access that
servlet directly via its bean name:
servlet:[bean-name]:[path]
And that's the problem: Comparing both URIs you can't make a difference between
the relative and the absolute one. From here we've started our discussion about
+, ! and other signs.
+ and : characters in uri's just plain look strange, even if they are
allowed, unless they are used in a similar fashion to existing schemes.
Also, not having the // in the uri makes one wonder just what the token
before the first slash is. Everybody knows that whatever follows the
double slashes is not part of the path so it is less confusing.
Does anybody have a pointer to the discussion why double slashes are wrong in
our situation? (I remember some mail by Pier that explains why the double slash
in the Cocoon protocol is wrong but can't find it.)
-- o0o --
Now it's the time to give some description of static connection list
problem. Currently one can
define list of connection of a given servlet statically in XML config.
If you compile a block there
is no chance to add new connections to other servlets. Now, imagine
situation that you have some
application making charts and you create separate block (and servlet)
for each datasource provider.
For example, you create block that extracts some data from database
and second one that extracts
some data from mailbox. If you want to pull this data, you need to
connect to these two blocks of
course so you add them to your local connection list.
Now you can compile your application and everything will be working
fine. But what if you want to
define another datasource for your charts, for example data from some
web service? Of course you
develop a new block that downloads and transforms interesting data but
you need a way to inform your
appliction that there is a third block. The most obvious way is to add
connection to the third block
but this involves recompilation of your application!
The solution that I and Reinhard (and probably others) have in mind is
to let servlet use absolute
URIs so you don't need to define connections statically to other
block. There would be also some
discovery mechanism of available blocks, probably a generator, that
would return you a list of
blocks fulfilling particular needs. The list would contain servlet ID
of each servlet (block) so you
could reference them later on.
I hope this helps you a little bit.
I still don't quite get this connection thing.
What I don't get is why this can't just be servlet://[EMAIL PROTECTED]/path?
We would misuse the authority part of a URI for the purpose of defining the
service name.
Or better yet, why shouldn't my application just reference a bean id and
wire it to the block service in its Spring configuration (think Spring
remoting)?
See above. In some cases you don't know all the references beforehand. It's
similar to the use cases for the bean map (Spring Configurator).
--
Reinhard Pötz Managing Director, {Indoqa} GmbH
http://www.indoqa.com/en/people/reinhard.poetz/
Member of the Apache Software Foundation
Apache Cocoon Committer, PMC member, PMC Chair [EMAIL PROTECTED]
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