I run James on a VPS host with about 300 MB of memory. Now you are
talking about multiple machines. It sounds to me like you want to
complicate James unnecessarily to try out some new framework (that
nobody else on the list seems to get). Why should James be the Guinea
pig for some new framework? I think that the effort to "Guiceyfy" should
just continue as is.
People have talked about getting Avalon out of James for years, and
finally the Guice effort is making some progress. Now you want to throw
a wrench into everything with some new framework. Why? Let's just do one
change at a time.
Eric MacAdie
Simon Funnell wrote:
Hi,
I've been studying the code base and evaluating which approach is the
best to take. At present, I will try to clarify the framework
architecture I am using as 'evangelising' might actually be quite
effective. Firstly, there is nothing new to learn, the architecture is
exactly the same as the internet. Applications are networks of
machines and each machine on the network is a component of one or more
applications. Each machine/component specialises in doing one small
job very well, for example you could have a network of
machines/components that do something like the following.
Machine 1's job is to listen on a port for new client connections,
when a new client comes along, it is accepted and the resulting socket
is contextualised. A context is basically an object that maintains
state, such as application/session/request or whatever is relevant.
This context/state is then dispatched to Machine 2.
Machine 2 will now alter the context state by reading bytes from the
socket and buffering them in some suitable form before dispatching to
Machine 3.
Machine 3 is responsible for taking the buffered content and parsing
into some sort object model, like an email. If an error occurs this
machine will forward it to an exception handling machine which
implements the exception policy of the system (Machine 4?). Otherwise,
it is sent to the next machine (Machine 5?) which does some sort of
matching or something
And so on.
Now if we want to do some logging at any time, we just put a logging
machine in between Machine 1 and 2 or between 2 and 3 to check socket
state, buffer state or some other combination of properties.
To relate this somewhat to James, you are currently using Guice to
wire components together and.this is equivalent to defining a network.
With the design I am following there is not really a configuration as
such, they are basically replaced with policy statements and change
logs, which are a kind of configuration. Its fair to say James would
be a network of machines defined by a policy statement. These policy
statements can be large or small and applied to new or already running
systems. Newer policy statements always supersede older ones (unless a
prior policy forbids it). James already has a fairly substantial
default policy statement like thing, its configuration files. However,
to understand the benefits of policy statements, instead of
configurations, it is worth looking at a small example.
In this example I have an installation of James, it does not do any
logging at present but I want to do some. And this is what I want to do:
For the next two days, between the hours of the 3-5 pm, if a client
using the SMTP service invokes the Expn command and has a IP address
matching some address log some information to this file in this format
and if its between 3.45pm and 4.00pm send me an email with such and
such information.
This policy is expressed (but doesn't have to be) as an XML document.
The document is evaluated and the necessary machines are added to the
network to implement the policy. How the policy is defined and
implemented is system independent. The new machines added to the
network that implement the policy usually simply fit in between two
existing machines and do stuff like filtering, logging, security and
anything that makes logical sense (putting a logging machine that
records information about a http request in an smtp service doesn't
make logical sense). Here, Java is used to create very small, highly
robust units of functionality with XML policy statements (closer to
natural language and easy to learn for users) stating how the machines
should interact. The sophistication of policy statements is increased
as the size and collective ability of a community of
machines/components in a given installation grows.
The current mailets and matchers are sort of ideal for use in this
system as they can (in principle) be easily wrapped/adapted or what
not to become a network machine. A machine here is simply an object
with a single method (I've been thinking about using the reflection
api's to extract individual methods from existing James classes and
assign them to individual machines but its not straight forward as the
existing methods in James classes tend to mix concerns together, like
application logic and writing to an output in a single method)
I hope this is of interest, declarative logging is really easy to
implement and requires no learning, only a subtle shift in approach.
James could be implemented as a guice module and a policy statement,
in fact it would probably would be fairly easy to generate guice
modules from a policy statement. Its not a direct translation but they
are not dissimilar in nature. Also I am actually thinking of employing
guice myself to do a few things, I am not in competition with guice. I
am not in competition with spring either because its got a load of
stuff with it mine doesn't. That said, Platformed is not 'just another
framework', it has features (an architecture) that make it distinct.
I'm thinking about a re-factoring strategy but I am still learning
James under the hood. Ideally I would like to convince you of the
benefits, they are fairly obvious.
Regards,
Simon
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
