On 12/13/06, RNobrega <[EMAIL PROTECTED]> wrote:
gnodet wrote:
>
>
> What's you exact use case for both ? It would help finding a solution.
>
>
Use case #1: In broad terms: we're trying to deploy something today,
and perhaps "slightly" change it tomorrow without having to
re-deploy. Slight changes could be, for example, overriding properties
of beans created by spring from the xbean.xml files within the service
assemblies
For this, we have a configuration endpoint that hooks up to the
container using the propertyListener, and when it notices that the
container changed to STARTED, loads a bunch of properties from a set
of tables and (re-)configures other endpoints (is this an abuse of
spring and/or servicemix? is there a better way to achieve the same?)
How do you "reconfigure" endpoints ?
Could you do that individually for each endpoint using the EndpointListener ?
You can intercept all endpoints activation / deactivation.
Use case #2: we're fetching files using ftp. Out FTPGet endpoint
accepts a simple xml message with the url to be downloaded. The files
are on external sites not under our control; we can't, for example,
remove them, or rename them; they're quite large (100Mb) and our
servicemix is clustered. We're trying to avoid downloading the same
file over and over again; we're also not interested in downloading the
same file from two nodes at the same time.
We're trying to solve this by persisting all urls successfully
downloaded to a db table; a url is added to the table as soon as the
download starts, but is removed in case of failure (could be several
hours later). I thought about having a PersistentXPathPredicate handle
the database access part, and putting an eip filter in front of the
FTPGet endpoint. The tricky bit is the "removed in case of failure"
one:
public boolean matches(MessageExchange exchange) {
step 1) use an (injected) xpath expression to find out the string to
be persisted. In this example, the string is the url to be
downloaded, but it could be anything else
step 2) use an (injected) datasource and check whether this string
is on the table. if it is, return false
step 3) add the string to the table, and add a listener (this) to
the exchange; if the exchange fails, remove the string from
the table
}
If I understand your suggestion correctly, PersistentXPathPredicate
should implement ExchangeListener, be added to the container, and do
something when the exchange fails, correct?
This is all about using a clustered servicemix with an ftp binding, right ?
The latest ftp component (not the one included in servicemix-components),
but the jbi compliant one has a starting point to implement this.
An endpoint can be given a o.a.s.locks.LockManager. If the implementation
of this LockManager is clustered (using a database for example), two endpoints
won't be able to process the same file at the same time.
Unfortunately this does
not solve your entire problem as there are only two states, and there is no way
to determine if a given file has already been processed. I guess it could be
enhanced to use 3 states: free / processing / processed, where a processing
failure would put back the lock in the free state. Or we could just
imagine that
if the processing has been successful, no unlock happen (which should be easier
to implement).
Anyway, i think your solution could work. The EIP filter has been written for
things like that, but you may need a more dedicated duplicates remover
which would be able to change the state depending on the outcome of the
exchange processing.
I don't think using an ExchangeListener would be the best option, as you
just need to write a modified EIP filter for that.
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Cheers,
Guillaume Nodet
