Wednesday, February 17, 2010

Use your favorite Atom reader to view CXF logs

Andy Michalec and myself have worked recently on the Atom-based logging feature. Andy has implemented all the base classes and a push-style feature as well as wrote the initial draft describing how the push-style logging works. Myself has contributed recently by adding the initial code for supporting a pull-style logging.

Here is some more information about these features. They haven't made it into 2.2.6 nor will they make it into 2.2.7, etc but rather stay on the 2.3-SNAPSHOT trunk given that their code has been moved from the jaxrs frontend to a new rt-management-web component available on the trunk only.

I reckon the push style feature is already quite functional, you can try it by downloading a 2.3-SNAPSHOT and 'attach' AtomPushBeans to your jaxws or jaxrs endpoints by listing the loggers used by your code, as documented on the wiki. You may also find these links of interest :
and JAXRSAtomLoggingPushSpringTest, plus non-Spring JAXRSAtomLoggingPushTest and batch You can have log entries wrapped in a number of ways, as feeds or entries, with the content being added as an explicit entry content or an entry extension. Processing such entries is easy on the client side, with CXF you can do xmlSource.getNode('atom:entry/atom:content/*', LogRecord.class) or xmlSource.getNodes('atom:feed/atom:entry/atom:content/*', LogRecord.class).

Before actually moving to describing the pull-style feature, I'd like to mention that CXF can transparently ensure that Log4J or SL4J events can be captured back into JUL log records so you can get non-JUL records pushed/pulled as well.

Now, just today, I've finalized the first cut of the pull-style logging feature and I'm actually quite excited with the fact I was able to get a link to an endpoint-specific log feed from the CXF services page and see the list of log entries in Firefox, IE and a standalone Atom reader, by traversing to individual log entries (not in IE though which does not seem to recognize alternate links). Give it a try please, you actually might like it and it is very easy to try :-) !

Have a look at this beans.xml (see an atomPullServer bean which 'attaches' itself to a 'resourceServer' endpoint and relies on an 'atomServer' endpoint to expose the log entries) and the JAXRSAtomLoggingPullString test (see testFeed()). You will also need to add a dependency on the rt/management-web.

Some more details about the AtomPullServer. By default it is set to display 40 entries per page and keep 500 records in memory. It uses 'previous', 'next', 'last' and 'first' links to let users traverse across the whole range. The problem here is that I don't know of atom readers supporting these link types, let me know please if you do. Perhaps you do a simple atom browser yourself or easily deal with these links programmatically. May be we even add a basic browser in CXF over time.

You can inject into it a ReadWriteLogStorage implementation which can be used to offload the records to the external storage and persist them after restarts. Or just register a ReadOnlyLogStorage if you do not want your logging runtime to generate duplicate records if they're already being saved to an external file. At the moment, the latter storage requires a bit more effort as you'd need to write a file parser but it's doable and we may add few helpers later on. ReadOnlyLogStorage relies on the SearchCondition, stay tuned on the updates about using it in a regular JAXRS application code. Note that even if you already log to a file, you can still use the AtomPullServer to capture the most important log entries, there will be few of them in a healthy system so you can probably just set the max in memory size to 1000 and not worry about reading the same events from a file...

So this is what we have at the moment, give it a try please and help us to improve this feature.

Enjoy !

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