Wednesday, September 26, 2012

JBoss and CXF: it is not over yet

I came across the Spring story some time ago but did not have time to write about it then. I would probably spend time writing about it now but recently I had to refresh my knowledge of JBoss and CXF.

Besides Spring usage, JBoss CXF integration has more nice things to offer. They are more subtle but they definitely deserve to be mentioned.

Remember that little jbossws-cxf.xml? It has its own secrets.

First of all there are several locations where JBoss WS code looks for it. Do you know where exactly the file is packaged in jar/war/whatever? If you think the correct location is META-INF/ for jars and WEB-INF/ for wars, you are close but it is only part of the story. This is the location that the WS deployer checks for jbossws-cxf.xml at application startup. Note that JBoss does not use classloading to locate this file, it goes straight to the jar/war and checks if the file is present. If it is there it is processed together with some other JBoss CXF specific deployment descriptors that the deployer can find at this moment. If no META-INF/jbossws-cxf.xml or WEB-INF/jbossws-cxf.xml is found the deployer does not look at other deployment descriptors even if they are present. This is important because whatever JBoss manages to find at this moment is used for configuration of WS services and injection of WS client references. Well, may be.

Of other places where JBoss WS deployer looks the most important is META-INF/cxf/jbossws-cxf.xml. Pay attention to that cxf in the path. JBoss: consistent as ever; flexible as nothing ever before. It gives you possibility to place config files in at least two different places. There are of course notable differences. First one is already explained above: the deployer is loading config files only if it detects META-INF/jbossws-cxf.xml or WEB-INF/jbossws-cxf.xml. Then it loads that file and also META-INF/cxf/jbossws-cxf.xml if present. So if you have only META-INF/cxf/jbossws-cxf.xml, the deployer will not see at application startup.

Another difference is that uses classloading to load a single META-INF/cxf/jbossws-cxf.xml. This, of course, is a source of some amusement if you happen to have multiple jars with META-INF/cxf/jbossws-cxf.xml. JBoss has some jars with that file already, like server/<server_name>/deployers/jbossws.deployer/jbossws-cxf-client.jar. If you also have META-INF/cxf/jbossws-cxf.xml in your application then which file is loaded depends on the classloading configuration. I do not know how important things from jbossws-cxf-client.jar are but you definitely do not want to miss your configuration.

Location is covered; time to look at the moment when JBoss looks for the file. It does it not only during application startup, as described above. If you use WS API like JBoss will do it again. Basically it is the same story except that it never loads META-INF/jbossws-cxf.xml or WEB-INF/jbossws-cxf.xml. It just goes straight to all those other JBoss CXF specific deployment descriptors that it can find, including META-INF/cxf/jbossws-cxf.xml. This process might use a different classloader than the one used during deployment so the loaded configuration might differ significantly from the one loaded during application startup.

A nice finishing touch comes from Spring XML parsing code. Most likely it is somehow configured from JBoss but I did not care to find out where and how. Deployer triggers (META-INF/jbossws-cxf.xml or WEB-INF/jbossws-cxf.xml) are parsed with XSD validation on, all other files are parsed with validation off. It seems to be a minor difference unless you want the configuration from jbossws-cxf.xml applied to the WS objects you get back from Service.create() and Service.getPort().

Basically you can use <jaxws:client> to provide custom configuration on a per-client basis, the same way as you can use <jaxws:endpoint> to configure your endpoints. But there is great confusion around <jaxws:client>: it looks like it is ignored by JBoss or CXF. For example interceptors configured on a CXF bus are used properly but interceptors configured on <jaxws:client> are not.

The reason is that you need quite crazy identification string for your <jaxws:client>. Things that are perfectly OK for <jaxws:endpoint> won't work for <jaxws:client>. Why? Because it is JBoss of course!

Some JBoss documentation suggests you have to use <jaxws:client id="{your.service.namespace}YourPortName" >. This kind of ID is not valid according to Spring XML schema. If you put it in your META-INF/jbossws-cxf.xml or WEB-INF/jbossws-cxf.xml, the application startup will fail with XSD validation error. To be fair to JBoss it looks like this particular naming convention is coming from CXF and not from JBoss.

But it is still not all! <jaxws:client id="{your.service.namespace}YourPortName" > does not work. It does not work if you rely on @Resource or @WebServiceRef, or, at least, it did not work for me when I tried, but I did not try hard. It does not work for, and I needed it to work so I wasted most of my time on this use case.

Still other sources say that <jaxws:client id="{your.service.namespace}YourPortName" createdFromAPI="true"> is a way to go. It still does not work! It took me quite some time poking in CXF and Spring code under debugger to find out the version that worked for me: <jaxws:client id="{your.service.namespace}YourPortName.jaxws-client.proxyFactory">.

Basically it is CXF that ends up looking up a Spring bean named "{your.service.namespace}YourPortName.jaxws-client.proxyFactory" to get its configuration. The funniest thing is that both versions of configuration register a bean with this name. But for whatever reason when a bean is created with createdFromAPI="true", it is registered all right but it is not found later by CXF. And if it is created with ".jaxws-client.proxyFactory" suffix it is registered and successfully found by CXF.

I stopped looking further. I found enough to make my application work. But I still wonder: how could I miss it in the beginning? Nice, intuitive, easily discoverable configuration. Unforgivable.

Friday, September 7, 2012

Assorted facts about JBoss. Fact 6: JBoss and CXF: match made in heaven.

Bored? Want to learn something new? Or waste some time? Need quality headache?

My advice: look at web services and try to make something just a bit more complicated than "hello world" under JBoss. You will never forget it.

JBoss 6 uses CXF under the hood to support WS-related sections of EJB specification. Both products have their strong points but JBoss is definitely the leader in the "most creative WTF" contest.

JBoss supports declarative configuration of both web service implementation and web service client. All you need is to create a JBoss specific deployment descriptor, a file called jbossws-cxf.xml, and package it with your application. The nice touch here is that this deployment descriptor is Spring-based. This alone makes JBoss leading contester.

It is not that I have anything against Spring. Well, I actually have a lot to say about it, but it deserves a separate post.

No, really, just think about it: first you come up with a way to configure the server using XML, supporting hundreds of different schemas, all based on the same XML configuration parser library. And then you say "screw it, I fancy Spring here".

They did not go as far as packaging Spring with JBoss. Why? Who knows. Having said A they might just well have said B. But no, they use classloading to detect at runtime if Spring is present. Only if Spring is there JBoss goes ahead and reads jbossws-cxf.xml. Wow, say good bye to all hard work you put into creating that jbossws-cxf.xml - it is not used anyway. But you do not know that yet.

After some googling and digging you realize that you need Spring. Sigh. But you do need that configuration from jbossws-cxf.xml! Being "standard obeying" you bite the bullet package Spring with your application. (Being lazy you just drop Spring into server/<server_name>/lib. You save yourself a lot of time but miss a lot of fun.) Redeploy and ... your precious jbossws-cxf.xml is not loaded.

Things are looking up: you are not bored any more. You spend some time double checking your deployment and redeploying it. Nope, still not loaded. If you study jboss logs carefully you might spot this small message Spring not available, skipping check for user provided jbossws-cxf.xml / cxf.xml configuration files. If you know your way about JBoss jmx console you go and check your application's classloader and try to load some Spring classes via it. They are loaded just fine. WTF?

Remember that runtime classloading check I mentioned above? Turns out it runs very early during application deployment, before the classloaders for the application are set up. As a result the check is using the classloader of the WS deployer coming from server/<server_name>/deployers/jbossws.deployer. Surprise!

It is getting more and more interesting. You have to have Spring and you can't package it with your application. Right, but you need to make this application work. Forget about standards and keeping things where they belong. Spring to server/<server_name>/lib, JBoss restart, wow! Congratulations, you made it.

I leave the question of the proper place for Spring jars as an exercise. Instead let's look at more fun that JBoss-CXF integration might bring.

This is how I first got involved in this matter: I had an EJB application that used JMS. For reasons not important here it was decided that the application should use Apache ActiveMQ. No problem, I tested it locally under JBoss 6.1, it looked OK, and so the application was deployed in an integration environment, together with ActiveMQ resource adapter. So far so good. Later more applications were added to that environment. One of them failed to start. There were some classloading errors involving Spring classes. The application was a war that internally used Spring so Spring was packaged into WEB-INF/lib and the classloading was properly configured (WEB-INF/lib jars first). I was asked to look into the problem because there was another Spring in classpath: from ActiveMQ which is using Spring internally.

Of course removing ActiveMQ RA solved the problem for that application. Changing classloading rules of the application (to parent first) "solved" the problem as well.

Digging further I realized what has happened. JBoss classloader architecture is notoriously broken so the Spring classes from ActiveMQ leak into every application. When this failing application (with the original configuration WEB-INF/lib jars first) was starting JBoss WS deployer noticed some WS annotations and went ahead with whatever it supposed to do, including looking for Spring and jbossws-cxf.xml. Spring was there leaked from ActiveMQ. (Remember, the classloader at this moment is the one from jbossws.deployer.) The application did not have jbossws-cxf.xml but the harm was done: some instances of Spring classes were created along the way and remained referenced from CXF objects.

The application startup continued and JBoss finally created the application specific classloader and the rest of the startup code was executed using this classloader. Along the way CXF was involved again and it noticed those Spring instances created before so it went ahead with more Spring dance. But this time all the Spring classes were coming from WEB-INF/lib with predictable result: ClassCastException.

Of course changing classloading configuration would fix the problem in this case. Spring classes would always come from ActiveMQ keeping CXF happy. Well, until some other application, RA, whatever, that has Spring packaged is deployed in the same server. And do not forget that it can be a different version of Spring jars. Care to resolve this mess?

Priceless! Never attribute to malice that which ... I am not sure. Sometimes I think somebody at RedHat came up with this brilliant business idea of how to make more money out of JBoss support ...