Saturday, July 4, 2015

ClassCastException on remote EJB call between EARs in Websphere 8.5

We have 2 EARs running on the same Websphere 8.5 Application Server. Each EAR is running in its own classloader. We have a service that initiates a remote EJB call to another service exists in another EAR. Stubs are being generated automatically on startup since WAS 7.
One of our teams tried to perform some clean up and reorder to their legacy classpath.
Right after this classpath clean up, we were trying to initiate a remote EJB call, but for some reason it thrown the following exception:
"...ClassCastException...unable to load ..._Stub..."
We didnt understand why this exception came up? why ClassCastException?
We realized that our Remote interfaces were not identical between the EARs and that there were missing classes in classpath. So whenever you have such an architecture (if you are still using EJBs while calling your legacy systems :)), you should make sure that your remote interfaces are identical and you dont have any missing classes in the classpath of the calling EAR.

Tuesday, March 31, 2015 Delicious ( bookmark importer

If you have ever tried to import all/part of your delicious links into, you probably had difficulties using the tool provided by Pocket. Pocket provides a tool that enables you to import your delicious bookmark but it doesnt work well and for some reason, large amount of your private and/or public links are not being imported. I've found out that it could be a parsing issue because of the exported delicious HTML file structure.
An important note by Pocket: Pocket is not a replacement for archival type bookmarking. Your list is a collection of links that you intend to view later. We strongly advise against importing thousands of items here.

Friday, March 20, 2015

Tuesday, March 10, 2015

RUNNABLE thread - It just looks normal

Its been a very interesting day. I just solved a bug that we were chasing after for quite some time. Generally, we collect failed HTTP requests to certain web services into a dedicated Message Queue. We process the messages in parallel by adding them into a fixed Thread Pool.
It worked successfully 99% of the time and happens that several threads have been started and unfortunately didn't accomplish their job.

We couldn't reproduce the issue and it could happen once a week at 5am :)

I couldn't find any exceptions in the server logs and the severs state were just fine. Performance was not affected, RAM & CPU state were normal.
By reading the logs, I knew that the thread hangs during an HTTP request but I knew that whenever there is no response it returns with the appropriate HTTP status code (i.e. 500).

In order to drill down a bit, I wanted to take a look at the JVM of the specific process and for that purpose I used jVisualVM. I couldn't identify anything special - memory state was fine, couldn't identify any deadlocks, parking threads, etc. so decided to generate a Thread Dump:

then passed through the above thread which is in a RUNNABLE state while infinitely waiting for the socket reader to finish its job.
It turn out that even though you set timeout properly (connection and socket timeouts), it can still hang in an infinite state. Since we are using the Google http client API to access several Google services, I couldnt get into the underlying connection manager to cancel the request so I had to wrap the request in a single Future<V> thread with a reasonable timeout that can force an abort to existing request and add the failed message back into the Message Queue.

Finally its all stable again...hmmm lets deal with the next challenge :)