Sander Buskens

JDBC comments

2011-05-05T14:27:00.003+02:00

Today we deployed a new version of an application which uses a Sybase stored procedure to transfer some data across. On the first attempt to process some data we got a very interesting yet weird error in our logs when the application tried to execute this stored procedure:

SQL Error: 102, SQLState: 42000

com.sybase.jdbc3.jdbc.SybSQLException: Incorrect syntax near '@p0'.

Our log revealed the stored procedure to be called however as:

exec some_stored_procedure(3)

We figured something was probably wrong with the stored procedure so used a SQL client to perform the same call. Funnily enough the stored procedure worked just fine.

Something had to be wrong with our code yet we had not changed any code related to executing the stored procedure.

We reverted to a previous build where the error didn't occur and verified everything was working ok in that version.

We then configured log4jdbc to see the exact SQL going over the wire, ran the previous version of the application and then tried the faulty new build.

The SQL being executed was exactly the same save for one minute detail: in the new build all JDBC queries were prefixed by /* ... */ comments. Surely this couldn't be the source of the problem as all insert and update operations were being executed just fine and were also prefixed by comments.
Also we hadn't changed anything to do with emitting JDBC comments, or had we? We looked at the Hibernate config in the Spring application context file and found out that indeed hibernate.use_sql_comments had the value of 'true'.
So we changed this to false and reran the the code that triggered the stored procedure.
Everything was now working well.

I guess Sybase really doesn't like JDBC comments in combination with stored procedures ...

java.lang.LinkageError in Weblogic

2011-04-05T08:05:00.000+02:00

Yesterday I deployed a webservice which had been built by a third party on our Weblogic server.
This went fairly well apart from a few minor issues and everything was up and running faster than I'd anticipated.
After the application server and application had started I entered the endpoint URL which worked just fine, next step was to retrieve the WSDL so I could create a few simple test requests with SoapUI.
Retrieving the WSDL resulted in an error page displaying an all too familiair exception:
java.lang.LinkageError: Class javax/xml/namespace/QName violates loader constraints

I'm sure we all now about it by now but in case we don't: don't package API classes if you don't have to, as different versions are usually already on the application server classpath resulting in the exception mentioned above.

Nine out of ten times these API jars "accidentally" end up in your war/ear as they're pulled in as a Maven dependency so I make a habit of checking the war/ear from time to time (when dependencies have been added) and excluding any unwanted API jars.

In this case it turned out a version of xpp was being used that packaged this particular class, bumping up the version number solved the problem.

It's about time really

2011-04-05T07:42:00.000+02:00

So I've decided to finally start up a blog. The idea has been playing on my mind for a while and seeing more and more of my colleagues starting up blogs I figured it's about time really.

So what am I going to blog about? Mostly IT related stuff I'd say. A couple of years ago I setup this private Wiki on my dedicated server and started putting solutions to problems I'd come across in there. Going all security paranoid I secured this Wiki with 2-way SSL and needless to say a couple of years down the line the Wiki is not being maintained anymore as I've long since lost the client certificate.

So blogging about the technical problems I come across on a regular basis at work and at home will basically serve three purposes: a) I build up my knowledge base, b) it's public so I'll have a harder time locking myself out and c) from time to time the solutions I blog about will be of help to others out there which is wonderful as knowledge is there to be shared in my humble opinion.