m2eclipse plugin makes M2_REPO variable non modifiable in Eclipse

Yesterday for first time I installed m2eclipse plugin and all of a sudden projects failed to compile. I was using Maven for quite long time hence adding all library dependencies for a project using a variable named M2_REPO, which was pointing towards a location where Maven downloaded jars were stored. After installation of m2eclipse plugin Eclipse was not able to resolve the absolute path of the jars in classpath.



The value of the M2_REPO variable was changed itself to some path other than what I configured. When I tried to fix that, to my surprise I can't edit it any longer. It was marked with this text "M2_REPO (non modifiable)". After poking here and there for a while I come to know that m2eclipse picks the value of M2_REPO variable from $MAVEN_HOME/conf/settings.xml (MAVEN_HOME is the currently selected Maven installation) file using <localRepository> element-

<localRepository>PATH_TO_REPOSITORY</localRepository>

If nothing is specifed in settings.xml then ${user.home}/.m2 directory becomes the value of M2_REPO variable.

Remove old images of Linux (Ubuntu) kernel

Development of Linux is quite fast paced and new versions of kernel are released pretty frequently. I have a dual boot desktop with Ubuntu and Windows XP. With each update grub boot menu keeps on growing and I have to make Windows XP default OS as desktop is used by my 8 year son as well. Each version of kernel takes up > 100MB space, though that is not a big worry with huge storage available at much cheaper price.

The unused (older) versions of kernel can be removed safely. Usually I prefer to keep the last version along with "last - 1", to be on safer side so that I have something to fallback upon if something goes wrong with the latest kernel. To remove a version of kernel go to Synaptic Package Manager and search for linux-image and select the ones you want to remove.



You'll get an option to remove completely (Mark for Complete Removal), that will get rid of everything including configuration files used by that package. Before removing kernel make sure to not remove the current version as that will make the system unusable. Use uname -a command to know the currently used version of kernel. Output of this command looks like below on my machine-

vinod@vinod-desktop:~$ uname -a
vinod@vinod-desktop:~$ Linux vinod-desktop 2.6.31-19-generic #56-Ubuntu SMP Thu Jan 28 02:39:34 UTC 2010 x86_64 GNU/Linux

You can also find and remove linux-headers using this simple method.

Share a datasource among several applications in Tomcat using Atomikos

In a previous post I discussed about how to use Atomikos JTA implementation in Tomcat. We had a requirement of sharing a globally defined datasource among several applications deployed in Tomcat container. The datasource lookup from the one application (whichever does the lookup first) succeeds but it always fails from the second application with an error message like-

Another resource already exists with name DATA_SOURCE_NAME - pick a different name

Why? We were using the sample bean factory available at Atomikos' site, which tries to recreate the datasource on each lookup. Within an application one can cache the datasource after initial JNDI lookup call. But what about doing a lookup of same resource from multiple applications?

After poking around for a while in Atomikos source code I found that after creation, datasource instance is cached by the Atomikos. With a minor modification in bean factory as shown below, the cached instance can be retrieved instead of recreating it.

// see if this DataSource is already initialized then return cached object
// if available, else Atomikos will throw an exception
try {
    bean = IntraVmObjectRegistry.getResource(((AbstractDataSourceBean) bean).getUniqueResourceName());
    if (log.isInfoEnabled())
        log.info("Returning cached value of AbstractDataSourceBean (Atomikos): " + bean);

    return bean;
} catch (NameNotFoundException nfe) {
    // OK, it is not available go ahead and create one
}

With this change a globally defined datasource can be used by multiple applications inside a Tomcat container to use Atomikos JTA implementation.