May 11, 2009

Update to Checkstyle 5.0

Checkstyle 5 is available!

This is good news: a new version of Checkstyle is available that better supports Java 5 language features (like generics, annotations or package-info files). Additionally, some checks are cleaned up a bit, for instance concerning their parent in which they are contained. See the release notes for details.

Due to these changes, Checkstyle 5.0 is not fully compatible to previous versions 4.x – which is already indicated by the version number leap. Hence, don't expect the upgrade to be smoothly!

Nevertheless, I thought it would be time to upgrade, so here is what I did...

Step 1: Upgrade checkfile configuration

Due to the incompatabilities, I had to apply some changes to our checkstyle configuration to make it work with Checkstyle 5. To be sure I did it right, I have downloaded and used the Checkstyle binaries and checked my configuration for just a simple project. Hence, before upgrading Eclipse and Maven Checkstyle integration, I know my configuration is correct.

BTW, we are using a common checkstyle configuration file for all projects, and reference this "global" file with Maven and Eclipse in different ways:

  • With Maven, we use a custom artifact that contains nothing but our checkstyle.xml file. This in turn is included as build extension in our main base POM. See this post for more details.

  • For Eclipse, we use the "Eclipse Checkstyle Plugin" that provides a Remote Configuration option to reference the configuration file on an internal file server.

Step 2: Upgrade Eclipse Plugin

There is a new Beta-Release of Eclipse Checkstyle plugin (eclipse-cs) available on its update site At the time of writing, there are three features available:

  • Eclipse Checkstyle Plug-in – version 5.0.0-beta4
  • Eclipse Checkstyle Plug-in 4.4.x -> 5.0.0 Migration (Optional) – version 5.0.0-beta4
  • m2eclipse Maven Synchronization Plugin (Optional/Experimental) – version 0.0.3

Oh, seems there would have been some help in migrating from Checkstyle 4.4 to 5.0... Doesn't matter, I always like to see what the changes are so it's good to do it manually.

The m2eclipse Synchronization plugin is a new feature providing mechanism to synchronize Checkstyle rules and configuration between the maven plugin and eclipse-cs. Sounds really interesting... but let's do one step after the other and test this later.

So. I just installed the "Eclipse Checkstyle Plug-in" feature. Eclipse didn't recognize that this actually is an update, so you have to uninstall the previous eclipse-cs installation manually.

Why that? Well, the "package" has changed from* to net.sf.eclipsecs.*, and this applies to the feature's ID, too. Moreover, this renaming also affects the buildCommand and nature in .project files, they have to be net.sf.eclipsecs.core.CheckstyleBuilder and

Additionally, the notation for file sets has been changed: a file set previously configured as src\\main\\java\\com\\mycompany\\.* does no more match to any file; instead, it has to be the slash now like in src/main/java/com/mycompany/.*.

Okay, maybe I should have tried the Migration plugin... Anyways, after these changes everything works fine for me in Eclipse.

Step 3: Upgrade Maven Plugin

Good. Last piece is Maven, which provides the Maven 2 Checkstyle Plugin. However, the current version is 2.2 which is based on Checkstyle 4.4 by defining these dependencies:

There is an interesting way to override the plugin's dependencies pointed out by Brian Fox, but that's not going to work for us because Checkstyle versions 4.4 and 5.0 are not API compatible.

What can we do? Not much... we'll have to wait for a new version of the Checkstyle plugin that updates to Checkstyle 5. There is this Jira issue, and patches have already been provided some time ago. It's only that there seems to be no progress whatsoever... Checkstyle 5.0 is officially out since April 18th, so there is no reason to wait any longer! Create a new release (for my part, alpha/beta is fine as well) – please!!!

If you really need the plugin to be fixed now, you could checkout the plugin's sources and built your own version, applying the patch provided in the Jira issue. That works, but is nothing we want to do regularly!


  1. Actually the migration plugin is not as mighty as it would seem, it merely changes the project builder and nature references.

    It does not migrate Checkstyle configuration files from 4.4 to 5.0, that is still manual work.

    Good catch about the change of the fileset path separator to be platform independent - with 5.0.0 being in development for over a year I forgot about this change.
    I need to add this to the release notes of 5.0.0 final...

  2. @Ikoe, thanks for the feedback.

    In general, always wished the Eclipse plugins would provide a better description of what they are doing. Checkstyle migration plugin notes "...plugin which automatically converts workspace projects used with eclipse-cs 4.x.x" which maybe is a bit minimalistic.

    Anyhow, eclipse-cs plugin is doing a really great job and I really appreciate all the work done by the team!

  3. Thanks, Christoph.
    Yeah, in principle you are right, but you know the drill...
    Hacking code is fun, documentation not - even moreso when there is no one to pay you to do it...

  4. Hi,

    is there a chance to integrate Checkstyle 5 into the violations-Plugin of Hudson?

  5. Hey Patrick,

    you should ask this questions on the plugin's Wiki page ( As you can see in my yesterday's post, we are not using violation plugin, but instead the set of static analysis plugins that just scan the workspace for relevant result XML files that have been produced during the (Maven) build with whatever Checkstyle version.