Jun 06 2010

Ivy Dependency Management – Lessons Learned and Ant 1.8 Mapped Resources

Category: Continuous Integration,Software DevelopmentPhil @ 1:59 pm

I have been using Ivy for a couple of years now. Strangely, of all of the developers that I have introduced Ivy too, I think I’m the only one really jazzed by this approach. Some actually question the value of the tool; change is a hard thing! I think it is hard to see the real value of dependency management, especially when you only work on a single application, for an extended period of time. After all, once an application is wired up with the right libraries, what is the big deal? I tend to work on multiple projects and take a more board view of development issues. I seem to be the guy creates the Ant scripts,  upgrades the libraries, and manage the dependencies between all of these tools; hence I’m a huge fan of dependency management! I see no better way to document the external dependency requirements of an application. From a corporate or even organization perspective, Ivy can provide additional value beyond development, it can support both compliance and configuration management activities. The value of a single, centrally managed, browsable repository of reusable components should not be overlooked. I believe that significant number of person-hours are lost each year on the simple task of component (open source and commercial) version management. Just think about the amount of time spent by a project to download new component versions (and their dependencies), update build scripts, manage them in a version control system, creating tags and branches for items that never change! Now, multiple that effort by the number of applications your company manages. I have to imagine this amount of time is more than insignificant. OK, my Ivy sermon is over; on to something that might actually be valuable.

Once you have your repository structured, Ivy works pretty well. Converting an Ant-based application to use Ivy is pretty trivial and always seems to work perfectly. On the other hand, the IvyDE plug-in has always been a little bit of pain, especially when you are working with a WTP project. After converting the first project to use Ivy, it was basically a cut and paste exercise for every other project. Unfortunately, there were a few side effects of using Ivy that I just finally got around to addressing. Not that these were huge issues, more a matter of cleanliness.

Use multiple Ivy configuration files rather than one single file.

We always use a single Ivy configuration file per project; it contains the dependencies for all activities: compiling, execution, jUnit, Clover, FindBugs, PMD, Checkstyle, etc. This made the Ivy configuration a little difficult to comprehend, as it was not 100% obvious which libraries were actually required to simply build the application. Additionally, this made the Ant build files and file system rather messy; we ended up with hundreds of jar files in the Ivy retrieve directory, not knowing if a tool or component was dependent on them.  If the project happened to create a WAR file, we had to “hand pick” the files from the retrieve directory and provide a custom fileset of required files for the WEB-INF/lib directory. This was a continual maintenance issue, as someone would add a new dependency to Ivy and forget to update the custom path object in the Ant XML. To simplify and eliminate this problem, we decided to create two Ivy configuration files, one for the required components (ivy.xml), and one for the continuous integration / build environment (ivy.tools.xml).  It was now much easier to visualize and manage the run-time components required to execute the application, independently from components needed to build and/or test the application.

Use Ivy resolve Ant task rather than Ivy retrieve task, or better yet, use the Ivy cachepath task.

The simplest Ivy strategy is to dump all the components into a single directory using the Ivy:retrieve Ant task. This approach gives direct access to the files and enables the creation of multiple filesets for specific uses. This is the easiest way to convert an existing project to Ivy, just re-point the build scripts to the new location. This approach aggravated some developers on the team, as we could end up with the same jar file in at least 3 different sub-directories on your machine; a copy in your Ivy cache, another copy in the Ivy retrieve directory, and another copy in the required location (WEB-INF/lib for example). The IvyDE plug-in uses files directly from the Ivy cache, no extra copies of the files are created. I should have picked up on this approach sooner, as it seems much more elegant. There are several post resolve tasks that can be used to implement this approach, namely the Ivy:cachepath task. This task creates Ant path objects with direct references to the file’s location within the Ivy cache. If you need a fileset object, you can utilize the Ivy:cachefileset task.

As you can see from the following example, it is easy to create multiple path objects from within your Ant build process. It is even possible to have extremely fine grain control, you can create path objects for individual modules, one for each specific tool if you so desired; I  have not used this strategy yet, but it does seem interesting.

<ivy:settings file="ivysettings.xml" />
<ivy:cachepath pathid="classpath.CORE" conf="runtime" resolveId="CORE" file="ivy.xml" />
<ivy:cachepath pathid="classpath.CI" conf="runtime" resolveId="CI" file="ivy.tools.xml" />
<ivy:cachepath pathid="classpath.COMMON"organisation="beilers.com" module="common" revision="1.0" inline="true" conf="debug" />

Once you have your path objects created, you can use them just like normal in other tasks, nothing special here. It is that point that what makes Ivy so attractive from a build (Ant) perspective, in that Ivy does not require you to change the way you think or typically use Ant.

<javac source="1.5" destdir="${build.dir}" debug="${javac.debug.option}" verbose="no">
     <compilerarg value="-Xlint:unchecked" />
     <src path="src" />
     <classpath>
           <path refid="classpath.COMMON" />
           <path refid="classpath.CORE" />
           <path refid="classpath.CI" />
      </classpath>
</javac>

I did run into one issue with the Ant <war> task using the Ivy:cachepath task. When the WAR file was created, the WEB-INF/lib directory did not get flattened. All of the dependent jar files were placed in sub-directories that mirrored the Ivy repository structure. Unfortunately, the <war> task <lib> section does not support the “flatten” option. (An Ant bug was actually filed in 2004 for this problem.) Luckily, the post gave me the appropriate Ant way of resolving the situation, using a new feature in Ant 1.8 called mapped resources. The XML seems a little convoluted looking, but works perfectly. I don’t think I would have ever figured this out without Google!

By combining all of these ideas into the Ant build build system, I can take advantage of the Ivy cache and eliminate all extraneous copies of jar files. The real value is provided by the multiple Ivy configuration files, making it completely unnecessary to know what jar files are included in each dependency. This approach makes the Ant build system significantly less error prone and eliminates all future maintenance concerning  jar files.

<war destfile="${war.full.path}" webxml="WebContent/WEB-INF/web.xml" manifest="${manifest.path}">
    <fileset dir="WebContent">
     </fileset>
    <classes dir="${build.dir}"/>

    <mappedresources>
      <restrict>
        <path refid="classpath.CORE"/>
        <type type="file"/>
      </restrict>
      <chainedmapper>
        <flattenmapper/>
        <globmapper from="*" to="WEB-INF/lib/*"/>
      </chainedmapper>
    </mappedresources>

    <zipfileset dir="src" prefix="WEB-INF/classes">
         <include name="**/resources/**/*.properties" />
         <include name="**/resources/**/*.xml" />
    </zipfileset>
</war>
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3 Responses to “Ivy Dependency Management – Lessons Learned and Ant 1.8 Mapped Resources”

  1. Mark says:

    Why use multiple files? I just use multiple configs. I’ve got one config for each major subsystem, one for runtime, one for tests, one for build tools themselves. Then I just use ivy:cachepath to get create classpathes for each item, and only “retrieve” the runtime configuration. The only serious minus to this is it means I have to run ivy as part of every build. but as long as I have it configured to cache “latest” versions (so it doesn’t have to constantly talk to the server) it only takes about 10 seconds to resolve all my dependencies, and I’ve literally got more than 100, and close to 200 when you include transitive deps (yes, the project is a mess :) ).

  2. Mark says:

    Damn, shoulda finshed reading the post :)

    Although i’m still not sure I’d separate them. The build stuff seems obvious enough, but there aren’t a lot of them. The test stuff is less clearly seperated. Some if my test dependencies are clearly seperate (junit) but many are a result of what the code itself is using (say communications libraries). The only thing I can think of is having build tools as one (tiny) ivy file, the main app as a second, and the test deps as a third, with it depending on the “runtime” config of the main one, but that obviously isn’t what you’re doing.

  3. tim says:

    you can also use cachefileset:

    then in the war task add the following:

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