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Karl Heinz Marbaise
Karl Heinz Marbaise

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Continuous Delivery With Apache Maven

#maven #devops #opensource

Based on todays requirements it is needed to do a continuous delivery of your artifacts by each change on your master (Git)/trunk(SVN). The question is what you need to achieve this with Maven?

Usually you are using so called SNAPSHOT versions which means your version looks like 1.2.3-SNAPSHOT and indicates that you are currently working towards the release version 1.2.3. Afterwards you continue with the next snapshot version like 1.2.4-SNAPSHOT and so on.
Depending on your environment this has been changed which means that each change you have made on master (Git) you need to produce a new release version which means 1.2.3 and next will be 1.2.4. The development will be done on branches where you might need a SNAPSHOT version.

Let us take a look into a single module pom file which looks like this:

<project
  xmlns="http://maven.apache.org/POM/4.0.0"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

  <modelVersion>4.0.0</modelVersion>

  <parent>
    <groupId>com.soebes.smpp</groupId>
    <artifactId>smpp</artifactId>
    <version>4.0.1</version>
  </parent>

  <groupId>com.soebes.examples.j2ee</groupId>
  <artifactId>domain</artifactId>
  <version>1.2.3-SNAPSHOT</version>
...
</project>
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The version is defined with 1.2.3-SNAPSHOT if you now call:

mvn clean package
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You will produce artifacts which look like domain-1.2.3-SNAPSHOT.jar. Unfortunately this kind of artifact is something which can change over the time based on Maven philosophy. That means if you now make a change in your code and just do it again mvn clean package it will create the same domain-1.2.3-SNAPSHOT.jar file. There is no real difference if you do an mvn clean install instead. This will only install the created artifact into your local cache $HOME/.m2/repository. Furthermore if you do mvn clean deploy the difference is only that each time you do this on your repository manager the naming schema is a little bit different which means the artifact will look like domain-1.2.3-20180821.202345-1.jar. So in the end the artifact contains a time stamp. But the most important thing is that SNAPSHOT versions are not immutable as you might have already realized based on the above.

So the only way to create real immutable versions is to create releases from Maven point of view. This means you have to use a version without -SNAPSHOT. So in consequence you have a pom file which looks like the following:

<project
  xmlns="http://maven.apache.org/POM/4.0.0"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

  <modelVersion>4.0.0</modelVersion>

  <parent>
    <groupId>com.soebes.smpp</groupId>
    <artifactId>smpp</artifactId>
    <version>4.0.1</version>
  </parent>

  <groupId>com.soebes.examples.j2ee</groupId>
  <artifactId>domain</artifactId>
  <version>1.2.3</version>
...
</project>
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So you can do a mvn clean deploy and you have created an immutable release artifact domain-1.2.3.jar. If you try to do this a second time your repository manager will tell you that this does not work cause by definition releases are immutable which means you can not overwrite them. So the consequence is if you have made a change/mistake/fix to your project you have to change the version number. Ok, not very complicated just change the version to 1.2.4 commit and do another mvn clean deploy? So good so far.

Some people do not like the commits where only a version has been changed. So the question is: Is there a more convenient way to handle this?

Starting with Maven 3.5.0+(I recommend to use the most recent version) there is a more convenient way to handle that. You can write your pom file like the following:

<project
  xmlns="http://maven.apache.org/POM/4.0.0"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

  <modelVersion>4.0.0</modelVersion>

  <parent>
    <groupId>com.soebes.smpp</groupId>
    <artifactId>smpp</artifactId>
    <version>4.0.1</version>
  </parent>

  <groupId>com.soebes.examples.j2ee</groupId>
  <artifactId>domain</artifactId>
  <version>${revision}</version>

...
</project>
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So now you can simply create release artifacts by using the following:

mvn -Drevision=1.2.3 clean package
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This will only create the artifacts in the target directory of your project. If you like to deploy them into a repository there are enhancements needed:

<project
  xmlns="http://maven.apache.org/POM/4.0.0"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

  <modelVersion>4.0.0</modelVersion>

  <parent>
    <groupId>com.soebes.smpp</groupId>
    <artifactId>smpp</artifactId>
    <version>4.0.1</version>
  </parent>

  <groupId>com.soebes.examples.j2ee</groupId>
  <artifactId>domain</artifactId>
  <version>${revision}</version>

  <build>
    <plugins>
      <plugin>
        <groupId>org.codehaus.mojo</groupId>
        <artifactId>flatten-maven-plugin</artifactId>
        <version>1.0.0</version>
        <configuration>
          <updatePomFile>true</updatePomFile>
        </configuration>
        <executions>
          <execution>
            <id>flatten</id>
            <phase>process-resources</phase>
            <goals>
              <goal>flatten</goal>
            </goals>
          </execution>
          <execution>
            <id>flatten.clean</id>
            <phase>clean</phase>
            <goals>
              <goal>clean</goal>
            </goals>
          </execution>
        </executions>
      </plugin>
    </plugins>
  </build>
</project>
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So from now on you can create a release by using the following command:

mvn -Drevision=1.2.3 clean deploy
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But of course a version can only be used once. So if you like to make another release you have to change the version but now it is really easy:

mvn -Drevision=1.2.4 clean deploy
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Currently there are three properties supported which can be used inside a version tag:

  1. revision
  2. sha1
  3. changelist

Only these three properties can be used inside a version tag. You can of course use combinations of them like this:

<version>${revision}${sha1}${changelist}</version>
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If you use different properties you will get a warning by Maven. I strongly encourage users to take notice of the warnings and of course clean them up.

So what about a multi module build? There you can use them as well. The parent will look like this:

<project
  xmlns="http://maven.apache.org/POM/4.0.0"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

  <modelVersion>4.0.0</modelVersion>

  <parent>
    <groupId>com.soebes.smpp</groupId>
    <artifactId>smpp</artifactId>
    <version>4.0.1</version>
  </parent>

  <groupId>com.soebes.examples.j2ee</groupId>
  <artifactId>parent</artifactId>
  <version>${revision}</version>
  <packaging>pom</packaging>
  ..
  [enhancements described earlier]
  ..
  <modules>
    <module>webgui</module>
    <module>app</module>
    <module>domain</module>
    <module>service</module>
    <module>service-client</module>
    <module>appasm</module>
    <module>assembly</module>
    <module>shade</module>
  </modules>
</project>
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and a child for example domain will look like this:

<project
  xmlns="http://maven.apache.org/POM/4.0.0"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

  <modelVersion>4.0.0</modelVersion>

  <parent>
    <groupId>com.soebes.examples.j2ee</groupId>
    <artifactId>parent</artifactId>
    <version>${revision}</version>
  </parent>


  <artifactId>domain</artifactId>
  ..
</project>
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You can now build the whole project from the root level by using the command:

mvn -Drevision=1.7.0-SNAPSHOT clean package
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The output will look like this:

[INFO] Scanning for projects...
[INFO] ------------------------------------------------------------------------
[INFO] Reactor Build Order:
[INFO]
[INFO] parent                                                             [pom]
[INFO] domain                                                             [jar]
[INFO] service-client                                                     [jar]
[INFO] webgui                                                             [war]
[INFO] service                                                            [ejb]
[INFO] app                                                                [ear]
[INFO] appasm                                                             [pom]
[INFO] shade                                                              [jar]
[INFO] assembly                                                           [pom]
[INFO]
[INFO] ------------------< com.soebes.examples.j2ee:parent >-------------------
[INFO] Building parent 1.7.0-SNAPSHOT                                     [1/9]
[INFO] --------------------------------[ pom ]---------------------------------
[INFO]
....
[INFO]
[INFO] -----------------< com.soebes.examples.j2ee:assembly >------------------
[INFO] Building assembly 1.7.0-SNAPSHOT                                   [9/9]
[INFO] --------------------------------[ pom ]---------------------------------
[INFO]
[INFO] --- maven-clean-plugin:3.1.0:clean (default-clean) @ assembly ---
[INFO] Deleting /Users/kama/ws-git/javaee/assembly/target
[INFO]
[INFO] --- flatten-maven-plugin:1.0.0:clean (flatten.clean) @ assembly ---
[INFO] Deleting /Users/kama/ws-git/javaee/assembly/.flattened-pom.xml
[INFO]
[INFO] --- jacoco-maven-plugin:0.8.1:prepare-agent (default) @ assembly ---
[INFO] argLine set to -javaagent:/Users/kama/.m2/repository/org/jacoco/org.jacoco.agent/0.8.1/org.jacoco.agent-0.8.1-runtime.jar=destfile=/Users/kama/ws-git/javaee/assembly/target/jacoco.exec
[INFO]
[INFO] --- flatten-maven-plugin:1.0.0:flatten (flatten) @ assembly ---
[INFO] Generating flattened POM of project com.soebes.examples.j2ee:assembly:pom:1.7.0-SNAPSHOT...
[INFO]
[INFO] --- maven-site-plugin:3.7.1:attach-descriptor (attach-descriptor) @ assembly ---
[INFO] No site descriptor found: nothing to attach.
[INFO]
[INFO] --- maven-assembly-plugin:3.0.0:single (assemblies) @ assembly ---
[INFO] Reading assembly descriptor: jar-with-prod.xml
[INFO] Reading assembly descriptor: assembly.xml
[INFO] Reading assembly descriptor: jar-with-dev.xml
[INFO] Building jar: /Users/kama/ws-git/javaee/assembly/target/assembly-1.7.0-SNAPSHOT-prod.jar
[INFO] Building zip: /Users/kama/ws-git/javaee/assembly/target/assembly-1.7.0-SNAPSHOT-archive.zip
[INFO] Building jar: /Users/kama/ws-git/javaee/assembly/target/assembly-1.7.0-SNAPSHOT-dev.jar
[INFO] ------------------------------------------------------------------------
[INFO] Reactor Summary:
[INFO]
[INFO] parent 1.7.0-SNAPSHOT .............................. SUCCESS [  1.535 s]
[INFO] domain ............................................. SUCCESS [  0.876 s]
[INFO] service-client ..................................... SUCCESS [  0.111 s]
[INFO] webgui ............................................. SUCCESS [  0.474 s]
[INFO] service ............................................ SUCCESS [  0.454 s]
[INFO] app ................................................ SUCCESS [  0.282 s]
[INFO] appasm ............................................. SUCCESS [  0.237 s]
[INFO] shade .............................................. SUCCESS [  0.443 s]
[INFO] assembly 1.7.0-SNAPSHOT ............................ SUCCESS [  1.238 s]
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 6.292 s
[INFO] Finished at: 2018-08-26T15:57:12+02:00
[INFO] ------------------------------------------------------------------------
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So it is now really easy to create a release from the whole project by using the following command:

mvn -Drevision=1.7.0 clean deploy
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This would result in a release deployed to a repository manager. So now let us take a look onto using it in a continuous integration solution like Jenkins. On Jenkins you have often the situation to produce artifacts on a branch base (maybe SNAPSHOT based to be able to deploy them to test environments). So you can combine the properties like this:

<project
  xmlns="http://maven.apache.org/POM/4.0.0"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

  <modelVersion>4.0.0</modelVersion>

  <parent>
    <groupId>com.soebes.smpp</groupId>
    <artifactId>smpp</artifactId>
    <version>4.0.1</version>
  </parent>

  <groupId>com.soebes.examples.j2ee</groupId>
  <artifactId>domain</artifactId>
  <version>${revision}${sha1}${changelist}</version>

  <properties>
    <revision>1.0.0</revision>
    <sha1/>
    <changelist/>
  </properties>
...
</project>
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In your jenkins pipeline you can extract the branch name and insert it into the build call like this:

mvn -Dsha1=-BRANCHNAME -Dchangelist=-SNAPSHOT clean deploy
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This approach has the advantage that on each branch you are using a different version which are distinguished by the -BRANCHNAME and those versions are snapshots. This is convenient cause, all repositoy managers have support to delete snapshot versions after some time automatically.

Top comments (7)

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kubo44 profile image
kubo44 •

Thank you for good hints, but they are little confusing. At the beginning it's recommended not to use SNAPSHOT versions but at the end, final example is with SNAPSHOT version, because it's good for deleting old versions automatically. What is the recommended way then to build snapshot and release versions? I guess snapshot with -Dchangelist=-SNAPSHOT and release without it (on demand to keep binaries), right?

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iplaman profile image
Idan Bidani •

Thanks, that will save the "mvn versions:set -DnewVersion=1.2.3"

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misterbaantjer profile image
Mister Baantjer •

Hi, nice article, but how do you determine the numbering automaticly?

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helpermethod profile image
Oliver Weiler • • Edited

CI systems like Jenkins normally create a Build Number on each Build, which is automatically incremented with each build. The Build Number is normally exposed a a environment variable.

mvn -Drevision=$BUILD_NUMBER clean deploy

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rootik profile image
Ihor Indyk •

This will not work for MyGet maven feeds. MyGet analyses pom.xml and gets confused by ${revision} in version field, giving you 400 on attempt to upload the package.

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kaus02 profile image
Kaustubh •

But how to record this change in version in scm?

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tomaszgaluszka profile image
Tomasz •

Nice article not only covering the basics of how to use these three magic variables, but also revealing the real use cases. Thanks a lot !

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