Continuous Delivery with Maven and Jenkins

Motivation: Every jenkins build produces a potential release and as such each build should have a unique version number. This post shows how to use the Jenkins build number to archive this.

The basic idea is to use a variable as part of the <version>…</version> declaration in your pom.xml. This variable is set to 1.0-SNAPSHOT by default for local builds and when executed on jenkins to ‘1.0-<BUILD_NUMBER>’.

<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/maven-v4_0_0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>de.torstenwalter.examples</groupId>
    <artifactId>jenkins-versioning</artifactId>
    <version>${revision}</version>

    <properties>
        <baseRevision>1.0</baseRevision>
        <revision>${baseRevision}-SNAPSHOT</revision>
    </properties>

    <profiles>
        <profile>
            <id>jenkins</id>
            <activation>
                <property>
                    <name>env.BUILD_NUMBER</name>
                </property>
            </activation>
            <properties>
                <revision>${baseRevision}-${env.BUILD_NUMBER}</revision>
            </properties>
        </profile>
    </profiles>
</project>

As variable name for the version ${revision} is used as it is explicitly allowed since maven 3.2.1 at that location (see improvement MNG-5576).

This is the warning if you try to use a different variable name e.g. ${myVar} instead of ${revision}:

[WARNING] Some problems were encountered while building the effective model for de.torstenwalter.examples:jenkins-versioning:jar:${myVar}
[WARNING] 'version' contains an expression but should be a constant. @ line 7, column 14
[WARNING]
[WARNING] It is highly recommended to fix these problems because they threaten the stability of your build.
[WARNING]
[WARNING] For this reason, future Maven versions might no longer support building such malformed projects.
[WARNING]

This snippet sets the default value for revision to 1.0-SNAPSHOT:

    <properties>
        <baseRevision>1.0</baseRevision>
        <revision>${baseRevision}-SNAPSHOT</revision>
    </properties>

baseRevision is meant to provide the base version e.g. 1.0 or 2.3 where the build number is later appended or -LATEST for local builds.

The build number is included as part of the version by using a maven profile which is automatically enabled when the environment variable BUILD_NUMBER is present.

        <profile>
            <id>jenkins</id>
            <activation>
                <property>
                    <name>env.BUILD_NUMBER</name>
                </property>
            </activation>
            <properties>
                <revision>${baseRevision}-${env.BUILD_NUMBER}</revision>
            </properties>
        </profile>

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