Maven: Create a simple build number

It’s always a good idea to have means to integrate a build number within your application. It makes it easy to find out which exact versions are deployed on your stages our what version you’re users are running in case of third level support.

The task of creating unique build numbers can easily be automated using maven.

A build number can contain all kind of information, like the application version, a sequential number, SCM revision or a time stamp.

From my point of view, using the time stamp when creating a unique build number is essential: It is unique per se (it is unlikely that the same system is build twice in one second) and it is generated by maven without depending on any plugins. In addition, it is easy to understand, like “Did operations really deploy the new version of the application, yet? No, the build number still shows that it’s the one from last week!”.

So let’s get to buisness: How to generate build numbers within a JAR and how to read it? Does it also work with WARs?

JAR

As mentioned before, maven provides a built-in mechanism for creating a timestamp. You can just customize the formatting and use it for your build number within your pom.xml like so:

	<properties>
		<maven.build.timestamp.format>yyyyMMddHHmmss</maven.build.timestamp.format>
		<buildNumber>v.${project.version} build ${maven.build.timestamp}</buildNumber>
	</properties>

Please note that using the property maven.build.timestamp directly within your filtered file is not possible due to this bug.

The build number must no be made accessible to your application. There are at least two solutions at hand: Write the build number to your manifest or create a properties file.

Manifest

pom.xml

	<build>
		<!-- Add build number to manifest -->
		<plugins>
			<plugin>
				<groupId>org.apache.maven.plugins</groupId>
				<artifactId>maven-jar-plugin</artifactId>
				<configuration>
					<archive>
						<manifestEntries>
							<build>${buildNumber}</build>
						</manifestEntries>
						<manifest>
							<mainClass>info.schnatterer.Main</mainClass>
						</manifest>
					</archive>
				</configuration>
			</plugin>
		</plugins>
	</build>

And that’s how you can access it from your application:

	private String getBuildNumberFromManifest() throws IOException {
		InputStream manifestStream = getClass().getClassLoader()
				.getResourceAsStream("META-INF/MANIFEST.MF");
		if (manifestStream != null) {
			Manifest manifest = new Manifest(manifestStream);
			Attributes attributes = manifest.getMainAttributes();
			return attributes.getValue("build");
		}
		return null;
	}

Properties

Alternatively, create use a properties file:

build.properties

buildNumber=${buildNumber}

pom.xml

	<build>
		<resources>
			<resource>
				<!-- Filter for build number -->
				<directory>src/main/resources</directory>
				<filtering>true</filtering>
				<includes>
					<include>build.properties</include>
				</includes>
			</resource>
		</resources>
	</build>

And that’s how you can access it from your application:

	private String getBuildNumberFromProps() throws IOException {
		String propertiesName = "/build.properties";

		InputStream propertiesStream = Main.class
				.getResourceAsStream(propertiesName);
		if (propertiesStream != null) {
			Properties pros = new Properties();
			pros.load(propertiesStream);

			return pros.getProperty("buildNumber");
		}
		return null;
	}

The output looks something like this:

v.0.0.1-SNAPSHOT build 20140225211328

Note: You might want to check the returned value for null or have the methods return empty Strings in order to avoid NullPointerExceptions or the word null on your GUI.

WAR

If you’re building a web application, you should also be able to use the manifest or the properties file as described above. Your maven set up might be a bit different, though (see Maven War plugin – WAR Manifest Customization).

You have another alternative that makes creating the build number even easier: You can “stamp” the build number directly into interpreted documents like (X)HTML or js files.

For example when using JSF, you could write the build number directly into the footer template.

Add this to your page:

<h:outputText styleClass="version" value="${buildNumber}"/>

And this to your pom.xml

	<properties>
		<maven.build.timestamp.format>yyyy-MM-dd HH:mm:ss</maven.build.timestamp.format>
		<buildNumber>v.${project.version} build ${maven.build.timestamp}</buildNumber>
	</properties>

	<build>
		<plugins>
			<plugin>
				<groupId>org.apache.maven.plugins</groupId>
				<artifactId>maven-war-plugin</artifactId>
				<version>2.3</version>
				<configuration>
					<!-- Filter for build number -->
					<webResources>
						<resource>
							<directory>src/main/webapp/WEB-INF/templates</directory>
							<targetPath>WEB-INF/templates</targetPath>
							<filtering>true</filtering>
							<includes>
								<include>yourFooterTemplate.xhtml</include>
							</includes>
						</resource>
					</webResources>
				</configuration>
			</plugin>
		</plugins>
	</build>

And that’s it. No parsing necessary in code, as maven will insert the build number in your web page directly.

Further Reading

If you’re planning on creating a more complex build number (SCM, sequential numbers, etc.), I suggest you have a look at the Build Number Maven Plugin.

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