Access Maven informations in code

Introduction#

It is sometimes useful to get the maven properties, such as the current version, in code. Here are some ways to to it.

Getting the version number from within a jar

If you package your application in a jar using the maven-jar-plugin or the maven-assembly-plugin, an easy way to get the current pom version is to add an entry in the manifest, which is then available from Java.

The secret is to set the addDefaultImplementationEntries flag to true (and the addDefaultSpecificationEntries is you also need the artifact id).

jar plugin configuration:

<build>
  <plugins>
    <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-jar-plugin</artifactId>
      <configuration>
        <archive>
          <manifest>
            <mainClass>...</mainClass>
            <addDefaultImplementationEntries>
              true
            </addDefaultImplementationEntries>
          </manifest>
        </archive>
      </configuration>
    </plugin>
  </plugins>
</build>

assembly plugin configuration:

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-assembly-plugin</artifactId>
    <configuration>
        <descriptorRefs>
            <descriptorRef>jar-with-dependencies</descriptorRef>
        </descriptorRefs>
        <archive>
            <manifest>  
              <addDefaultImplementationEntries>true</addDefaultImplementationEntries> 
            </manifest>
        </archive>
    </configuration>
    <executions>
        <execution .../>
    </executions>
</plugin>

addDefaultImplementationEntries instructs Maven to add the following headers to the MANIFEST.MF of your jar:

Implementation-Title: display-version
Implementation-Version: 1.0-SNAPSHOT
Implementation-Vendor-Id: test

Now you can use this line of code anywhere in your jar to access the version number:

getClass().getPackage().getImplementationVersion()

More information here and here.

Keeping a properties file in sync using maven’s property filtering mecanism

As this documentation explains,

Sometimes a resource file will need to contain a value that can only be supplied at build time. To accomplish this in Maven, put a reference to the property that will contain the value into your resource file using the syntax ${<property name>}. The property can be one of the values defined in your pom.xml, a value defined in the user’s settings.xml, a property defined in an external properties file, or a system property.

As an example, let’s create a simple info.txt in src/main/resources containing the pom version and the build time.

create a src/main/resources/info.txt with the following content:

version=${pom.version} build.date=${timestamp}

ask Maven to expand the properties by setting filtering to true:

 <build>
     <resources>
         <resource>
            <directory>src/main/resources</directory>
            <filtering>true</filtering>
         </resource>
     </resources>
 </build>

with that, the version will be updated, but unfortunately a bug within Maven prevents the ${maven.build.timestamp} property from getting passed to the resource filtering mechanism (more info here). So, let’s create a timestamp property as a workaround ! Add the following to the pom’s properties:
```
 <properties>
     <timestamp>${maven.build.timestamp}</timestamp>
     <maven.build.timestamp.format>yyyy-MM-dd'T'HH:mm</maven.build.timestamp.format>  
 </properties>
```
run maven, you should find a info.txt in target/classes with a content like:
```
 version=0.3.2
 build.date=2017-04-20T13:56
```

Reading a pom.xml at runtime using maven-model plugin

The other examples may be the best and most stable way to get a version number into an application statically. This answer proposes an alternative showing how to do it dynamically during runtime, using the maven maven-model library.

Add the dependency:

<dependency>
  <groupId>org.apache.maven</groupId>
  <artifactId>maven-model</artifactId>
  <version>3.3.9</version>
</dependency>

In Java, create a MavenXpp3Reader to read your pom. For example:

package de.scrum_master.app;

import org.apache.maven.model.Model;
import org.apache.maven.model.io.xpp3.MavenXpp3Reader;
import org.codehaus.plexus.util.xml.pull.XmlPullParserException;

import java.io.FileReader;
import java.io.IOException;

public class MavenModelExample {
    public static void main(String[] args) throws IOException, XmlPullParserException {
        MavenXpp3Reader reader = new MavenXpp3Reader();
        Model model = reader.read(new FileReader("pom.xml"));
        System.out.println(model.getId());
        System.out.println(model.getGroupId());
        System.out.println(model.getArtifactId());
        System.out.println(model.getVersion());
    }
}

The console log is as follows:

de.scrum-master.stackoverflow:my-artifact:jar:1.0-SNAPSHOT
de.scrum-master.stackoverflow
my-artifact
1.0-SNAPSHOT