Using Maven

Author: Tayeb Merabti
Small modifications: Paweł Guzewicz

1. Maven versioning:
   In Maven, when you deploy a new version of your JAR file, this version will be downloaded only once to the local repository because Maven never re-downloads releases. For this reason, new releases should use a new version number. In other words, when you are using 1.0, once Maven has downloaded this artifact as a release, it never tries to get a new 1.0 from the remote repository.If the project is still under development, you should use the -SNAPSHOT version. In this case, Maven will check for updates, and download or re-download the latest version from the remote repository to the local since the snapshots modules are stored with a timestamp and a build number and can be easily tracked.
2. Using SNAPSHOT versions:
   1. In pom.xml, under <version> tag change the name to version-SNAPSHOT (e.g. 0.0.1-SNAPSHOT).
   2. Before running mvn deploy, it is important to configure correctly the snapshot server in the project pom.xml and in the settings.xml file:
      1. In the pom.xml, before the closing </build> tag add the <distibutionManagement>…</distibutionManagement> element:
         [
         <build>
         …
         …
         …
         <distributionManagement>
         <repository>
         <id>cedarcommons-private-release</id>
         <name>CEDAR-commons MVN release repo</name><url>http://maven.inria.fr/artifactory/cedarcommons-private-release</url></repository>
         <snapshotRepository>
         <id>cedarcommons-private-snapshot</id>
         <name>CEDAR-commons MVN snapshot repo</name>
         <url>http://maven.inria.fr/artifactory/cedarcommons-private-snapshot</url>
         </snapshotRepository>
         </distributionManagement>
         </build>
         ]
         where cedarcommons-private-release corresponds to the release repository and cedarcommons-private-snapshot to the snapshot repository.
      2. The settings.xml file under the ~/.m2 directory must contain all connection information to release and snapshot repositories.Under the <servers> element add this server, note the password for the snapshot repository is the same password for the release repository:
         <server>
         <id>cedarcommons-private-snapshot</id>
         <username>cedar-private-writer</username>
         <password>****</password>
         </server>Under the <repositories> element add:
         <repository>
         <id>cedarcommons-private-snapshot</id>
         <name>CEDAR commons MVN snapshot repo</name>
         <url>http://maven.inria.fr/artifactory/cedarcommons-private-snapshot</url>
         <layout>default</layout>
         <releases>
         <enabled>false</enabled>
         </releases>
         <snapshots>
         <enabled>true</enabled>
         </snapshots>
         </repository>
3. Deployment
   Run mvn deploy to deploy the new snapshot version in the snapshot repository.
4. Update:
   Run mvn clean install to update dependencies in the local repository with the latest snapshot version.
5. Best practices (to be extended…):
   Before the deployment of any packages, be sure that the latest dependencies “release and/or snapshot” are in remote repositories.Example: Suppose that you have two maven projects: A and B. Project B is one of the dependencies of project A. Locally, you make some changes in project B and you need to deploy project A. Before the deployment of A in the remote repository you need to deploy the updated version of B first.
6. Advanced tips (not finished) and how to use mvn release:prepare and mvn release:perform:
   It is possible to link a maven project with a GitLab repository. To do so, in the pom.xml file, you need to add:
   <scm>
   <url>https://gitlab.inria.fr/cedar/gitProjectName.git</url>
   <connection>scm:git:git@gitlab.inria.fr:cedar/gitProjectName.git</connection>
   <developerConnection>scm:git:git@gitlab.inria.fr:cedar/gitProjectName.git</developerConnection>
   </scm>

   Then, after the scm element, add the maven-release-plugin:
   <plugins>
   <plugin>
   <groupId>org.apache.maven.plugins</groupId>
   <artifactId>maven-release-plugin</artifactId>
   <version>2.5.3</version>
   <configuration>
   <tagNameFormat>@{project.version}</tagNameFormat>
   <autoVersionSubmodules>true</autoVersionSubmodules>
   <releaseProfiles>releases</releaseProfiles>
   </configuration>
   </plugin>
   </plugins>
   Now, the project is configured with your GitLab repository and any change will be mentioned. For this, you can run mvn release:prepare.

7. Useful commands:
   1. mvn dependency:analyze
      Finds explicit and implicit dependencies in the project and suggests to add or remove dependencies in pom.xml
   2. mvn versions:display-dependency-updates
      Shows the newest versions of your dependencies in pom.xml
   3. mvn versions:display-plugin-updates
      Shows the newest versions of plugins in pom.xml