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Do you use use Maven as the dependency manager for your projects? If so, this article will give you some insight into how it works, along with some useful commands. You will find these especially helpful if you are using a private repository as the main repo to source the dependencies for your project. By using the dependency list generation methods described in this article, you can greatly reduce the workload needed to make dependencies available in your private repository, or locally if you intend to run your project offline.

How Does Maven Manage Dependencies?

You add dependencies for your project to your Maven configuration file (also known as the  pom.xml file, for Project Object Model). As you build your project using Maven, it resolves these dependencies and downloads the dependencies to your local repository folder. This folder is usually located in your user’s home folder and is named .m2Each dependency downloaded from the repository is a project itself, and has its own dependencies. Maven recursively resolves all of these dependencies for you, and then merges shared dependencies and downloads them.  At the end of the process you end up with a list of dependencies that are needed to run your project on your local machine. For full details about how this process works, check out the Maven documentation.

How Do I Get the Dependencies for a Project?

From this brief description of how Maven dependencies work, you may notice a problem: How do you know exactly what dependencies are required for a project, and if you don’t have Internet access or are trying to run your project offline, how do you make sure you have all the dependencies you need available locally? Fortunately, Maven includes several commands that you can use to make sure you have all the dependencies and repositories set up so that your project will build and run with no errors.

  1. First, check for version updates to your dependencies, and then update the outdated dependencies in your pom.xml file as necessary.
    mvn versions:display-dependency-updates

  2. Get a list of your repositories, and make sure they’re pointing to all the correct dependencies.
    mvn dependency:list-repositories

  3. Get a list of your plugin and project dependencies, and make sure they’re all available in your private or local repository. 
    mvn dependency:go-offline

If you want to automate the process, or just get a cleaner output of your dependencies, you can also use this bash command:

mvn -o dependency:go-offline|grep ":*.jar"|awk '{split($0,a,":");print a[2]}'

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