10 Maven Multi-Module Best Practices
Maven is a powerful tool that can help you manage projects with multiple modules. Here are 10 best practices to follow.
Maven is a popular build automation tool used by many Java developers. It is used to manage the build process, dependencies, and other aspects of the software development lifecycle. One of the most powerful features of Maven is its ability to create multi-module projects. This allows developers to break down their projects into smaller, more manageable modules.
In this article, we will discuss 10 best practices for creating and managing multi-module projects with Maven. We will cover topics such as project structure, dependency management, and more. By following these best practices, you can ensure that your Maven projects are well-structured and maintainable.
1. Keep the parent POM in a separate repository
The parent POM is the root of your project, and it contains all the configuration information for each module. If you keep this in a separate repository, then any changes to the parent POM will be immediately visible to all modules. This makes it easier to manage and maintain the project as a whole.
It also allows developers to work on different modules independently without having to worry about conflicting changes to the parent POM. Keeping the parent POM in a separate repository ensures that everyone has access to the same version of the parent POM, which helps reduce errors and confusion.
2. Use Maven versions plugin to manage versions
The Maven versions plugin allows you to easily update the version of a module or all modules in your project. This is especially useful when you need to make changes across multiple modules, such as updating dependencies or changing the parent POM. Without the Maven versions plugin, this process can be tedious and time-consuming.
Using the Maven versions plugin also helps ensure that all modules have the same version number, which makes it easier to track changes and identify any potential issues. Additionally, using the Maven versions plugin ensures that all modules are up-to-date with the latest version numbers, making it easier for other developers to work on the project.
3. Don’t use dependencies with scope import
When you use a dependency with scope import, it means that the transitive dependencies of this imported module will be available to all other modules in your multi-module project. This can lead to unexpected behavior and conflicts between different versions of the same library.
It’s better to explicitly declare each dependency in each module so that you have full control over which version is used. This also makes it easier to debug any issues related to conflicting libraries.
4. Avoid using relativePath for parent declaration
When using relativePath, the parent POM is resolved from the local filesystem. This means that if you have multiple developers working on the same project, they will all need to have the exact same directory structure in order for the build to work properly. This can be difficult to maintain and can lead to errors when someone makes a change to the directory structure without updating the relativePath declaration.
Instead of using relativePath, it’s better to use an absolute path or a URL pointing to a repository where the parent POM is stored. This way, everyone has access to the same version of the parent POM regardless of their local environment.
5. Avoid using version ranges
When you use version ranges, Maven will try to resolve the dependency at build time. This means that if a new version of the dependency is released, it may be resolved and used in your project without you knowing about it. This can lead to unexpected behavior or even errors due to incompatibilities between versions.
To avoid this problem, always specify exact versions for all dependencies. This way, you know exactly which version of the dependency will be used in your project, and you won’t have any surprises when building or running your application.
6. Always define explicit dependency versions
When you define explicit versions for your dependencies, Maven will always use the same version of a dependency across all modules. This ensures that all modules are using the same version of the dependency and prevents any potential conflicts or issues due to different versions being used in different modules.
It also makes it easier to manage and update dependencies since you only need to change the version number in one place instead of having to search through multiple modules. Finally, it helps ensure that all modules have consistent behavior since they’re all using the same version of the dependency.
7. Define default Java compiler level
When you define the default Java compiler level, it ensures that all modules in your project are compiled with the same version of Java. This helps to avoid any potential compatibility issues between different versions of Java and makes sure that all modules can be built successfully.
To set the default Java compiler level, add the following configuration to your parent POM file:
8. Set up checkstyle, findbugs and PMD plugins
These plugins help to ensure that the code is written in a consistent style, and that it adheres to certain coding standards. This makes it easier for developers to read and understand each other’s code, which can save time and effort when debugging or making changes. Additionally, these plugins can detect potential bugs before they become an issue, saving even more time and money. Finally, setting up these plugins helps to promote good coding practices, which can lead to better overall software quality.
9. Run integration tests in a separate module
Integration tests are designed to test the interaction between different components of a system. When running integration tests in the same module as unit tests, it can lead to false positives and negatives due to the dependencies between the two types of tests. By separating them into separate modules, you can ensure that each type of test is run independently and accurately.
Additionally, by having a dedicated module for integration tests, you can easily configure Maven to only run those tests when necessary. This helps reduce build times and makes sure that your builds are more reliable.
10. Use profiles to build different artifacts
Profiles allow you to define different sets of configuration and build settings for each module. This means that you can create a profile for each type of artifact you want to build, such as a web application or an executable jar file. By using profiles, you can easily switch between building different artifacts without having to manually change the configuration in each module.
Using profiles also makes it easier to maintain your multi-module project since all of the configurations are stored in one place. This reduces the risk of errors due to manual changes being made in multiple modules.