Differences between dependencyManagement and dependencies in Maven

Question

What is the difference between dependencyManagement and dependencies? I have seen the docs at Apache Maven web site. It seems that a dependency defined under the dependencyManagement can be used in its child modules without specifying the version.

For example:

A parent project (Pro-par) defines a dependency under the dependencyManagement:

<dependencyManagement>   <dependencies>     <dependency>       <groupId>junit</groupId>       <artifactId>junit</artifactId>       <version>3.8</version>     </dependency>  </dependencies> </dependencyManagement> 

Then in the child of Pro-par, I can use the junit:

  <dependencies>     <dependency>       <groupId>junit</groupId>       <artifactId>junit</artifactId>     </dependency>  </dependencies> 

However, I wonder if it is necessary to define junit in the parent pom? Why not define it directly in the needed module?

Answer 1

I'm fashionably late to this question, but I think it's worth a clearer response than the accepted one (which is correct, but doesn't emphasize the actual important part, which you need to deduce yourself).

In the parent POM, the main difference between the <dependencies> and <dependencyManagement> is this:

• Artifacts specified in the <dependencies> section will ALWAYS be included as a dependency of the child module(s).

• Artifacts specified in the <dependencyManagement> section, will only be included in the child module if they were also specified in the <dependencies> section of the child module itself. Why is it good you ask? Because you specify the version and/or scope in the parent, and you can leave them out when specifying the dependencies in the child POM. This can help you use unified versions for dependencies for child modules, without specifying the version in each child module.

Answer 2

Dependency Management allows to consolidate and centralize the management of dependency versions without adding dependencies which are inherited by all children. This is especially useful when you have a set of projects (i.e. more than one) that inherits a common parent.

Another extremely important use case of dependencyManagement is the control of versions of artifacts used in transitive dependencies. This is hard to explain without an example. Luckily, this is illustrated in the documentation.