dependencyManagement BOM question

[David Hoffer <dh...@gmail.com>]

I have some questions regarding how importing a pom type dependency in my
dependencyManagement section really works (e.g. BOM dependency).  At a
basic level I understand it will effectively add all its dependencies
defined in its dependencyManagement section to my dependencyManagement
section.

However the imported pom uses variables for all the versions and defines
them in its pom.  Now if I want to use a different version and also have
the version variable (same variable name) set in my pom, which version will
be used?

What about order of the BOM import?  Does the order of the BOM import
matter with respect to other non imported dependencyManagement
dependencies?  If my POM has the same dependency of the imported one which
one will be used?  Lets say in one case I'm using a property variable to
specify the version and also if I use a literal version.

-Dave

Re: dependencyManagement BOM question

[Christian Schulte <cs...@schulte.it>]

Am 08/23/16 um 21:27 schrieb David Hoffer:
> I have some questions regarding how importing a pom type dependency in my
> dependencyManagement section really works (e.g. BOM dependency).  At a
> basic level I understand it will effectively add all its dependencies
> defined in its dependencyManagement section to my dependencyManagement
> section.

Not all. Only the dependencies not already declared in your effective
dependency management. Implemented in class
'org.apache.maven.model.composition.DefaultDependencyManagementImporter'

<https://git-wip-us.apache.org/repos/asf?p=maven.git;a=blob;f=maven-model-builder/src/main/java/org/apache/maven/model/composition/DefaultDependencyManagementImporter.java;h=c3a0201b34be6402333f90ed4b807ec62e9ff898;hb=HEAD>

based on method 'getManagementKey' of class
'org.apache.maven.model.Dependency'

<https://git-wip-us.apache.org/repos/asf?p=maven.git;a=blob;f=maven-model/src/main/mdo/maven.mdo;h=8abf29ed89d256e5dbf889f7e813c1d5bf79844e;hb=629fd749e59a679809c86eb26d554520e4de3a78#l1456>.

> 
> However the imported pom uses variables for all the versions and defines
> them in its pom.  Now if I want to use a different version and also have
> the version variable (same variable name) set in my pom, which version will
> be used?

Maven imports the effective dependency management of the BOM (after
inheritance, interpolation, etc.). Consider the BOM a standalone project
without any relationship to the importing POM.

> 
> What about order of the BOM import?  Does the order of the BOM import
> matter with respect to other non imported dependencyManagement
> dependencies?  If my POM has the same dependency of the imported one which
> one will be used?  Lets say in one case I'm using a property variable to
> specify the version and also if I use a literal version.
> 

Effective dependencies of the POM override what gets imported. See
above. When using multiple BOM imports in the POM, the order of
declaration of those imports matter (after inheritance, interpolation,
etc.). As of Maven 3.4.0-SNAPSHOT you'll get a warning when your POM
depends on this "first declaration wins" itch. Relying on the order of
XML elements should be avoided.

Regards,
-- 
Christian


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