Maven build all in order

Question

I have a project where all of my projects have a parent pom defined like this:

<parent>
    <groupId>MyProject</groupId>
    <artifactId>MyApp</artifactId>
    <version>1.0</version>
</parent>

However, this parent pom does NOT specify the modules in a modules element.

So when I run the mvn install -f parent/pom.xml command it doesn't do anything.

Is there some OTHER way I can build the entire project In Order so that all of the poms are built?

By "in order" i mean "built in order of dependency". Because several projects depend on others, we can't just build each project alphabetically.

Answer 1

If you have a reactor pom (a pom with the <modules> element, and <packaging> defined as pom) then the modules will be built in dependency order. This ordering happens regardless of the order the modules are specified in the pom.

There's a few ways to approach this:

Option 1

Your reactor pom doesn't need to be the same pom as your parent pom. So you could have:

project/pom.xml          # Reactor pom with <modules> element
project/parent/pom.xml   # Parent pom
project/module-a/pom.xml # Some module 'a'
project/module-b/pom.xml # Some module 'b'

In this case, the reactor pom contains:

<modules>
  <module>parent</module>
  <module>module-a</module>
  <module>module-b</module>
</modules>

Running mvn install at the top level will build your parent pom, and the two modules in dependency order.

Option 2

Move your parent pom up a directory, and use it as both a parent pom and a reactor pom, so your project looks like this

project/pom.xml          # Parent/Reactor pom with <modules> element
project/module-a/pom.xml # Some module 'a'
project/module-b/pom.xml # Some module 'b'

The modules section in it would look like this

<modules>
  <module>module-a</module>
  <module>module-b</module>
</modules>

Again, running mvn install at the top level will build your parent pom, and the two modules in dependency order.

Option 3

Leave your parent pom where it is, and add a modules section:

<modules>
  <module>../module-a</module>
  <module>../module-b</module>
</modules>

In this case, running mvn install -f parent/pom.xml will build the parent pom, and the two modules in dependency order.

Conclusion

I normally use Option 2. It's the pattern that's most used in maven itself, and I try to avoid straying too far from the 'beaten path', which is widely understood and tested.

For more information, see the Guide to Working with Multiple Modules.

Answer 2

There is no other way to resolve dependency between projects automatic during build.

What you can to resolve the dependency is to specify the order in which the build need to be done. Create a modules section on your parent POM to do so.

    <modules>
      <module>Proj A to Build/module>
      <module>Proj B dependent or Proj A</module>
    </modules>