Maven does not replace a variable in 'settings.xml' when it is invoked

Question

I have defined a local mirror for all repositories in the settings.xml file:

<mirror>
  <id>myMirror</id>
  <mirrorOf>*</mirrorOf>
  <url>file://${mypath}/maven/.m2/repository</url>
</mirror>

I want that my mirror to point to a local path, in this case the path is:

file://${mypath}/maven/.m2/repository

Where ${mypath} is a variable that I pass when I invoke Maven:

 mvn -Dmypath="/D:/test" package

The problem is that Maven does not replace the variable when it is invoked. I can see that this error is happening by inspection of the build log. For example, Maven reports that it is downloading a file from file://${mypath}/maven/.m2/repository when the correct would be file:///D:/test/maven/.m2/repository.

I have also noted that Maven replaces correctly my variable when it is inserted in the url child tag of the repository tag:

<repository>
        <id>central</id>
        <url>http://${mypath}/maven/.m2/repository&lt;/url&gt;
</repository>

The build works correctly when I replace the variable in my settings.xml by the complete URL like in the example below:

<mirror>
        <id>myMirror</id>
        <mirrorOf>*</mirrorOf>
        <url>file:///D:test/maven/.m2/repository</url>
</mirror>

Answer 1

It is probably a bug - unfortunately property replacement does not seem to be consistent across Maven plugins. I have encountered a bug myself around specifying more than two properties in a configuration item in another plugin.

Answer 2

The settings.xml is not interpolated like the pom is, so the property can't be used like shown above.

Answer 3

Property substitution into settings.xml doesn't work as you would expect.

It will substitute properties inside the profiles element (as you've seen it substitutes into your repository url, which would be defined inside a profile), but not to elements outside of profiles (as you've seen happening in the mirrors section). This distinction is made because the profile element in the settings.xml is a truncated version of the pom.xml profile element. It is a mechanism to allow configuration to be set into your POM, so property substitution is allowed within the profiles elements as they are effectively part of the POM.

The parts of the settings outside of the profiles element represent the platform configuration, these aren't supposed to be affected by individual builds, so are not substituted for command-line properties. This makes sense but isn't really made clear anywhere.

---

There is a workaround though, you can substitute environment variables into the settings.xml. If you set the environment variable:

set M2_MIRROR=D:\test

and configure the repository url as follows:

<url>file://${M2_MIRROR}/maven/.m2/repository</url>

Then invoke Maven as normal, the environment variable is substituted and your build should work as required.