Maven settings

Maven settings

You can use a global settings file to avoid littering the pom.xml files with non-project-related settings, such as the location on you local disk for the repository cache, and settings for proxies and remote servers.

To set this up, create an file in the .m2 folder named settings.xml. An empty version of this might look like this:

<settings xmlns="http://maven.apache.org/SETTINGS/1.0.0" 
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
    xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0
                        https://maven.apache.org/xsd/settings-1.0.0.xsd"> 
    <localRepository/>
    <interactiveMode/>
    <usePluginRegistry/>
    <offline/>
    <pluginGroups/> 
    <servers/>
    <mirrors/>
    <proxies/>
    <profiles/> 
    <activeProfiles/> 
</settings> 

To customise the behaviour of your machine without affecting others, add entries into the settings.xml file.

Store the cache elsewhere

I don’t like having the ‘repository’ folder in the .m2 folder because it clutters it. Also I have the .m2 folder under version control because I value the effort made in creating the settings.xml file. Another reason to move it is to host it on another volume, either for performance reasons or to save disk space on higher-performing devices.

<localRepository>/data/.m2/repository</localRepository> 

This entry moves the file store for Maven. Make sure it has read/write access and enough disk space.

Nexus mirrors

Using a Nexus mirror is a great idea because it solves a number of key problems with Maven:

• it saves you bandwidth by reducing the number of downloads onto your network

• it accelerates build time by placing dependencies closer

• it gives you certainty that a dependency will be available making the build more robust

• it hosts the output of your builds, so they can become immutable

• it can proxy other repositories, simplifying development configuration

To set this in the settings.xml, add this fragment to configure the mirrors used by Maven.

  <mirrors>
    <mirror>                               
      <id>nexus</id>        
      <mirrorOf>*</mirrorOf>        
      <url>http://<host>/content/groups/public</url>                         
    </mirror>  
  </mirrors> 

This declares that everything has been mirrored by your Nexus server. If you need to add a new external repository, all you need to do is add it to Nexus as a proxy service without the need to change anything else.

Selecting from multiple settings.xml files

It’s trivial to use a different set of settings at build time. This can be very useful, such as when switching between projects or clients, or when you aren’t on your home network but can’t run the build in offline mode because there are new public dependencies.

mvn -s ~/.m2/another-settings-file.xml install

This will use the alternative settings that you’ve created instead of the normal settings.xml file. I like to use this for a ‘no settings’ version that has everything as default for when the Nexus server is unavailable but I need to build a new project.

Project specific settings file

Some projects will have a settings file in the SCM repository for safekeeping and sharing, and if you work on multiple projects with different settings it might be best to invoke Maven like this:

mvn -s settings.xml install

This will use the settings.xml file in the current directory.