The settings.xml File in Maven

1. Overview

While using Maven, we keep most of the project specific configuration in the pom.xml.

Maven provides a settings file – settings.xml. This allows us to specify which local and remote repositories it will use. We can also use it store settings that we don't want in our source code, such as credentials.

In this tutorial, we'll look at how to use the settings.xml. We'll look at proxies, mirroring, and profiles. We'll also look at how to determine the current settings that apply to our project.

2. Configurations

The settings.xml file configures a Maven installation. It's similar to a pom.xml file but is defined globally or per user.

Let's explore the elements we can configure in the settings.xml file. The main, settings element of the settings.xml file, can contain nine possible predefined child elements:

<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/>
    <offline/>
    <pluginGroups/>
    <servers/>
    <mirrors/>
    <proxies/>
    <profiles/>
    <activeProfiles/>
</settings>

2.1. Simple Values

Some of the top-level configuration elements contain simple values:

<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>${user.home}/.m2/repository</localRepository>
    <interactiveMode>true</interactiveMode>
    <offline>false</offline>
</settings>

The localRepository element points to the path of the system’s local repository. The local repository is where all the dependencies from our projects get cached. The default is to use the user's home directory. However, we could change it to allow all logged-in users to build from a common local repository.

The interactiveMode flag defines if we allow Maven to interact with the user asking for input. This flag defaults to true.

The offline flag determines if the build system may operate in offline mode. This defaults to false. However, we can switch it to true in cases where the build servers cannot connect to a remote repository.

2.2. Plugin Groups

The pluginGroups element contains a list of child elements that specify a groupId. A groupId is the unique identifier of the organization that created a specific Maven artifact:

<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">
    <pluginGroups>
        <pluginGroup>org.apache.tomcat.maven</pluginGroup>
    </pluginGroups>
</settings>

Maven searches the list of plugin groups when a plugin is used without a groupId provided at the command line. The list contains the groups org.apache.maven.plugins and org.codehaus.mojo by default.

The settings.xml file defined above allows us to execute truncated Tomcat plugin commands:

mvn tomcat7:help
mvn tomcat7:deploy
mvn tomcat7:run

2.3. Proxies

We can configure a proxy for some or all of Maven's HTTP requests. The proxies element allows a list of child proxy elements, but only one proxy can be active at a time:

<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">
    <proxies>
        <proxy>
            <id>baeldung-proxy</id>
            <active>true</active>
            <protocol>http</protocol>
            <host>baeldung.proxy.com</host>
            <port>8080</port>
            <username>demo-user</username>
            <password>dummy-password</password>
            <nonProxyHosts>*.baeldung.com|*.apache.org</nonProxyHosts>
        </proxy>
    </proxies>
</settings>

We define the currently active proxy via the active flag. Then, with the nonProxyHosts element, we specify which hosts are not proxied. The delimiter used depends on the specific proxy server. The most common delimiters are pipe and comma.

2.4. Mirrors

Repositories can be declared inside a project pom.xml. This means that the developers sharing the project code get the right repository settings out of the box.

We can use mirrors in cases when we want to define an alternative mirror for a particular repository. This overrides what's in the pom.xml.

For example, we can force Maven to use a single repository by mirroring all repository requests:

<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">
    <mirrors>
        <mirror>
            <id>internal-baeldung-repository</id>
            <name>Baeldung Internal Repo</name>
            <url>https://baeldung.com/repo/maven2/</url>
            <mirrorOf>*</mirrorOf>
        </mirror>
    </mirrors>
</settings>

We may define only one mirror for a given repository and Maven will pick the first match. Normally, we should use the official repository distributed worldwide via CDN.

2.5. Servers

Defining repositories in the project pom.xml is a good practice. However, we shouldn't put security settings, such as credentials, into our source code repository with the pom.xml. Instead, we define this secure information in the settings.xml file:

<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">
    <servers>
        <server>
            <id>internal-baeldung-repository</id>
            <username>demo-user</username>
            <password>dummy-password</password>
            <privateKey>${user.home}/.ssh/bael_key</privateKey>
            <passphrase>dummy-passphrase</passphrase>
            <filePermissions>664</filePermissions>
            <directoryPermissions>775</directoryPermissions>
            <configuration></configuration>
        </server>
    </servers>
</settings>

We should note that the ID of the server in the settings.xml needs to match the ID element of the repository mentioned in the pom.xml. The XML also allows us to use placeholders to pick up credentials from environment variables.

3. Profiles

The profiles element enables us to create multiple profile child elements differentiated by their ID child element. The profile element in the settings.xml is a truncated version of the same element available in the pom.xml.

It can contain only four child elements: activation, repositories, pluginRepositories, and properties. These elements configure the build system as a whole, instead of any particular project.

It's important to note that values from an active profile in settings.xml will override any equivalent profile values in a pom.xml or profiles.xml file. Profiles are matched by ID.

3.1. Activation

We can use profiles to modify certain values only under given circumstances. We can specify those circumstances using the activation element. Consequently, profile activation occurs when all specified criteria are met:

<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">
    <profiles>
        <profile>
            <id>baeldung-test</id>
            <activation>
                <activeByDefault>false</activeByDefault>
                <jdk>1.8</jdk>
                <os>
                    <name>Windows 10</name>
                    <family>Windows</family>
                    <arch>amd64</arch>
                    <version>10.0</version>
                </os>
                <property>
                    <name>mavenVersion</name>
                    <value>3.0.7</value>
                </property>
                <file>
                    <exists>${basedir}/activation-file.properties</exists>
                    <missing>${basedir}/deactivation-file.properties</missing>
                </file>
            </activation>
        </profile>
    </profiles>
</settings>

There are four possible activators and not all of them need to be specified:

• jdk: activates based on the JDK version specified (ranges are supported)
• os: activates based on operating system properties
• property: activates the profile if Maven detects a specific property value
• file: activates the profile if a given filename exists or is missing

In order to check which profile will activate a certain build, we can use the Maven help plugin:

mvn help:active-profiles

The output will display currently active profiles for a given project:

[INFO] --- maven-help-plugin:3.2.0:active-profiles (default-cli) @ core-java-streams-3 ---
[INFO]
Active Profiles for Project 'com.baeldung.core-java-modules:core-java-streams-3:jar:0.1.0-SNAPSHOT':
The following profiles are active:
 - baeldung-test (source: com.baeldung.core-java-modules:core-java-streams-3:0.1.0-SNAPSHOT)

3.2. Properties

Maven properties can be thought of as named placeholders for a certain value. The values are accessible within a pom.xml file using the ${property_name} notation:

<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">
    <profiles>
        <profile>
            <id>baeldung-test</id>
            <properties>
                <user.project.folder>${user.home}/baeldung-tutorials</user.project.folder>
            </properties>
        </profile>
    </profiles>
</settings>

Four different types of properties are available in pom.xml files:

• Properties using the env prefix return an environment variable value, for example, ${env.PATH}
• Properties using the project prefix return a property value set in the project element of the pom.xml, for example, ${project.version}
• Properties using the settings prefix return the corresponding element’s value from the settings.xml, for example, ${settings.localRepository}
• We may reference all properties available via System.getProperties method in Java directly, for example, ${java.home}
• We may use properties set within a properties element without a prefix, for example, ${junit.version}

3.3. Repositories

Remote repositories contain collections of artifacts that Maven uses to populate our local repository. Different remote repositories may be needed for particular artifacts. Maven searches the repositories enabled under the active profile:

<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">
    <profiles>
        <profile>
            <id>adobe-public</id>
            <repositories>
	        <repository>
	            <id>adobe-public-releases</id>
	            <name>Adobe Public Repository</name>
	            <url>https://repo.adobe.com/nexus/content/groups/public</url>
	            <releases>
	                <enabled>true</enabled>
	                <updatePolicy>never</updatePolicy>
	            </releases>
	            <snapshots>
	                <enabled>false</enabled>
	            </snapshots>
	        </repository>
	    </repositories>
        </profile>
    </profiles>
</settings>

We can use the repository element to enable only release or snapshots versions of artifacts from a specific repository.

3.4. Plugin Repositories

There are two standard types of Maven artifacts – dependencies and plugins. As Maven plugins are a special type of artifact, we may separate plugin repositories from the others:

<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">
    <profiles>
        <profile>
            <id>adobe-public</id>
            <pluginRepositories>
               <pluginRepository>
                  <id>adobe-public-releases</id>
                  <name>Adobe Public Repository</name>
                  <url>https://repo.adobe.com/nexus/content/groups/public</url>
                  <releases>
                      <enabled>true</enabled>
                      <updatePolicy>never</updatePolicy>
                  </releases>
                  <snapshots>
                      <enabled>false</enabled>
                  </snapshots>
	        </pluginRepository>
	    </pluginRepositories>
        </profile>
    </profiles>
</settings>

Notably, the structure of the pluginRepositories element is very similar to the repositories element.

3.5. Active Profiles

The activeProfiles element contains child elements that refer to a specific profile ID. Maven automatically activates any profile referenced here:

<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">
    <activeProfiles>
        <activeProfile>baeldung-test</activeProfile>
        <activeProfile>adobe-public</activeProfile>
    </activeProfiles>
</settings>

In this example, every invocation of mvn is run as though we've added -P baeldung-test,adobe-public to the command line.

4. Settings Level

A settings.xml file is usually found in a couple of places:

• Global settings in Mavens home directory: ${maven.home}/conf/settings.xml
• User settings in the user’s home: ${user.home}/.m2/settings.xml

If both files exist, their contents are merged. Configurations from the user settings take precedence.

4.1. Determine File Location

In order to determine the location of global and user settings, we can run Maven using the debug flag and search for “settings” in the output:

$ mvn -X clean | grep "settings"

[DEBUG] Reading global settings from C:\Program Files (x86)\Apache\apache-maven-3.6.3\bin\..\conf\settings.xml
[DEBUG] Reading user settings from C:\Users\Daniel Strmecki\.m2\settings.xml

4.2. Determine Effective Settings

We can use the Maven help plugin to find out the contents of the combined global and user settings:

mvn help:effective-settings

This describes the settings in XML format:

<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>C:\Users\Daniel Strmecki\.m2\repository</localRepository>
    <pluginGroups>
        <pluginGroup>org.apache.tomcat.maven</pluginGroup>
        <pluginGroup>org.apache.maven.plugins</pluginGroup>
        <pluginGroup>org.codehaus.mojo</pluginGroup>
    </pluginGroups>
</settings>

4.3. Override the Default Location

Maven also allows us to override the location of the global and user settings via the command line:

$ mvn clean --settings c:\user\user-settings.xml --global-settings c:\user\global-settings.xml

We can also use the shorter –s version of the same command:

$ mvn clean --s c:\user\user-settings.xml --gs c:\user\global-settings.xml

5. Conclusion

In this article, we explored the configurations available in Maven's settings.xml file.

We saw how to configure proxies, repositories and profiles.

Next, we looked at the difference between global and user settings files and how to determine which are in use.

Finally, we looked at determining the effective settings used, and overriding default file locations.