Chapter 19. Using Maven Archetypes  TOC  Appendix B. Appendix: Sun Specification Alternatives

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Appendix A. Appendix: Settings Details

A.1. Quick Overview

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The settings element in the settings.xml file contains elements used to define values which configure Maven execution. Settings in this file are settings which apply to many projects and which should not be bundled to any specific project, or distributed to an audience. These include values such as the local repository location, alternate remote repository servers, and authentication information. There are two locations where a settings.xml file may live:

  • Maven Installation Directory: $M2_HOME/conf/settings.xml

  • User-specific Settings File: ~/.m2/settings.xml

Here is an overview of the top elements under settings:

Example A.1. Overview of top-level elements in settings.xml

<settings xmlns="http://maven.apache.org/POM/4.0.0"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 
                      http://maven.apache.org/xsd/settings-1.0.0.xsd">
  <localRepository/>
  <interactiveMode/>
  <usePluginRegistry/>
  <offline/>
  <pluginGroups/>
  <servers/>
  <mirrors/>
  <proxies/>
  <profiles/>
  <activeProfiles/>
</settings>


A.2. Settings Details

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A.2.1. Simple Values

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Half of the top-level settings elements are simple values, representing a range of values which configure the core behavior of Maven:

Example A.2. Simple top-level elements in settings.xml

<settings xmlns="http://maven.apache.org/POM/4.0.0"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 
                      http://maven.apache.org/xsd/settings-1.0.0.xsd">
  <localRepository>${user.dir}/.m2/repository</localRepository>
  <interactiveMode>true</interactiveMode>
  <usePluginRegistry>false</usePluginRegistry>
  <offline>false</offline>
  <pluginGroups>
    <pluginGroup>org.codehaus.mojo</pluginGroup>
  </pluginGroups>
  ...
</settings>


The simple top-level elements are:

localRepository

This value is the path of this build system's local repository. The default value is ${user.dir}/.m2/repository.

interactiveMode

true if Maven should attempt to interact with the user for input, false if not. Defaults to true.

usePluginRegistry

true if Maven should use the ${user.dir}/.m2/plugin-registry.xml file to manage plugin versions, defaults to false.

offline

true if this build system should operate in offline mode, defaults to false. This element is useful for build servers which cannot connect to a remote repository, either because of network setup or security reasons

pluginGroups

This element contains a list of pluginGroup elements, each contains a groupId. The list is searched when a plugin is used and the groupId is not provided in the command line. This list contains org.apache.maven.plugins by default.

A.2.2. Servers

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The distributionManagement element of the POM defines the repositories for deployment. However, certain settings such as security credentials should not be distributed along with the pom.xml. This type of information should exist on the build server in the settings.xml.

Example A.3. Server configuration in settings.xml

<settings xmlns="http://maven.apache.org/POM/4.0.0"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 
                      http://maven.apache.org/xsd/settings-1.0.0.xsd">
  ...
  <servers>
    <server>
      <id>server001</id>
      <username>my_login</username>
      <password>my_password</password>
      <privateKey>${usr.home}/.ssh/id_dsa</privateKey>
      <passphrase>some_passphrase</passphrase>
      <filePermissions>664</filePermissions>
      <directoryPermissions>775</directoryPermissions>
      <configuration></configuration>
    </server>
  </servers>
  ...
</settings>


The elements under server are:

id

This is the id of the server (not of the user to login as) that matches the distributionManagement repository element's id.

username, password

These elements appear as a pair denoting the login and password required to authenticate to this server.

privateKey, passphrase

Like the previous two elements, this pair specifies a path to a private key (default is ${user.home}/.ssh/id_dsa) and a passphrase, if required. The passphrase and password elements may be externalized in the future, but for now they must be set plain-text in the settings.xml file.

filePermissions, directoryPermissions

When a repository file or directory is created on deployment, these are the permissions to use. The legal values of each is a three digit number corresponding to *nix file permissions, i.e. 664, or 775.

A.2.3. Mirrors

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Example A.4. Mirror configuration in settings.xml

<settings xmlns="http://maven.apache.org/POM/4.0.0"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 
                      http://maven.apache.org/xsd/settings-1.0.0.xsd">
  ...
  <mirrors>
    <mirror>
      <id>planetmirror.com</id>
      <name>PlanetMirror Australia</name>
      <url>http://downloads.planetmirror.com/pub/maven2</url>
      <mirrorOf>central</mirrorOf>
    </mirror>
  </mirrors>
  ...
</settings>


id, name

The unique identifier of this mirror. The id is used to differentiate between mirror elements.

url

The base URL of this mirror. The build system will use prepend this URL to connect to a repository rather than the default server URL.

mirrorOf

The id of the server that this is a mirror of. For example, to point to a mirror of the Maven central server (http://repo1.maven.org/maven2), set this element to central. This must not match the mirror id.

A.2.4. Proxies

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Example A.5. Proxy configuration in settings.xml

<settings xmlns="http://maven.apache.org/POM/4.0.0"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 
                      http://maven.apache.org/xsd/settings-1.0.0.xsd">
  ...
  <proxies>
    <proxy>
      <id>myproxy</id>
      <active>true</active>
      <protocol>http</protocol>
      <host>proxy.somewhere.com</host>
      <port>8080</port>
      <username>proxyuser</username>
      <password>somepassword</password>
      <nonProxyHosts>*.google.com|ibiblio.org</nonProxyHosts>
    </proxy>
  </proxies>
  ...
</settings>


id

The unique identifier for this proxy. This is used to differentiate between proxy elements.

active

true if this proxy is active. This is useful for declaring a set of proxies, but only one may be active at a time.

protocol, host, port

The protocol://host:port of the proxy, separated into discrete elements.

username, password

These elements appear as a pair denoting the login and password required to authenticate to this proxy server.

nonProxyHosts

This is a list of hosts which should not be proxied. The delimiter of the list is the expected type of the proxy server; the example above is pipe delimited - comma delimited is also common.

A.2.5. Profiles

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The profile element in the settings.xml is a truncated version of the pom.xml profile element. It consists of the activation, repositories, pluginRepositories and properties elements. The profile elements only include these four elements because they concern themselves with the build system as a whole (which is the role of the settings.xml file), not about individual project object model settings.

If a profile is active from settings, its values will override any equivalent profiles which matching identifiers in a POM or profiles.xml file.

A.2.6. Activation

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Activations are the key of a profile. Like the POM's profiles, the power of a profile comes from its ability to modify some values only under certain circumstances; those circumstances are specified via an activation element.

Example A.6. Defining Activation Parameters in settings.xml

<settings xmlns="http://maven.apache.org/POM/4.0.0"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 
                      http://maven.apache.org/xsd/settings-1.0.0.xsd">
  ...
  <profiles>
    <profile>
      <id>test</id>
      <activation>
        <activeByDefault>false</activeByDefault>
        <jdk>1.5</jdk>
        <os>
          <name>Windows XP</name>
          <family>Windows</family>
          <arch>x86</arch>
          <version>5.1.2600</version>
        </os>
        <property>
          <name>mavenVersion</name>
          <value>2.0.3</value>
        </property>
        <file>
          <exists>${basedir}/file2.properties</exists>
          <missing>${basedir}/file1.properties</missing>
        </file>
      </activation>
      ...
    </profile>
  </profiles>
  ...
</settings>


Activation occurs when all specified criteria have been met, though not all are required at once.

jdk

activation has a built in, Java-centric check in the jdk element. This will activate if the test is run under a jdk version number that matches the prefix given. In the above example, 1.5.0_06 will match.

os

The os element can define some operating system specific properties shown above.

property

The profile will activate if Maven detects a property (a value which can be dereferenced within the POM by ${name}) of the corresponding name=value pair.

file

Finally, a given filename may activate the profile by the existence of a file, or if it is missing.

The activation element is not the only way that a profile may be activated. The settings.xml file's activeProfile element may contain the profile's id. They may also be activated explicitly through the command line via a comma separated list after the P flag (e.g. -P test).

To see which profile will activate in a certain build, use the maven-help-plugin. 

mvn help:active-profiles

A.2.7. Properties

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Maven properties are value placeholder, like properties in Ant. Their values are accessible anywhere within a POM by using the notation ${X}, where X is the property. They come in five different styles, all accessible from the settings.xml file:

env.X

Prefixing a variable with env. will return the shell’s environment variable. For example, ${env.PATH} contains the $path environment variable. (%PATH% in Windows.)

project.x

A dot-notated (.) path in the POM will contain the corresponding elements value.

settings.x

A dot-notated (.) path in the settings.xml will contain the corresponding elements value.

Java system properties

All properties accessible via java.lang.System.getProperties() are available as POM properties, such as ${java.home}.

x

Set within a properties element or an external file, the value may be used as ${someVar}.

Example A.7. Setting the ${user.install} property in settings.xml

<settings xmlns="http://maven.apache.org/POM/4.0.0"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 
                      http://maven.apache.org/xsd/settings-1.0.0.xsd">
  ...
  <profiles>
    <profile>
      ...
      <properties>
        <user.install>${user.dir}/our-project</user.install>
      </properties>
      ...
    </profile>
  </profiles>
  ...
</settings>


The property ${user.install} is accessible from a POM if this profile is active.

A.2.8. Repositories

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Repositories are remote collections of projects from which Maven uses to populate the local repository of the build system. It is from this local repository that Maven calls it plugins and dependencies. Different remote repositories may contain different projects, and under the active profile they may be searched for a matching release or snapshot artifact.

Example A.8. Repository Configuration in settings.xml

<settings xmlns="http://maven.apache.org/POM/4.0.0"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 
                      http://maven.apache.org/xsd/settings-1.0.0.xsd">
  ...
  <profiles>
    <profile>
      ...
      <repositories>
        <repository>
          <id>codehausSnapshots</id>
          <name>Codehaus Snapshots</name>
          <releases>
            <enabled>false</enabled>
            <updatePolicy>always</updatePolicy>
            <checksumPolicy>warn</checksumPolicy>
          </releases>
          <snapshots>
            <enabled>true</enabled>
            <updatePolicy>never</updatePolicy>
            <checksumPolicy>fail</checksumPolicy>
          </snapshots>
          <url>http://snapshots.maven.codehaus.org/maven2</url>
          <layout>default</layout>
        </repository>
      </repositories>
      <pluginRepositories>
        ...
      </pluginRepositories>
      ...
    </profile>
  </profiles>
  ...
</settings>


releases, snapshots

These are the policies for each type of artifact, Release or snapshot. With these two sets, a POM has the power to alter the policies for each type independent of the other within a single repository. For example, one may decide to enable only snapshot downloads, possibly for development purposes.

enabled

true or false for whether this repository is enabled for the respective type (releases or snapshots).

updatePolicy

This element specifies how often updates should attempt to occur. Maven will compare the local POMs timestamp to the remote. The choices are: always, daily (default), interval:X (where X is an integer in minutes) or never.

checksumPolicy

When Maven deploys files to the repository, it also deploys corresponding checksum files. Your options are to ignore, fail, or warn on missing or incorrect checksums.

layout

In the above description of repositories, it was mentioned that they all follow a common layout. This is mostly correct. Maven 2 has a default layout for its repositories; however, Maven 1.x had a different layout. Use this element to specify which if it is default or legacy. If you are upgrading from Maven 1 to Maven 2, and you want to use the same repository which was used in your Maven 1 build, list the layout as legacy.

A.2.9. Plugin Repositories

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The structure of the pluginRepositories element block is similar to the repositories element. The pluginRepository elements each specify a remote location of where Maven can find plugins artifacts.

Example A.9. Plugin Repositories in settings.xml

<settings xmlns="http://maven.apache.org/POM/4.0.0"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 
                      http://maven.apache.org/xsd/settings-1.0.0.xsd">
  ...
  <profiles>
    <profile>
      ...
      <repositories>
        ...
      </repositories>
      <pluginRepositories>
        <pluginRepository>
          <id>codehausSnapshots</id>
          <name>Codehaus Snapshots</name>
          <releases>
            <enabled>false</enabled>
            <updatePolicy>always</updatePolicy>
            <checksumPolicy>warn</checksumPolicy>
          </releases>
          <snapshots>
            <enabled>true</enabled>
            <updatePolicy>never</updatePolicy>
            <checksumPolicy>fail</checksumPolicy>
          </snapshots>
          <url>http://snapshots.maven.codehaus.org/maven2</url>
          <layout>default</layout>
        </pluginRepository>
      </pluginRepositories>
      ...
    </profile>
  </profiles>
  ...
</settings>

A.2.10. Active Profiles

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Example A.10. Setting active profiles in settings.xml

<settings xmlns="http://maven.apache.org/POM/4.0.0"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 
                      http://maven.apache.org/xsd/settings-1.0.0.xsd">
  ...
  <activeProfiles>
    <activeProfile>env-test</activeProfile>
  </activeProfiles>
</settings>


The final piece of the settings.xml puzzle is the activeProfiles element. This contains a set of activeProfile elements, which each have a value of a profile id. Any profile id defined as an activeProfile will be active, regardless of any environment settings. If no matching profile is found nothing will happen. For example, if env-test is an activeProfile, a profile in a pom.xml (or profile.xml with a corresponding id it will be active. If no such profile is found then execution will continue as normal.

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Maven: The Definitive Guide by Sonatype, Inc. is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 United States License.
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