Quick Overview
The settings element in the settings.xml file contains elements used to define values which configure Maven execution in various ways, like the pom.xml, but 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:
* The Maven install: $M2_HOME/conf/settings.xml
* A user's install: ${user.home}/.m2/settings.xml
Here is an overview of the top elements under settings:
xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0
http://maven.apache.org/xsd/settings-1.0.0.xsd">
Settings Details
Simple Values
Half of the top-level settings elements are simple values, representing a range of values which describe elements of the build system that are active full-time.
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http://maven.apache.org/xsd/settings-1.0.0.xsd">
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* localRepository: This value is the path of this build system's local repository. The default value is ${user.home}/.m2/repository. This element is especially useful for a main build server allowing all logged-in users to build from a common local 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.home}/.m2/plugin-registry.xml file to manage plugin versions, defaults to false. Note that for the current version of Maven 2.0, the plugin-registry.xml file should not be depended upon. Consider it dormant for now.
* 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 automatically contains org.apache.maven.plugins and org.codehaus.mojo. For example, given the above settings the Maven command line may execute org.mortbay.jetty:jetty-maven-plugin:run with the truncated command:
mvn jetty:run
Servers
The repositories for download and deployment are defined by the repositories and distributionManagement elements of the POM. However, certain settings such as username and password should not be distributed along with the pom.xml. This type of information should exist on the build server in the settings.xml.
xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0
http://maven.apache.org/xsd/settings-1.0.0.xsd">
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* id: This is the ID of the server (not of the user to login as) that matches the id element of the repository/mirror that Maven tries to connect to.
* 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 corrosponding to *nix file permissions, ie. 664, or 775.
Note: If you use a private key to login to the server, make sure you omit the
Password Encryption
A new feature - server password and passphrase encryption has been added to 2.1.x and 3.0 trunks. See details on this page
Mirrors
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http://maven.apache.org/xsd/settings-1.0.0.xsd">
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* id, name: The unique identifier and user-friendly name of this mirror. The id is used to differentiate between mirror elements and to pick the corresponding credentials from the
* url: The base URL of this mirror. The build system will use this URL to connect to a repository rather than the original repository URL.
* mirrorOf: The id of the repository that this is a mirror of. For example, to point to a mirror of the Maven central repository (http://repo1.maven.org/maven2/), set this element to central. More advanced mappings like repo1,repo2 or *,!inhouse are also possible. This must not match the mirror id.
For a more in-depth introduction of mirrors, please read the Guide to Mirror Settings.
Proxies
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http://maven.apache.org/xsd/settings-1.0.0.xsd">
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* 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, seperated 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.
Profiles
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 concerns 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 equivalently ID'd profiles in a POM or profiles.xml file.
Activation
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.
xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0
http://maven.apache.org/xsd/settings-1.0.0.xsd">
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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. Ranges are also supported as of Maven 2.1. See the maven-enforcer-plugin for more details about supported ranges.
* os: The os element can define some operating system specific properties shown above. See the maven-enforcer-plugin for more details about OS values.
* 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
Properties
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:
1. 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).
2. project.x: A dot (.) notated path in the POM will contain the corresponding element's value. For example:
3. settings.x: A dot (.) notated path in the settings.xml will contain the corresponding element's value. For example:
4. Java System Properties: All properties accessible via java.lang.System.getProperties() are available as POM properties, such as ${java.home}.
5. x: Set within a
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http://maven.apache.org/xsd/settings-1.0.0.xsd">
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The property ${user.install} is accessible from a POM if this profile is active.
Repositories
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.
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http://maven.apache.org/xsd/settings-1.0.0.xsd">
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* 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 POM's timestamp (stored in a repository's maven-metadata file) 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.
Plugin Repositories
Repositories are home to two major types of artifacts. The first are artifacts that are used as dependencies of other artifacts. These are the majority of plugins that reside within central. The other type of artifact is plugins. Maven plugins are themselves a special type of artifact. Because of this, plugin repositories may be separated from other repositories (although, I have yet to hear a convincing argument for doing so). In any case, 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 new plugins.
Active Profiles
xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0
http://maven.apache.org/xsd/settings-1.0.0.xsd">
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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, reguardless 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 corrosponding id will be active. If no such profile is found then execution will continue as normal.
