Sonatype

Properties

A large portion of Maven's portability may be attributed to its use of properties. Like properties in Ant or variables in Make, Maven properties represent a value to be set at runtime (as opposed to a hardcoded value like a String or Integer). This is a list of the most common properties in Maven's core.

This is the base directory of the currently running project... where the POM file lives.

• basedirThese properties corrospond to values in the current project's POM settings.

   project.*
    version
    build.*
      directory

• project.groupId
• project.artifactId
• project.version
• project.packaging
• project.build.directory
• project.build.finalName

These properties corrospond to values in the system's settings.xml file. Note that the settings.xml file can be in the Maven installation /conf directory, as well as the current user's home directory (${user.home}) /.m2 directory. Their values are merged, with the user settings winning.

 settings.*
  localRepository

• settings.localRepository

 Environment variable ... highly system specific, but some assumptions can often be made.
 env.*
   PATH
   M2_HOME
   JAVA_HOME

Java runtime's System.properties.

• java.version - Java Runtime Environment version
• java.vendor - Java Runtime Environment vendor
• java.vendor.url - Java vendor URL
• java.home - Java installation directory
• java.vm.specification.version - Java Virtual Machine specification version
• java.vm.specification.vendor - Java Virtual Machine specification vendor
• java.vm.specification.name - Java Virtual Machine specification name
• java.vm.version - Java Virtual Machine implementation version
• java.vm.vendor - Java Virtual Machine implementation vendor
• java.vm.name - Java Virtual Machine implementation name
• java.specification.version - Java Runtime Environment specification version
• java.specification.vendor - Java Runtime Environment specification vendor
• java.specification.name - Java Runtime Environment specification name
• java.class.version - Java class format version number
• java.class.path - Java class path
• java.ext.dirs - Path of extension directory or directories
• os.name - Operating system name
• os.arch - Operating system architecture
• os.version - Operating system version
• file.separator - File separator ("/" on UNIX, "\" on Windows)
• path.separator - Path separator (":" on UNIX, ";" on Windows)
• line.separator - Line separator ("\n" on UNIX and Windows)
• user.name - User's account name
• user.home - User's home directory
• user.dir - User's current working directory

Filtering

Filtering is an integral part of Maven resources, and is a chief reason why resources are seperated from source code (the next is seperation of concerns). Filtering is simple to do in Maven:

<project>
  ...
  <build>
    <resources>
      <resource>
        <directory>src/main/resources</directory>
        <filtering>true</filtering>
      </resource>
    </resources>
  </build>

  <properties>
    <some.property.name>property value!</some.property.name>
  </properties>
  ...
</project>

Now any file under src/main/resources which contains the denotion ${some.property.name} will be replaced by the building property value... in the above case "property value!".

Tips and Tricks

<project>
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.mycompany</groupId>
  <artifactId>prop-test</artifactId>
  <version>1.0-SNAPSHOT</version>
  <packaging>pom</packaging>

  <build>
    <plugins>
      <plugin>
        <artifactId>maven-antrun-plugin</artifactId>
        <executions>
          <execution>
            <phase>validate</phase>
            <goals>
              <goal>run</goal>
            </goals>
            <configuration>
              <tasks>
                <echo>$PATH=${env.PATH}</echo>
              </tasks>
            </configuration>
          </execution>
        </executions>
      </plugin>
    </plugins>
  </build>
</project>

[INFO] Scanning for projects...
[INFO] ----------------------------------------------------------------------------
[INFO] Building Unnamed - com.mycompany:prop-test:pom:1.0-SNAPSHOT
[INFO]    task-segment: [validate]
[INFO] ----------------------------------------------------------------------------
[INFO] [antrun:run {execution: default}]
[INFO] Executing tasks
     [echo] $PATH=/usr/local/bin:/sw/bin:/sw/sbin:/bin:/sbin:/usr/bin:/usr/sbin:/usr/X11R6/bin:/usr/local/maven-2.0.6/bin
[INFO] Executed tasks
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESSFUL
[INFO] ------------------------------------------------------------------------
[INFO] Total time: < 1 second
[INFO] Finished at: Sat Apr 28 11:58:20 CDT 2007
[INFO] Final Memory: 2M/4M
[INFO] ------------------------------------------------------------------------

<project>
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.mycompany.group</groupId>
  <artifactId>parent</artifactId>
  <version>1.1-alpha-4-SNAPSHOT</version>

  <modules>
    <module>sub-project-a</module>
    <module>sub-project-b</module>
  </modules>

  <dependencyManagement>
    <dependencies>
      <dependency>
        <groupId>${groupId}</groupId>
        <artifactId>sub-project-a</artifactId>
        <version>${version}</version>
      </dependency>
      <dependency>
        <groupId>${groupId}</groupId>
        <artifactId>sub-project-b</artifactId>
        <version>${version}</version>
      </dependency>
    </dependencies>
  </dependencyManagement>
  ...
</project>

<project>
  <modelVersion>4.0.0</modelVersion>
  <parent>
    <groupId>com.mycompany.group</groupId>
    <artifactId>parent</artifactId>
    <version>1.1-alpha-4-SNAPSHOT</version>
  </parent>
  <artifactId>sub-project-a</artifactId>

  <dependencies>
    <dependency>
      <groupId>${groupId}</groupId>
      <artifactId>sub-project-b</artifactId>
    </dependency>
  </dependencies>
</project>