Maven - (Property|Filter)

A property is used to supplied value of resource files at build time. This process is called filtering.

A property can be:

• one of the values defined in your pom.xml,
• a value defined in the user's settings.xml,
• an environment variable
• a property defined in an external properties file,
• or a system property.

Filtering is dsiable by default. To enable it, you must modify the filtering element of the Pom.xml.

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

<project>
  ....
  <properties>
    <my.filter.value>hello</my.filter.value>
  </properties>
</project>

In src/main/filters/

Example: filter.properties:

# filter.properties
my.filter.value=hello!

The external property file must be defined in the POM.xml

<build>
  <filters>
      <filter>src/main/filters/filter.properties</filter>
  </filters>
.......
</build>

To reference a property from the configuration files, the property name uses the following syntax:

${AliasRootElement.element}

where:

• AliasRootElement is of:
  • pom for Maven - pom.xml - Project Object Model
  • settings for settings.xml
  • env for environment variable
• Element is an element of the XML file

Some elements have default values and then don't need to be explicitly defined.

Example:

• ${pom.name} refers to the name of the project,
• ${pom.version} refers to the version of the project,
• ${pom.build.finalName} refers to the final name of the file created when the built project is packaged,
• ${settings.localRepository} refers to the path of the user's local repository).
• ${env.myEnvironmentVariableName} refers the the environment variable myEnvironmentVariableName

Filtering resources can also get values from system properties built into Java like:

• java.version
• user.home
• …

Properties can also be defined on the command line using the standard Java -D parameter.

Example: To define the property command.line.prop with the value “hello again”

mvn process-resources "-Dcommand.line.prop=hello again"

Process (OS) - Environment Variable

${env.variable_name}

https://books.sonatype.com/mvnref-book/reference/resource-filtering-sect-properties.html

The property values will be supplied when the resource is filtered.

Example: application.properties in the src/main/resources directory

# application.properties
application.name=${pom.name}
application.version=${pom.version}
java.version=${java.version}
command.line.prop=${command.line.prop}

mvn process-resources

• http://books.sonatype.com/mvnref-book/reference/resource-filtering-sect-properties.html