Reading properties file from Maven POM file

Question

I have Maven POM file with some configuration and in the section plugins, I have maven tomcat plugin with some configuration like this:

<configuration>
   <url>http://localhost:8080/manager/html</url>
   <server>tomcat</server>
</configuration>

I'd like to export url setting to some property file for example tomcat.properties with that key:

url=http://localhost:8080/manager/html

And how can I read this key back in my POM file?

Solution 1

Maven allows you to define properties in the project's POM. You can do this using a POM file similar to the following:

<project>
    ...
    <properties>
        <server.url>http://localhost:8080/manager/html</server.url>
    </properties>
    ...
    <build>
        <plugins>
            <plugin>
            ...
                <configuration>
                    <url>${server.url}</url>
                    <server>tomcat</server>
                </configuration>
            ...
            </plugin>
        </plugins>
    </build>
</project>

You can avoid specifying the property within the properties tag, and pass the value from the command line as:

mvn -Dserver.url=http://localhost:8080/manager/html some_maven_goal

Now, if you don't want to specify them from the command line and if you need to further isolate these properties from the project POM, into a properties file, then you'll need to use the Properties Maven plugin, and run it's read-project-properties goal in the initialize phase of the Maven lifecycle. The example from the plugin page is reproduced here:

<project>
  <build>
    <plugins>
      <plugin>
        <groupId>org.codehaus.mojo</groupId>
        <artifactId>properties-maven-plugin</artifactId>
        <version>1.0-alpha-2</version>
        <executions>
           <!-- Associate the read-project-properties goal with the initialize phase, to read the properties file. -->
          <execution>
            <phase>initialize</phase>
            <goals>
              <goal>read-project-properties</goal>
            </goals>
            <configuration>
              <files>
                <file>etc/config/dev.properties</file>
              </files>
            </configuration>
          </execution>
        </executions>
      </plugin>
    </plugins>
  </build>
</project>

Solution 2

Complete working example available at: http://hg.defun.work/exp/file/tip/maven/properties

Here essential part of pom.xml:

<plugins>
  <plugin>
    <groupId>org.codehaus.mojo</groupId>
    <artifactId>properties-maven-plugin</artifactId>
    <version>1.0-alpha-2</version>
    <executions>
      <execution>
        <phase>initialize</phase>
        <goals>
          <goal>read-project-properties</goal>
        </goals>
      </execution>
    </executions>
    <configuration>
      <files>
        <file>dev.properties</file>
      </files>
    </configuration>
  </plugin>

  <plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-antrun-plugin</artifactId>
    <version>1.6</version>
    <executions>
      <execution>
        <phase>compile</phase>
        <goals>
          <goal>run</goal>
        </goals>
        <configuration>
          <target>
            <echo>project.build.sourceEncoding is "${project.build.sourceEncoding}"</echo>
            <echo>foo is "${foo}"</echo>
            <echo>with-spaces is "${with-spaces}"</echo>
            <echo>existent.property is "${existent.property}"</echo>
            <echo>nonexistent.property is "${nonexistent.property}"</echo>
          </target>
        </configuration>
      </execution>
    </executions>
  </plugin>
</plugins>

As you can see properties-maven-plugin still at alpha stage, that is why I hate Maven as build tools...

Solution 3

It is not actually possible to load properties from a file using the instructions in the accepted answer as these properties are not available in the pom file though they can be used for filtering. Minimal counter example:

In pom.xml:

<build>
  <plugins>
    <plugin>
      <groupId>org.codehaus.mojo</groupId>
      <artifactId>properties-maven-plugin</artifactId>
      <version>1.0-alpha-2</version>
      <executions>
        <!-- Associate the read-project-properties goal with the initialize phase, to read the properties file. -->
        <execution>
          <!-- Apart from this test, the phase must be initialize -->
          <phase>validate</phase>
          <goals>
            <goal>read-project-properties</goal>
          </goals>
          <configuration>
            <files>
              <file>dev.properties</file>
            </files>
          </configuration>
        </execution>
      </executions>
    </plugin>
    <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-antrun-plugin</artifactId>
      <version>1.6</version>
      <executions>
        <execution>
          <phase>validate</phase>
          <goals>
            <goal>run</goal>
          </goals>
          <configuration>
            <target>
              <echo>Displaying value of properties</echo>
              <echo>[foo] ${foo}</echo>
            </target>
          </configuration>
        </execution>
      </executions>
    </plugin>
  </plugins>
</build>

Having in dev.properties:

foo=bar

Then runnin the command mvn validate produces output:

 [echo] Displaying value of properties
 [echo] [foo] bar