Specify system property to Maven project

Is there a way ( I mean how do I ) set a system property in a maven project?

I want to access a property from my test and my webapp ( running locally ) and I know I can use a java system property.

Should I put that in ./settings.xml or something like that?

Context

I took an open source project and managed to change the db configuration to use JavaDB

Now, in the jdbc url for JavaDB, the location of the database could be specified as the full path ( see: this other question )

Or a system property: derby.system.home

I have the code working already, but currently it is all hardcoded to:

 jdbc:derby:/Users/oscarreyes/javadbs/mydb

And I want to remove the full path, to leave it like:

 jdbc:derby:mydb

To do that I need to specify the system property ( derby.system.home ) to maven, but I don't know how.

The test are performed using junit ( I don't see any plugin in pom.xml ) and the web app runs with the jetty plugin.

Specifying the system property in the command line seems to work for jetty, but I'm not sure if that's something practical ( granted some other users may run it from eclipse/idea/ whatever )

Is there a way ( I mean how do I ) set a system property in a maven project? I want to access a property from my test [...]

You can set system properties in the Maven Surefire Plugin configuration (this makes sense since tests are forked by default). From Using System Properties:

<project>
  [...]
  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-surefire-plugin</artifactId>
        <version>2.5</version>
        <configuration>
          <systemPropertyVariables>
            <propertyName>propertyValue</propertyName>
            <buildDirectory>${project.build.directory}</buildDirectory>
            [...]
          </systemPropertyVariables>
        </configuration>
      </plugin>
    </plugins>
  </build>
  [...]
</project>

and my webapp ( running locally )

Not sure what you mean here but I'll assume the webapp container is started by Maven. You can pass system properties on the command line using:

mvn -DargLine="-DpropertyName=propertyValue"

Update: Ok, got it now. For Jetty, you should also be able to set system properties in the Maven Jetty Plugin configuration. From Setting System Properties:

<project>
  ...
  <plugins>
    ...
      <plugin>
        <groupId>org.mortbay.jetty</groupId>
        <artifactId>maven-jetty-plugin</artifactId>
        <configuration>
         ...
         <systemProperties>
            <systemProperty>
              <name>propertyName</name>
              <value>propertyValue</value>
            </systemProperty>
            ...
         </systemProperties>
        </configuration>
      </plugin>
  </plugins>
</project>

properties-maven-plugin plugin may help:

<plugin>
    <groupId>org.codehaus.mojo</groupId>
    <artifactId>properties-maven-plugin</artifactId>
    <version>1.0.0</version>
    <executions>
        <execution>
            <goals>
                <goal>set-system-properties</goal>
            </goals>
            <configuration>
                <properties>
                    <property>
                        <name>my.property.name</name>
                        <value>my property value</value>
                    </property>
                </properties>
            </configuration>
        </execution>
    </executions>
</plugin>