Activiti get users by group id - alfresco

Question

I need to send an email notification to all of the group members on a new task assignment. I have created a TaskListener in which I am trying to get all the users by group id. But every time it returns empty user list.
IdentityService is = Context.getProcessEngineConfiguration().getIdentityService();
List<User> users = is.createUserQuery().memberOfGroup("2007").list();
LOGGER.info("The users are: " +users); // Always prints []
Also, I have following dependencies in my pom.xml
<dependency>
<groupId>com.activiti</groupId>
<artifactId>activiti-app-logic</artifactId>
<version>1.6.2</version>
</dependency>
<dependency>
<groupId>com.activiti</groupId>
<artifactId>activiti-app-data</artifactId>
<version>1.6.2</version>
</dependency>
<dependency>
<groupId>com.activiti</groupId>
<artifactId>activiti-dmn-engine</artifactId>
<version>1.6.2</version>
</dependency>
<dependency>
<groupId>com.activiti</groupId>
<artifactId>activiti-app-model</artifactId>
<version>1.6.2</version>
</dependency>
<dependency>
<groupId>org.apache.commons</groupId>
<artifactId>commons-email</artifactId>
<version>1.1</version>
</dependency>
should I have the org.activiti in my pom.xml instead of com.activiti?
Let me know if there is any other/better way to send notification to the group.
Thanks for your time

Answer 1

I use this way of getting list of users:
Set<String> users_list = authorityService.getContainedAuthorities(AuthorityType.USER, "yourGroupName", false);
Returns collection of all contained authorities - USERs in you group.
See method description: https://dev.alfresco.com/resource/docs/java/org/alfresco/service/cmr/security/AuthorityService.html#getContainedAuthorities-org.alfresco.service.cmr.security.AuthorityType-java.lang.String-boolean-
When you have such users list, you can get NodeRef of each user and get his e-mail address from NodeRef properties like this:
NodeRef user = personService.getPerson("userName");
String email = nodeService.getProperty(user, "email");
Hope it helps.

Answer 2

For custom event notification (i.e. task assignment) a task listener might help you.
PS: you cannot use com.activiti.classes unless you have bought a valid license.