Using OSGi services from an Ext plugin is done the same way that Liferay DXP’s
core uses OSGi services: via the com.liferay.registry API provided by the
registry-api bundle. All usages of this API in Liferay DXP’s core can serve as
examples. Here’s a very simple example:
Registry registry = RegistryUtil.getRegistry();
UserService userService = registry.getService(UserService.class);
If (userService != null) {
User user = userService.getCurrentUser();
System.out.println("Current user is " + user.getFirstName() + StringPool.BLANK +
user.getLastName());
}
Remember that OSGi services can come and go at any time. Liferay DXP services,
including UserService, aren’t an exception to this rule. Although it’s
unlikely that UserService becomes unavailable, you must still account for
that possibility. Liferay DXP’s registry API provides ServiceReference and
ServiceTracker, which you can use to simplify dealing with OSGi services. If
you’re familiar with OSGi development, you’ve heard of these classes because the
OSGi framework provides them. Liferay DXP’s versions of these classes wrap the
OSGi ones, so you can use them the same way.
Here’s a smarter version of the above example. Using service trackers takes away much of the pain of having to deal with services that can appear and disappear dynamically:
Registry registry = RegistryUtil.getRegistry();
ServiceTracker<UserService, UserService> tracker = registry.trackServices(UserService.class);
tracker.open();
UserService userService = tracker.getService();
if (userService != null) {
User user = userService.getCurrentUser();
System.out.println("Current user is " + user.getFirstName() + StringPool.SPACE +
user.getLastName());
}
tracker.close();
Remember to open your service trackers before use and close them after use. If
you must use Liferay DXP’s OSGi services in a servlet, for example, it’s a good
idea to open your service trackers in Servlet.init() and close them in
Servlet.destroy().