Using OSGi Services from EXT Plugins

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().

Calling Non-OSGi Code that Uses OSGi Services

OSGi Basics For Liferay Development

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