HK2 - Dependency Injection Kernel

A light-weight and dynamic dependency injection framework

The Guice/HK2 Bridge

The Guice/HK2 Bridge can be used to inject Guice services into HK2 services or inject HK2 services into Guice services. It can be used bi-directionally as well.


  • A Guice service is a service that is instantiated (created) by Guice
  • An HK2 service is a service that is instantiated (created) by HK2

Injecting Guice services into HK2 services

Guice services can be injected into any injection point in HK2. In order to do this you must tell HK2 about the Guice Injector which has the Guice service definitions. This is accomplished in two steps.

In the first step you should have the ServiceLocator that contains services you wish to be injected with Guice services. You must initialize this ServiceLocator with some required Guice/HK2 bridge services. You can do this using the utility class GuiceBridge. This is a code snippet that initializes a ServiceLocator:


In the second step you must tell your initialized ServiceLocator about the specific Guice Injector(s) that you want it to look for services in. You do this with the GuiceIntoHK2Bridge service that was added in the previous step. The following code snippet adds a Guice Injector to be searched for services when injecting into HK2 services:

  public void tieInjectorToLocator(ServiceLocator aServiceLocator, Injector guiceInjector) {
      GuiceIntoHK2Bridge guiceBridge = aServiceLocator.getService(GuiceIntoHK2Bridge.class);

Any Guice Injector added with the bridgeGuiceInjector method will be searched for services that HK2 cannot otherwise find.

For example, if you have a service called GuiceService that is created by Guice, you can inject it into an HK2 service (called HK2Service) like this:

  public class HK2Service {
      private GuiceService guiceService;

Injecting HK2 services into Guice services

HK2 services can be injected into Guice services. In order to do so, you must use the HK2Inject injection annotation. For example, if you have an HK2 service named HK2Service that is to be injected into a Guice service (called GuiceService) your code would look like this:

  public class GuiceService {
      private HK2Service hk2Service;

In order to do this we have provided an implementation of Module that should be given to Guice when creating the Guice Injector. This implementation of Module is [HK2IntoGuiceBridge][hk2intoguicebridge]. The following code snippet is an example of how you would create a Guice Injector using the [HK2IntoGuiceBridge]hk2intoguicebridgemodule to tell the Guice Injector about the ServiceLocator to use for finding HK2 services:

  Injector injector = Guice.createInjector(
                new HK2IntoGuiceBridge(serviceLocator),
                // application modules);

Any Guice service that can be created with this Injector will now search the provided ServiceLocator when it encounters a service that is injected with the HK2Inject annotation.

Bi-Directional HK2 Guice Bridge

Guice and HK2 can bridge back and forth between each other. The following code example shows how you could accomplish such a thing:

  public Injector createBiDirectionalGuiceBridge(ServiceLocator serviceLocator,
            Module... applicationModules) {
        Module allModules[] = new Module[applicationModules.length + 1];
        allModules[0] = new HK2IntoGuiceBridge(serviceLocator);
        for (int lcv = 0; lcv < applicationModules.length; lcv++) {
            allModules[lcv + 1] = applicationModules[lcv];
        Injector injector = Guice.createInjector(allModules);
        GuiceIntoHK2Bridge g2h = serviceLocator.getService(GuiceIntoHK2Bridge.class);
        return injector;

The above method will create a Guice Injector where services created by Guice can be injected with HK2 services (using the HK2Inject annotation). Also services created by HK2 can be injected with Guice services (using any supported HK2 injection annotation).