If you want to use Guice with multiple persistence Unit. Then its not much difficult task to do it, Guice's official wiki document says it all refer. But I feel it has missed out most important part from it i.e. to expose dependencies, if those dependencies need to be used outside the scope of give PrivateModule.
Note : I have created a complete working sample with multiple persistent unit refer - https://github.com/pandurangpatil/guice-gwt/ for the code. This sample mainly demonstrates integration of Guice with GWT but I have added multiple persistent unit sample in the same.
Lets take the same example to understand how to use multiple persistent unit. In this sample there are two persistent units Address and User each having one entity Address and Person respectively ( I have taken single entities in each persistent unit for the sake of simplicity). You have separate DAO created to manage each of the persistent unit. In this example we have AddressDao and PearsonDao. As per document you need to bind dependencies with their respective private module.
e.g.
I have created AddressPersistModule and UserPersistModule each of them is separate private module loading Address and User persistence unit respectively and bind Dao in respective module.
public class UserPersistModule extends PrivateModule {
@Override
protected void configure() {
install(new JpaPersistModule("users"));
bind(PersistenceLifeCycleManager.class).annotatedWith(
UserPersistService.class).to(
UserPersistenceLifeCycleManager.class);
expose(PersistenceLifeCycleManager.class).annotatedWith(
UserPersistService.class);
bind(PersonDao.class).asEagerSingleton();
expose(PersonDao.class);
}
}
public class AddressPersistModule extends PrivateModule {
@Override
protected void configure() {
install(new JpaPersistModule("addresses"));
bind(PersistenceLifeCycleManager.class).annotatedWith(
AddressPersistService.class).to(
AddressPersistenceLifeCycleManager.class);
expose(PersistenceLifeCycleManager.class).annotatedWith(
AddressPersistService.class);
bind(AddressDao.class).asEagerSingleton();
expose(AddressDao.class);
}
}
In respective Dao you can inject EntityManager, and Guice will take care of injecting respective EntityManager for required Persistent Unit. (Note: you will find some different mechanism in above mentioned sample code. but even if you inject just EntityManager it will work seamlessly as per mentioned in document).
Now in above code you will notice we have to expose AddressDao and PersonDao from their respective private modules. Because of which those dependencies will be available globally in given parent injector.
Now you can create the injector like
Injector injector = Guice.createInjector( new UserPersistModule(), new AddressPersistModule(), ... any other modules );
You will have other dependencies configured in different modules and you can inject exposed private module dependencies with them. In this way you can have service class which will have AddressDao and PersonDao injected into it and you can use them at single place. Refer below code
public class PersonService {
@Inject
private Injector injector;
public boolean savePerson(Person p) {
PersonDao pd = injector.getInstance(PersonDao.class);
pd.savePerson(p);
return true;
}
.
.
.
.
public boolean saveAddresss(String personId, List<Address> addresses) {
AddressDao ad = injector.getInstance(AddressDao.class);
for (Address address : addresses) {
if (address.getId() == null || "".equals(address.getId())) {
address.setId(java.util.UUID.randomUUID().toString());
}
address.setPersonId(personId);
ad.saveAddress(address);
}
return true;
}
}