@Creatable
public class DAO {

	@Inject
	@Preference(nodePath="/instance")
	IEclipsePreferences preferences;

	@Inject
	@GeminiPersistenceContext(unitName = "configured", properties = {
			@GeminiPersistenceProperty(name = PersistenceUnitProperties.JDBC_DRIVER, valuePref = @Preference(nodePath="/instance", value="jdbc_driver")),
			@GeminiPersistenceProperty(name = PersistenceUnitProperties.JDBC_URL, valuePref = @Preference(nodePath="/instance", value="jdbc_url")),
			@GeminiPersistenceProperty(name = PersistenceUnitProperties.JDBC_USER, valuePref = @Preference(nodePath="/instance", value="jdbc_user")),
			@GeminiPersistenceProperty(name = PersistenceUnitProperties.JDBC_PASSWORD, valuePref = @Preference(nodePath="/instance", value="jdbc_pwd")),
			@GeminiPersistenceProperty(name = PersistenceUnitProperties.LOGGING_LEVEL, value = "FINE"),
			@GeminiPersistenceProperty(name = PersistenceUnitProperties.WEAVING, value = "false"),
			@GeminiPersistenceProperty(name = PersistenceUnitProperties.WEAVING_INTERNAL, value = "false"),
			@GeminiPersistenceProperty(name = GeminiPersistenceProperties.GEMINI_REINIT) })
	private EntityManager em;

	@Inject
	public DAO() {
		preferences.put(GeminiPersistenceProperties.GEMINI_REINIT, "false");
		try {
			preferences.flush();
		} catch (BackingStoreException e) {
			e.printStackTrace();
		}
	}

	public Object void  save(Object dataObj) throws SQLException {
		checkConnection();
		EntityTransaction trx = em.getTransaction();
		trx.begin();
		em.persist(dataObj);
		trx.commit();
	}

	@PreDestroy
	public void destroy() {
		if (em != null && em.isOpen()) {
			em.close();
		}
	}

	private void checkConnection() throws SQLException {
		if (em == null) {
			throw new SQLException(
					"EntityManager is null. Not connected to database!");
		}
	}
}

public class TestSaveDBHandler {

	@Execute
	public void execute(@Named(IServiceConstants.ACTIVE_SHELL) Shell shell,
			DAO dao) throws InvocationTargetException, InterruptedException {

		try {
			// Via injected DAO
			Contact c = BioofficeFactory.eINSTANCE.createContact();
			c.setFirstName("Ludwig");
			c.setLastName("Spitzenstätter via DAO");
			System.out.println("dao=" + dao);
			System.out.println("contact=" + c);
			dao.save(c);
		} catch (Exception e) {
			MessageDialog.openError(shell, "Error persisting Contact",
					"Something went wrong in the DAO \n " + e.getMessage());
		}
	}
}

import org.eclipse.e4.tools.compat.parts.DIHandler;

public class E4TestSaveDBHandler extends DIHandler<TestSaveDBHandler> {

	public E4TestSaveDBHandler() {
		super(TestSaveDBHandler.class);
	}
}

<command
            defaultHandler="handlers.E4TestSaveDBHandler"
            id="TestSaveDBHandler"
            name="TestSaveDBHandler">
       </command>

Caused by: org.eclipse.e4.core.di.InjectionException: Unable to process "TestSaveDBHandler#execute()": no actual value was found for the argument "DAO".
	at org.eclipse.e4.core.internal.di.InjectorImpl.reportUnresolvedArgument(InjectorImpl.java:412)
	at org.eclipse.e4.core.internal.di.InjectorImpl.invokeUsingClass(InjectorImpl.java:239)
	at org.eclipse.e4.core.internal.di.InjectorImpl.invoke(InjectorImpl.java:213)
	at org.eclipse.e4.core.contexts.ContextInjectionFactory.invoke(ContextInjectionFactory.java:90)
	at org.eclipse.e4.tools.compat.parts.DIHandler.execute(DIHandler.java:48)
	at org.eclipse.ui.internal.handlers.HandlerProxy.execute(HandlerProxy.java:290)
	at org.eclipse.ui.internal.handlers.E4HandlerProxy.execute(E4HandlerProxy.java:90)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
	at java.lang.reflect.Method.invoke(Unknown Source)
	at org.eclipse.e4.core.internal.di.MethodRequestor.execute(MethodRequestor.java:56)
	... 37 more

@Inject
	public DAO(MApplication application) {
                application.getContext().set(this.getClass().getName(), this);
		preferences.put(GeminiPersistenceProperties.GEMINI_REINIT, "false");
		try {
			preferences.flush();
		} catch (BackingStoreException e) {
			e.printStackTrace();
		}
	}

@Creatable
public class DAO {

	@Inject
	@Preference
	IEclipsePreferences preferences;



	@Inject
	public DAO() {
		System.out.println("DAO: preferences="+preferences);
	}
}