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Introduction
CDI is a revolution for Java EE world. This specification is the best one to avoid coupling between classes.
This example simply aims to override bindings at runtime to simplify mocking work.
It uses two kind of mocks:
1) a mock with no implementation in the classloader
2) a mock with an implementation in the classloader
The mock answer from CDI is called alternative.
Annotating @Alternative a class will mean it will replace any implementation if there is no other implementation or if it is forced (through META-INF/beans.xml).
Code explanation
main code
We use an EJB Jouney to modelize a journey where the vehicle and the society can change. Here an EJB is used simply because it simplifies the test. A jouney wraps the vehicle and society information.
We define then two interfaces to inject it in the Journey EJB: Vehicle and Society.
Finally we add an implementation for Scociety interface: LowCostCompanie.
If we don't go further Journey object will not be able to be created because no Vehicle implementation is available.
Note: if we suppose we have a Vehicle implementation, the injected Society should be LowCostCompanie.
test code
The goal here is to test our Journey EJB. So we have to provide a Vehicle implementation: SuperCar.
We want to force the Society implementation (for any reason) by our test implementation: AirOpenEJB.
One solution could simply be to add @Alternative annotation on AirOpenEJB and activate it through the META-INF/beans.xml file.
Here we want to write more explicit code. So we want to replace the @Alternative annotation by @Mock one.
So we simply define an @Mock annotation for classes, resolvable at runtime which is a stereotype (@Stereotype) which replace @Alternative.
Here is the annotation:
@Stereotype // we define a stereotype
@Retention(RUNTIME) // resolvable at runtime
@Target(TYPE) // this annotation is a class level one
@Alternative // it replace @Alternative
public @interface Mock {}
Note: you can add more CDI annotations after @Alternative and it will get the behavior expected (the scope for instance).
So now we have our @Mock annotation which is a stereotype able to replace @Alternative annotation we simply add this annotation to our mocks.
If you run it now you'll have this exception:
javax.enterprise.inject.UnsatisfiedResolutionException: Api type [org.superbiz.cdi.stereotype.Vehicle] is not found with the qualifiers
Qualifiers: [@javax.enterprise.inject.Default()]
for injection into Field Injection Point, field name : vehicle, Bean Owner : [Journey, Name:null, WebBeans Type:ENTERPRISE, API Types:[java.lang.Object,org.superbiz.cdi.stereotype.Journey], Qualifiers:[javax.enterprise.inject.Any,javax.enterprise.inject.Default]]
It means the stereotype is not activated. To do it simply add it to your META-INF/beans.xml:
<alternatives>
<stereotype>org.superbiz.cdi.stereotype.Mock</stereotype>
</alternatives>
Note: if you don't specify AirOpenEJB as @Alternative (done through our mock annotation) you'll get this exception:
Caused by: javax.enterprise.inject.AmbiguousResolutionException: There is more than one api type with : org.superbiz.cdi.stereotype.Society with qualifiers : Qualifiers: [@javax.enterprise.inject.Default()]
for injection into Field Injection Point, field name : society, Bean Owner : [Journey, Name:null, WebBeans Type:ENTERPRISE, API Types:[org.superbiz.cdi.stereotype.Journey,java.lang.Object], Qualifiers:[javax.enterprise.inject.Any,javax.enterprise.inject.Default]]
found beans:
AirOpenEJB, Name:null, WebBeans Type:MANAGED, API Types:[org.superbiz.cdi.stereotype.Society,org.superbiz.cdi.stereotype.AirOpenEJB,java.lang.Object], Qualifiers:[javax.enterprise.inject.Any,javax.enterprise.inject.Default]
LowCostCompanie, Name:null, WebBeans Type:MANAGED, API Types:[org.superbiz.cdi.stereotype.Society,org.superbiz.cdi.stereotype.LowCostCompanie,java.lang.Object], Qualifiers:[javax.enterprise.inject.Any,javax.enterprise.inject.Default]
which simply means two implementations are available for the same injection point (Journey.society).
Conclusion
With CDI it is really easy to define annotations with a strong meaning. You can define business annotations or simply technical annotations to simplify your code (as we did with the mock annotation).
Note: if for instance you used qualifiers to inject societies you could have put all these qualifiers on the mock class or defined a @SocietyMock annotation to be able to inject the same implementation for all qualifiers in your tests.
Output
Running org.superbiz.cdi.stereotype.StereotypeTest
Apache OpenEJB 7.0.0-SNAPSHOT build: 20111030-07:54
http://tomee.apache.org/
INFO - openejb.home = /opt/dev/openejb/openejb-trunk/examples/cdi-alternative-and-stereotypes
INFO - openejb.base = /opt/dev/openejb/openejb-trunk/examples/cdi-alternative-and-stereotypes
INFO - Using 'javax.ejb.embeddable.EJBContainer=true'
INFO - Configuring Service(id=Default Security Service, type=SecurityService, provider-id=Default Security Service)
INFO - Configuring Service(id=Default Transaction Manager, type=TransactionManager, provider-id=Default Transaction Manager)
INFO - Found EjbModule in classpath: /opt/dev/openejb/openejb-trunk/examples/cdi-alternative-and-stereotypes/target/test-classes
INFO - Found EjbModule in classpath: /opt/dev/openejb/openejb-trunk/examples/cdi-alternative-and-stereotypes/target/classes
INFO - Beginning load: /opt/dev/openejb/openejb-trunk/examples/cdi-alternative-and-stereotypes/target/test-classes
INFO - Beginning load: /opt/dev/openejb/openejb-trunk/examples/cdi-alternative-and-stereotypes/target/classes
INFO - Configuring enterprise application: /opt/dev/openejb/openejb-trunk/examples/cdi-alternative-and-stereotypes
INFO - Configuring Service(id=Default Managed Container, type=Container, provider-id=Default Managed Container)
INFO - Auto-creating a container for bean cdi-alternative-and-stereotypes_test.Comp: Container(type=MANAGED, id=Default Managed Container)
INFO - Configuring Service(id=Default Singleton Container, type=Container, provider-id=Default Singleton Container)
INFO - Auto-creating a container for bean Journey: Container(type=SINGLETON, id=Default Singleton Container)
INFO - Enterprise application "/opt/dev/openejb/openejb-trunk/examples/cdi-alternative-and-stereotypes" loaded.
INFO - Assembling app: /opt/dev/openejb/openejb-trunk/examples/cdi-alternative-and-stereotypes
INFO - Jndi(name="java:global/cdi-alternative-and-stereotypes/cdi-alternative-and-stereotypes_test.Comp!org.apache.openejb.BeanContext$Comp")
INFO - Jndi(name="java:global/cdi-alternative-and-stereotypes/cdi-alternative-and-stereotypes_test.Comp")
INFO - Jndi(name="java:global/cdi-alternative-and-stereotypes/cdi-alternative-and-stereotypes.Comp!org.apache.openejb.BeanContext$Comp")
INFO - Jndi(name="java:global/cdi-alternative-and-stereotypes/cdi-alternative-and-stereotypes.Comp")
INFO - Jndi(name="java:global/cdi-alternative-and-stereotypes/Journey!org.superbiz.cdi.stereotype.Journey")
INFO - Jndi(name="java:global/cdi-alternative-and-stereotypes/Journey")
INFO - Jndi(name="java:global/EjbModule162291475/org.superbiz.cdi.stereotype.StereotypeTest!org.superbiz.cdi.stereotype.StereotypeTest")
INFO - Jndi(name="java:global/EjbModule162291475/org.superbiz.cdi.stereotype.StereotypeTest")
INFO - Created Ejb(deployment-id=cdi-alternative-and-stereotypes_test.Comp, ejb-name=cdi-alternative-and-stereotypes_test.Comp, container=Default Managed Container)
INFO - Created Ejb(deployment-id=cdi-alternative-and-stereotypes.Comp, ejb-name=cdi-alternative-and-stereotypes.Comp, container=Default Managed Container)
INFO - Created Ejb(deployment-id=org.superbiz.cdi.stereotype.StereotypeTest, ejb-name=org.superbiz.cdi.stereotype.StereotypeTest, container=Default Managed Container)
INFO - Created Ejb(deployment-id=Journey, ejb-name=Journey, container=Default Singleton Container)
INFO - Started Ejb(deployment-id=cdi-alternative-and-stereotypes_test.Comp, ejb-name=cdi-alternative-and-stereotypes_test.Comp, container=Default Managed Container)
INFO - Started Ejb(deployment-id=cdi-alternative-and-stereotypes.Comp, ejb-name=cdi-alternative-and-stereotypes.Comp, container=Default Managed Container)
INFO - Started Ejb(deployment-id=org.superbiz.cdi.stereotype.StereotypeTest, ejb-name=org.superbiz.cdi.stereotype.StereotypeTest, container=Default Managed Container)
INFO - Started Ejb(deployment-id=Journey, ejb-name=Journey, container=Default Singleton Container)
INFO - Deployed Application(path=/opt/dev/openejb/openejb-trunk/examples/cdi-alternative-and-stereotypes)
INFO - Undeploying app: /opt/dev/openejb/openejb-trunk/examples/cdi-alternative-and-stereotypes