CDI ADVANCEDMeta Data & Extensions

@antoine_sd

ANTOINE SABOT-DURAND

• Senior Software Engineer @Red Hat

• Java & OSS :

• CDI co-spec lead

• CDI community development

• Tech Lead on Agorava

• @antoine_sd

MEET CDI SPI

SPI CAN BE SPLIT IN 4 PARTS

1.SPI DEDICATED TO TYPE META-MODEL

WHY HAVING A TYPE META-MODEL?

WHY HAVING A TYPE META-MODEL?Because @Annotations are configuration

WHY HAVING A TYPE META-MODEL?Because @Annotations are configuration

but they are also read-only

WHY HAVING A TYPE META-MODEL?Because @Annotations are configuration

but they are also read-only

as we want to write configuration We need a mutable meta-model

WHY HAVING A TYPE META-MODEL?Because @Annotations are configuration

but they are also read-only

as we want to write configuration We need a mutable meta-model

for annotated types

2.SPI DEDICATED TO CDI META-MODEL

SPI CAN BE USED IN YOUR CODE 1

@Producespublic <K, V> Map<K, V> produceMap(InjectionPoint ip) { if (valueIsNumber(ip.getType())) { return new TreeMap<K, V>(); } return new HashMap<K, V>();}

SPI CAN BE USED IN YOUR CODE 2public abstract class AbstractBean { @Inject Bean<AbstractBean> meta; @Inject Instance<Foo> fooInstances; public Foo getFooWithSameQualifiers() { Annotation[] beanQualifiers = (Annotation[]) meta.getQualifiers().toArray(); Instance<Foo> mySelect = fooInstances.select(beanQualifiers); if (!(mySelect.isUnsatisfied() && mySelect.isAmbiguous())) return mySelect.get(); else throw new IllegalStateException("Foo with same qualifiers not found"); } }

SPI CAN BE USED IN YOUR CODE 3

@ApplicationScoped public class ExampleBean { private void strictListen(@Observes @Qualified Payload evt, EventMetadata meta) { if(meta.getQualifiers().contains(new QualifiedLiteral()) && meta.getType().equals(Payload.class)) System.out.println("Do something"); else System.out.println("ignore"); } }

3. CDI ENTRY POINTS

SPI DEDICATED TO EXTENSIONS

MOST OF THESE SPI ARE EVENTS CONTAINING META MODEL SPI CLASSES

MOST OF THESE SPI ARE EVENTS CONTAINING META MODEL SPI CLASSES

ProcessAnnotatedType

MOST OF THESE SPI ARE EVENTS CONTAINING META MODEL SPI CLASSES

These Events are automatically fired by CDI when application starts and can observed in method included in a CDI extension

CDI EXTENSIONS

CDI EXTENSIONS FOR WHAT ?• A CDI extension can :

• Create / modify :

• Beans

• Injection Target

• Injection Points

• Cancel beans creation

• More generally extensions can modify all CDI context at launch time

TO UNDERSTAND EXTENSIONS• Once application is bootstrapped, the

Bean Manager is in read only mode (no dynamic bean registration)

• Extensions are launch during bootsrap and are based on CDI events

• You only have to @Observes built-in CDI event to create your extensions

• Learn the different events fired at boot time on next slide

CDI 1.1 LIFECYCLE

Before Bean Discovery

Process BeanProcess Annotated

Type

ScanArchive

ApplicationRunning

After Deployment Validation

Before Shutdown Undeploy ApplicationProcess Producer

After Bean Discovery

ProcessInjection Target

Process Observer Method

ProcessInjection Point

Process Bean Attributes

After Type Discovery

Occurs once

occurs for each elts

internal step

Deployment starts

Bean eligibility check

HOW TO BUILD A CDI EXTENSION• Create a class implementing javax.enterprise.inject.spi.Extension

• Add some method that observes CDI lifecyle events to modify Bean Manager meta data

• Add file :META-INF/services/javax.enterprise.inject.spi.Extension

in class path. And put the qualified name of the extension in it

SIMPLE EXAMPLE - VETO JPA ENTITIES

public class VetoEntityExtension implements Extension { void vetoEntites(@Observes @WithAnnotations(Entity.class)ProcessAnnotatedType<?> pat) { pat.veto(); }}

QUESTIONS