J2Ee 7 Cdi 05.05.2015 Shadowblind

Front 1

What means CDI?

Back 1

Context and dependency injection.

Front 2

What are the main concepts behind CDI?

Back 2

IoC, Loose coupling, dependency injection and scope.

Front 3

Decoupling goes further with CDI by adding what ?

Back 3

Interceptor, decorator and event.

Front 4

What means IoC ?

Back 4

Inversion of control, container takes control of your business code and provides technical services such as security and transaction management

Front 5

What means container takes control of you business code?

Back 5

Container manage lifecycle of components and bring dependency injection and configuration to components

Front 6

List some JEE components ?

Back 6

Enterprise Java bean, servlet, soap web services, REST web services, entities, managed bean

Front 7

What's a managed bean?

Back 7

It's a container managed object that support only a small set of basic services,such as dependency injection, resource injection and lifecycle management

Front 8

What are the main differences between POJO, JavaBean and Enterprise Java Bean ?

Back 8

POJO are classes that run in JVM, JavaBean are POJO that follow certain patterns such as a default constructor, naming conventions for getters and setters etc... Enterprise JavaBean are executed in the container and follow certain rulles

Front 9

What are the main differences between POJO, JavaBean and JEE components ?

Back 9

POJO are classes that run in JVM, JavaBean are POJO that follow certain patterns such as a default constructor, naming conventions for getters and setters etc... JEE components are executed in a container (e.g. Enterprise JavaBean in EJB container) that supplies some services

Front 10

What is resource injection?

Back 10

It was introduced in JEE 5, it inject container resources such as EJB, data source, entity manager, JMS FACTORY into defined components such as EJB, servlet and JSP backend bean.

Front 11

List at least 3 JEE 7 containers

Back 11

EJB, web and CDI container.

Front 12

How CDI manages lifecycle of beans?

Back 12

Back (Definition)

Front 13

List 4 main predefined scopes of CDI

Back 13

Request, session, conversation, application.

Front 14

What's the original meaning of IoC ?

Back 14

The control of creating the dependency between Beans is inverted because it’s given to an external class, not the class itself

Front 15

What makes CDI dependency injection type safe?

Back 15

It uses annotation instead of XML.

Front 16

Does CDI's DI requires setter and getter for an attribute to work? Can a private attribute be injected?

Back 16

Getter and setter are not necessary for DI.

The attribute can be private.

Front 17

Can there be more than one constructor injection point?

Back 17

No, only one constructor injection point is allowed in CDI.

Front 18

When a qualifier is required?

Back 18

When more than one implementations exist, it's necessary to indicate which one to inject by using a qualifier. With out any qualifier at injection point or bean definition, the @default one is implicitly used on those places.

Front 19

What's unsatisfied dependency and ambiguous dependency?

Back 19

At system initiation, container must identify exactly one bean per injection point, if no bean or more than one bean satisfy a injection point, it will not deploy the application and inform you unsatisfied or ambiguous dependency .

Front 20

What's a qualifier?

Back 20

A qualifier represents some semantics associated with a type that is satisfied by some implementation of that

type. It is a user-defined annotation, itself annotated with @javax.inject.Qualifer. It's then used on an injection point to indicate which implementation is required.

Front 21

What's the problem with qualifier? How to resolve it?

Back 21

We might need to define many qualifiers which is too verbose.

We can use qualifier with members or multiple qualifier together.

Front 22

What's an Alternative?

Back 22

Alternatives are beans annotated with the special qualifier javax.enterprise.inject.Alternative. By default

alternatives are disabled and need to be enabled in the beans.xml descriptor to make them available for instantiation

and injection. You can have one beans.xml per deployment environment.

Front 23

Can we inject POJO? How to inject a POJO?

Back 23

If an archive does not have a beans.xml under the META-INF directory, CDI will not

trigger bean discovery and POJOs will not be able to be treated as beans and, thus, be injectable. The only way to be

able to inject POJOs is to use producer fields or producer methods annotated with @Produces.

Front 24

What's the scope of an session context and its beans?

Back 24

An HTTP session

Front 25

Give an example of use of producer and injection point API.

Back 25

create a producer method that uses the InjectionPoint API to configure the right logger based on the class name.

Front 26

How to clean up object created by producer?

Back 26

disposer method allows the

application to perform the customized cleanup of an object returned by a producer method.

Front 27

List the scopes of web tier

Back 27

Request, session, application.

Front 28

List build in scopes of CDI.

Back 28

Request, session, application, conversation scope and dependent pseudo-scope (@Dependent).

Front 29

What's an interceptor?

Back 29

It's used to interpose business method invocation, managed bean support AOP-like functionality by providing ability to intercept method invocation through interceptor. Container is a chains of interceptors which intercept business method call and apply different services.

Front 30

What's mandatory for CDI?

Back 30

The deployment descriptor beans.xml is mandatory. CDI need it to identify beans in the class path, it's called the bean discovery.

Front 31

What's done at deployment time of CDI?

Back 31

Bean discovery: for each jar or war, CDI looks for the beans.xml inside the META-INF or WEB-INF directory, it turn the POJO into CDI beans.

Front 32

What's difference between the specification Dependency Injection and the specification Context dependency injection?

Back 32

These two specifications were complementary and one could not be used without the other in Java EE. Dependency

Injection for Java defined a set of annotations (@Inject, @Named, @Qualifier, @Scope, and @Singleton) mainly used

for injection. CDI gave semantics to DI and added many more features such as context management, events,

decorators, and enhanced interceptors.

Front 33

List some interceptor

Back 33

@Transactional

Front 34

List some annotation related to lifecycle management

Back 34

@PostConstruct

Front 35

How to inject a reference to a bean?

Back 35

Annotate the reference with @Inject

Front 36

What conditions a bean needs to be treated as an CDI bean?

Back 36

According to the CDI 1.1 specification, the container treats any class that satisfies the following conditions as a

CDI Bean:

•It is not a non-static inner class.

•It is a concrete class, or is annotated @Decorator, and

•It has a default constructor with no parameters, or it declares a constructor annotated

@Inject.

Front 37

List 4 main predefined scopes of CDI

Back 37

Request, session, conversation, application.

Front 38

What's the original meaning of IoC ?

Back 38

The control of creating the dependency between Beans is inverted because it’s given to an external class, not the class itself

Front 39

What makes CDI dependency injection type safe?

Back 39

It uses annotation instead of XML.

Front 40

Does CDI's DI requires setter and getter for an attribute to work? Can a private attribute be injected?

Back 40

Getter and setter are not necessary for DI.

The attribute can be private.

Front 41

Can there be more than one constructor injection point?

Back 41

No, only one constructor injection point is allowed in CDI.

Front 42

When a qualifier is required?

Back 42

When more than one implementations exist, it's necessary to indicate which one to inject by using a qualifier. With out any qualifier at injection point or bean definition, the @default one is implicitly used on those places.

Front 43

What's unsatisfied dependency and ambiguous dependency?

Back 43

At system initiation, container must identify exactly one bean per injection point, if no bean or more than one bean satisfy a injection point, it will not deploy the application and inform you unsatisfied or ambiguous dependency .

Front 44

What's a qualifier?

Back 44

A qualifier represents some semantics associated with a type that is satisfied by some implementation of that

type. It is a user-defined annotation, itself annotated with @javax.inject.Qualifer. It's then used on an injection point to indicate which implementation is required.

Front 45

What's the problem with qualifier? How to resolve it?

Back 45

We might need to define many qualifiers which is too verbose.

We can use qualifier with members or multiple qualifier together.

Front 46

What's an Alternative?

Back 46

Alternatives are beans annotated with the special qualifier javax.enterprise.inject.Alternative. By default

alternatives are disabled and need to be enabled in the beans.xml descriptor to make them available for instantiation

and injection. You can have one beans.xml per deployment environment.

Front 47

Can we inject POJO? How to inject a POJO?

Back 47

If an archive does not have a beans.xml under the META-INF directory, CDI will not

trigger bean discovery and POJOs will not be able to be treated as beans and, thus, be injectable. The only way to be

able to inject POJOs is to use producer fields or producer methods annotated with @Produces.

Front 48

What's the scope of an session context and its beans?

Back 48

An HTTP session

Front 49

Give an example of use of producer and injection point API.

Back 49

create a producer method that uses the InjectionPoint API to configure the right logger based on the class name.

Front 50

How to clean up object created by producer?

Back 50

disposer method allows the

application to perform the customized cleanup of an object returned by a producer method.

Front 51

List the scopes of web tier

Back 51

Request, session, application.

Front 52

List build in scopes of CDI.

Back 52

Request, session, application, conversation scope and dependent pseudo-scope (@Dependent). CDI brought web tier and service tier together by giving then meaningful scopes. A bean is bound to an context since creation until it's removed by the container.

Front 53

When application scope is used?

Back 53

It's useful for helper and utility class, or for objects that hold the data shared by the entire application.

Front 54

When to use session scope?

Back 54

It's used for objects that are needed for the entire session, such as user's preferences and login credentials.

Front 55

When to use request scope?

Back 55

It's used for services class or JSF backend beans that are only needed for the duration of an HTTP request.

Front 56

When to use conversation scope?

Back 56

It spans between multiple invocation inside the session boundary with starting and ending point determined by the application. Conversations are used across multiple pages as part of multistep workflow such as navigating through a

wizard or buying items and checking out of an online store.

Front 57

When to use dependent scope?

Back 57

It's the default scope of CDI, a dependent bean is instantiated when

the object it belongs to is created, and destroyed when the object it belongs to is destroyed.

Front 58

Beans of which scope must be serializable? Why?

Back 58

Session scope or conversation scope.

Because container passivate those beans time to time.

Front 59

What's an interceptor?

Back 59

It's used to interpose business method invocation, managed bean support AOP-like functionality by providing ability to intercept method invocation through interceptor. Container is a chains of interceptors which intercept business method call and apply different services.

Front 60

What's @Named?

Back 60

It's a CDI build-in qualifier. It's used outside Java, in expression language in JSF pages for example, annotation is not available.

Front 61

List the four types of interceptor.

Back 61

Method level, constructor level, timeout method and life-cycle callback interceptor.

Front 62

Where can interceptor be defined?

Back 62

Except constructor level, interceptor can be defined in the target bean.

Front 63

What's mandatory for CDI?

Back 63

The deployment descriptor beans.xml is mandatory. CDI need it to identify beans in the class path, it's called the bean discovery.

Front 64

What's done at deployment time of CDI?

Back 64

Bean discovery: for each jar or war, CDI looks for the beans.xml inside the META-INF or WEB-INF directory, it turn the POJO into CDI beans.

Front 65

What's difference between the specification Dependency Injection and the specification Context dependency injection?

Back 65

These two specifications were complementary and one could not be used without the other in Java EE. Dependency

Injection for Java defined a set of annotations (@Inject, @Named, @Qualifier, @Scope, and @Singleton) mainly used

for injection. CDI gave semantics to DI and added many more features such as context management, events,

decorators, and enhanced interceptors.

Front 66

List some interceptor

Back 66

@Transactional

Front 67

List some annotation related to lifecycle management

Back 67

@PostConstruct

Front 68

How to inject a reference to a bean?

Back 68

Annotate the reference with @Inject

Front 69

What conditions a bean needs to be treated as an CDI bean?

Back 69

According to the CDI 1.1 specification, the container treats any class that satisfies the following conditions as a

CDI Bean:

•It is not a non-static inner class.

•It is a concrete class, or is annotated @Decorator, and

•It has a default constructor with no parameters, or it declares a constructor annotated

@Inject.