Exploring the power of CDI in 50 minutes

Exploring the power of CDI in 50 minutes

My Session at Java2Days 2016 @ Sofia, Bulgaria

http://2016.java2days.com/agenda/

Bc1014dd893a5888c57be34985c70906?s=128

Ahmad Gohar

November 17, 2016
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Transcript

  1. EXPLORING THE POWER OF CDI IN 50 MINUTES AHMAD GOHAR

    SOFTWARE ARCHITECT & TECHNICAL TEAM LEAD, IBM Java2Days
  2. GOHAR , AHMAD NABIL • Software Architect & Technical Team

    Lead (9Y.) | CIC, IBM. • Duke Award Winner 2016. • IBM/Open Group Certified Experienced IT Specialist. • M.Sc. in Information System, FCI, Egypt. • MIBA in Global Management, ESLSCA, France. • OCEJPA | OCPWCD | OCPJP | OCP PL/SQL | MCP(s). • JAVA Community Process (JCP) Member. • Blogger Author and Academic Researcher.
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  5. INTRODUCTION TO CDI JSR 299: Contexts and Dependency Injection for

    the Java EE platform
  6. Q : What is the old name of the CDI

    ?
  7. WHAT IS CDI (JSR 299)? • Java Specification Requests •

    JSR is a document of a proposed specification used in the Java Community Process (JCP). • Classes specify what their dependencies • NOT how to obtain them (container responsibility)
  8. COMMON DEPENDENCY INJECTION FRAMEWORKS • Spring • Guice • Seam

    • EJB 3.X • CDI
  9. CDI IS MORE THAN A FRAMEWORK • It’s a whole,

    rich programming model • The theme of CDI is loosecoupling with strong typing. • A bean specifies only the type and semantics of other beans it depends upon • It need not be aware of the actual lifecycle, concrete implementation, threading model or other clients of any bean it interacts with • Even better, the concrete implementation, lifecycle and threading model of a bean may vary according to the deployment scenario, without affecting any client • This loose-coupling makes your code easier to maintain
  10. GETTING OUR FEET WET CDI First Example

  11. • http://ansgohar.blogspot.com/2016/09/create-first-cdi-application.html

  12. • http://ansgohar.blogspot.com/2016/09/create-first-cdi-application.html

  13. AUTOMATIC BEAN DISCOVERY • • How can container scan bean?

    • By detecting the presence of “beans.xml” in application archive • For WAR file, the “beans.xml” is under WEB-INF directory • For JAR file, the “beans.xml” is under META-INF directory • • “beans.xml” • It is not for declaring beans (like in Spring) • It can be empty • Used for some other purposes (like declaring an alternative)
  14. GETTING OUR FEET WET EJB Simple Example

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  16. GETTING OUR FEET WET Injecting EJB using CDI

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  18. CDI BEANS & INJECTION POINT CDI Beans

  19. WHAT IS A BEAN ANYWAY? • Many forms of a

    “bean” already exist. So which bean arewe talking about? • JSF bean • EJB bean • Spring bean • Seam bean • Guice bean • CDI bean • Java EE needs a unified bean definition • Managed Bean 1.0 specification in Java EE 6 provides it
  20. WHAT ABOUT MANAGED, EJB, REST, CDI BEAN? • Managed Beans

    are container-managed POJOs • Lightweight component model • Instances are managed by the container • You could see everything as a Managed Bean with extra services • • An EJB is a Managed Bean with • Transaction support • Security • Thread safety • Persistence • • A REST service is a Managed Bean with • HTTP support • • A CDI bean is a Managed Bean with • CDI services (explained in the next slide)
  21. CDI BEANS & INJECTION POINT Injection Point

  22. MANAGED BEAN  CDI BEAN

  23. Q : How to Inject CDI Beans (Injection Point) ?

  24. CDI INJECTION POINT • Use @Inject <Java-Type> <variable> for field

    injection • <Java-Type> can be Java interface • Bean can be injected at “Injection points” • Field • Method parameter • Method can be • Constructor (useful for created immutable object) • Initializer • Setter method • Producer • Observer
  25. INJECTING INTERFACE

  26. CDI INJECTION POINT

  27. CDI INJECTION POINT

  28. QUALIFIERS, ALTERNATIVES, PROGRAMMATICALLY LOOKUP Qualifiers

  29. Q : What is the result of injecting CDI beans

    that :- 1- have single Implementation ? 2- have no Implementation ? 3- have multiple Implementation ?
  30. WHAT IS A QUALIFIER? • For a given bean type

    (class or interface), there may be multiple beans which implement the type (in the classpath) • For an interface, there could be multiple implementations • For a class, there could be multiple child types • Ambiguity error will result • A qualifier is an annotation that lets a client choose one between multiple candidates of a certain type • Make type more specific • Assigns semantic meaning • Injected type is identified by • Qualifier(s) + Java type
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  35. QUALIFIER AND TYPE SAFETY (STRONG TYPING) • Qualifier + Java

    type makes a composite type (extended type) • Again, think of a Qualifier as a type • Qualifiers make type safe injection possible • Qualifiers replace “look-up via string-based names” • Qualifier and Type Safety (Strong Typing)
  36. Q : - How to provide a replacement implementation during

    deployment?
  37. QUALIFIERS, ALTERNATIVES, PROGRAMMATICALLY LOOKUP Alternatives

  38. WHAT IS ALTERNATIVE BEAN? • Any bean with @Alternative is

    not considered for injection • Lets you package multiple beans that match injection type without ambiguity errors • In order to be considered for injection, it has to be activated in “beans.xml” • Provide a replacement implementation during deployment • You can apply the @Alternative annotation to two or more beans, then, based on your deployment, specify the bean you want to use in the “beans.xml” configuration file • Useful for providing mock objects for testing – mock objects are annotated with @Alternative
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  40. Q : - How to provide a replacement implementation during

    runtime?
  41. QUALIFIERS, ALTERNATIVES, PROGRAMMATICALLY LOOKUP Programmatically Lookup

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  43. SCOPE, & CONTEXT CDI Beans Scope

  44. Q : What the allowed scopes in CDI ?

  45. REQUEST – @REQUESTSCOPED • This scope describes a user’s interaction

    with a web application in a single HTTP request. • The instance of the @RequestScoped annotated bean has an HTTP request lifecycle.
  46. SESSION – @SESSIONSCOPED • This scope describes a user’s interaction

    with a web application across multiple HTTP requests.
  47. APPLICATION – @APPLICATIONSCOPED • In this case the state is

    shared across all users’ interactions with a web application. • The container provides the same instance of the @ApplicationScoped annotated bean to all client requests.
  48. DEPENDENT – @DEPENDENT PSEUDO-SCOPE • This pseudo-scope means that an

    object exists to serve exactly one client (bean) and has the same lifecycle as that client (bean). • This is the default scope for a bean which does not explicitly declare a scope type. • An instance of a dependent bean is never shared between different clients or different injection points. • It is strictly a dependent object of some other object. • It is instantiated when the object it belongs to is created, and destroyed when the object it belongs to is destroyed.
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  51. VIEW – @ VIEWSCOPED • @ViewScoped belongs to JSF specification

    • Retains the scope lifespan for current page view • If the controller navigates away to a different page view the bean is de-scoped • Therefore view-scope is great for form validation and rich AJAX request and response sequences!
  52. CONVERSATION – @CONVERSATIONSCOPED • A lifespan sits between a Http

    Request scope and Http Session scope • Maintains state for the unique interaction • Works for individual tab in web browsers • Better than @ViewScoped bean controllers • Application defined lifespan
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  54. SESSION & CONVERSATION SCOPED BEAN • A thing to notice

    is that beans must be serializable. • This is because the container passivates the HTTP session from time to time, so when the session is activated again the beans’ state must be retrieved.
  55. SINGLETON – @SINGLETON PSEUDO- SCOPE • This is a pseudo-scope.

    • It defines that a bean is once instantiated. • When a CDI managed bean is injected into another bean, the CDI container makes use of a proxy. • The proxy is the one to handle calls to the bean. • Though, @Singleton annotated beans don’t have a proxy object. • Clients hold a direct reference to the singleton instance.
  56. SINGLETON – @SINGLETON PSEUDO- SCOPE • So, what happens when

    a client is serialized ? • We must ensure that the singleton bean remains a singleton. • To do so there are a fiew ways, such as, have the singleton bean implement writeResolve() and readReplace() (as defined by the Java serialization specification), make sure the client keeps only a transient reference to the singleton bean, or give the client a reference of type Instance<X> where X is the bean type of the singleton bean.
  57. CONTEXTUAL SCOPE

  58. INTERCEPTORS, & DECORATORS Interceptors

  59. INTERCEPTORS • Interceptor functionality is defined in the Java Interceptors

    specification. • The Interceptors specification defines three kinds of interception points: • Business method interception, • Lifecycle callback interception, and • Timeout method interception (EJB only). • A business method interceptor applies to invocations of methods of the bean by clients of the bean • By default, all interceptors are disabled
  60. BUSINESS METHOD INTERCEPTOR • A business method interceptor applies to

    invocations of methods of the bean by clients of the bean
  61. LIFECYCLE CALLBACK INTERCEPTOR • A lifecycle callback interceptor applies to

    invocations of lifecycle callbacks by the container • An interceptor class may intercept both lifecycle callbacks and business methods
  62. TIMEOUT METHOD INTERCEPTOR • A timeout method interceptor applies to

    invocations of EJB timeout methods by the container
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  64. INTERCEPTORS, & DECORATORS Decorators

  65. WHAT IS A DECORATOR? • Decorators implement the Decorator design

    pattern • Allows implementation of an additional business logic for a bean • A Decorator decorates interfaces they implement • @Delegate is used to inject the original object • Original object business logic can be be invoked within the decorator • Decorators must be activated through “beans.xml”
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  68. Q : What is the deference between Interceptor and Decorators

    in CDI ?
  69. INTERCEPTORS VS DECORATORS • Interceptors and Decorators both geared towards

    cross-cutting logic. • Bypass traditional complexity associated with AOP by avoiding point-cuts. • Interceptors are designed for system-level crosscutting concerns very decoupled from business logic. • Decorators intended for concerns that should be compartmentalized but are still very close to business logic.
  70. EVENTS Events

  71. Q : What is Events ?

  72. CDI EVENT OBSERVER PATTERN • Completely decouple action (event producer)

    and reactions • (event consumers) • Qualifiers tune which event notifications are received • Define Event Class • Event producer fires an event • Event consumer observes event through @Observes
  73. EVENT • Event Producers • An event is fired by

    an injected javax.enterprise.event.Event object • Event Consumer (Event Observer) • The only thing event consumer has to do is to use @Observes <Event-class> annotation
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  75. CDI AND EJB When you still need EJB?

  76. Q : When you still need EJB ?

  77. WHEN YOU STILL NEED EJB ? … NOT YET ALIGNED!

    • Security • @RolesAllowed • @PermitAll • @DenyAll • Usable by • @Stateless • @Stateful • @Singleton
  78. WHEN YOU STILL NEED EJB ? … NOT YET ALIGNED!

    • Startup • @Startup • Eagerly creates the instance upon startup • Usable by • @Singleton
  79. WHEN YOU STILL NEED EJB ? … NOT YET ALIGNED!

    • Asynchronous • @Asynchronsous • Allows method calls to be asynchronous and return Future objects • Usable by • @Stateless • @Stateful • @Singleton
  80. WHEN YOU STILL NEED EJB ? … NOT YET ALIGNED!

    • Schedule • @Schedule • Effectively Cron -- schedule invocations by minute or date, etc. • Usable by • @Stateless • @Singleton • Not @Stateful
  81. WHEN YOU STILL NEED EJB ? … NOT YET ALIGNED!

    • Locking • @Lock(READ • @Lock(WRITE) • @AccessTimeout • Allows for synchronization of methods without complex code • Usable by • @Singleton • Not @Stateless • Not @Stateful
  82. WHEN YOU STILL NEED EJB ? … NOT YET ALIGNED!

    • MDBs • @MessageDriven • Connector-Driven Beans • Usable by • Not @Singleton • Not @Stateless • Not @Stateful
  83. CDI TAKEOVER • EJB adopts CDI (Java EE 6) •

    JSF adopts CDI (Java EE 7) • MVC adopts CDI (Java EE 8) • JAX-RS considers CDI (Java EE 8) • CDI moves to SE (Java EE 8)
  84. COMMON MISTAKES YOU WILL MAKE • Not putting a beans.xml

    in your app (Java EE 6) • No CDI for you! • Not understanding @Typed • Think @Local from EJB • Bites you when using @Produces • Not understanding what Dependent and NormalScope • Dependent == plain object • NormalScoped == proxied object • Bites you when creating custom scopes
  85. RESULT FOR EJB AFTER CDI ? • Java EE 7

    • Focus on realignment: @Transactional • • Java EE 8 • First spec round with no new EJB JSR • Realignment stalled • Awkward relationship
  86. CDI WRAP-UP Who did this now ! ! !

  87. CDI WRAP-UP • Basic dependency injection • @Inject, @Qualifier, @Alternative,

    • Instance, @All, @Any • Component naming • @Named • Context management • @Dependent, @RequestScoped, @SessionScoped, @ConversationScoped, @ApplicationScoped, @Scope
  88. CDI WRAP-UP • Custom Object Factories • @Produces, @Disposes, InjectionPoint

    • Lightweight Events • @Event, @Observes • Interceptors/Decorators • @Interceptor, @InterceptorBinding, @AroundInvoke, • InvocationContext • @Decorator, @Delegate
  89. BIGGEST BENEFITS OF CDI • Very active and open expert

    group • Fully extendable • Beans can be added at development, deployment, or even runtime • Fully Open Source • Spec is open source • All implementations are open source • Compliance test (TCK) suite is open source
  90. Q & A •https://about.me/ansgohar •http://ansgohar.blogspot.co.uk •https://twitter.com/ansgohar

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