Head First EJB
Passing the Sun Certified Business Component Developer Exam
Paperback Engels 2003 1e druk 9780596005719Samenvatting
What do Ford Financial, IBM, and Victoria's Secret have in common? Enterprise JavaBeans (EJB). As the industry standard for platform-independent reusable business components, EJB has just become Sun Microsystem's latest developer certification. Whether you want to be certifiable or just want to learn the technology inside and out, Head First EJB will get you there in the least painful way.
And with the greatest understanding. You'll learn not just what the technology *is*, but more importantly, *why* it is, and what it is and isn't good for. You'll learn tricks and tips for EJB development, along with tricks and tips for passing this latest, very challenging Sun Certified Business Component Developer (SCBCD) exam. You'll learn how to think like a server. You'll learn how to think like a bean.
And because this is a Head First book, you'll learn how to think about thinking. Co-author Kathy Sierra was one of Sun's first employees to teach brave, early adopter customers how to use EJB. She has the scars. But besides dragging you deep into EJB technology, Kathy and Bert will see you through your certification exam, if you decide to go for it. And nobody knows the certification like they do - they're co-developers of Sun's actual exam! As the second book in the Head First series, Head First EJB follows up the number one best-selling Java book in the US, Head First Java.
Find out why reviewers are calling it a revolution in learning tough technical topics, and why Sun Chairman and CEO Scott McNealy says, "Java technology is everywhere...if you develop software and haven't learned Java, it's definitely time to dive in "Head First." And with Head First book, you don't even have to feel guilty about having fun while you're learning; it's all part of the learning theory. If the latest research in cognitive science, education, and neurobiology suggested that boring, dry, and excruciatingly painful was the best way to learn, we'd have done it. Thankfully, it's been shown that your brain has a sense of style, a sense of humour, and a darn good sense of what it likes and dislikes.
In Head First EJB, you'll learn all about:
- Component-based and role-based development
- The architecture of EJB, distributed programming with RMI
- Developing and Deploying an EJB application
- The Client View of a Session and Entity bean
- The Session Bean Lifecycle and Component Contract
- The Entity bean Lifecycle and Component Contract
- Container-managed Persistence (CMP)
- Container-managed Relationships (CMR)
- EJB-QL
- Transactions
- Security
- EJB Exceptions
- The Deployment Descriptor
- The Enterprise Bean Environment in JNDI
- Programming Restrictions and Portability
The book includes over 200 mock exam questions that match the tone, style, difficulty, and topics on the real SCBCD exam. See why Kathy and Bert are responsible for thousands of successful exam-passers- "The Sun certification exam was certainly no walk in the park, but Kathy's material allowed me to not only pass the exam, but Ace it!" --Mary Whetsel, Sr. Technology Specialist, Application Strategy and Integration, The St. Paul Companies "Kathy Sierra and Bert Bates are two of the few people in the world who can make complicated things seem damn simple, and as if that isn't enough, they can make boring things seem interesting." --Paul Wheaton, The Trail Boss, javaranch.com "Who better to write a Java study guide than Kathy Sierra, reigning queen of Java instruction? Kathy Sierra has done it again. Here is a study guide that almost guarantees you a certification!" --James Cubetta, Systems Engineer, SGI
Specificaties
Lezersrecensies
Inhoudsopgave
What is EJB all about?
What does EJB really give me?
No more vendor lock-in!
How does it all work?
Behind the scenes...
Beans come in three flavors
Session beans can be stateless or stateful
Example: The Advice Guy bean
Five things you do to build a bean:
EJB Roles and Responsibilities
Tutorial:
Organize your project directory
Compile the two interfaces and the bean class
Start the server
You’ll see something like this
Start deploytool
you’ll see something like this
Make a new Application
Name and save the new application
What you’ll see after you create and name the application
Now let’s make the new enterprise bean (the ejb-jar and the DD)
Now we’re in the really cool New Enterprise Bean Wizard
Create the new ejb-jar
Add the three class files (including their package directory) to the JAR
Confirm that you added ONLY the package directory and the class files
Make it a Stateless Session bean
Tell it which of the three class files in the JAR is the actual BEAN class
Tell it which is the Home interface, and which is the Component interface
Verify everything on this screen!
You’re done, click Finish
Meanwhile back on the main deploytool screen...
Run your bean through the deploytool verifier
Close your eyes and click OK
Whew! No failed tests
Time to Deploy
Make it Return a Client Jar
Give it a name, so clients can look it Up
Watch the progress bars go up, then celebrate
Now you’ll see the AdviceApp inside the server
Now all we need is a client...
Organizing your project directory for the client
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Chapter 2 Architectural Overview: EJB Architecture
You remember this picture...
Making a remote method call
There’s a “helper” on the server as well...
What about arguments and return values?
What really gets passed when you pass an object to a remote method?
Passing a Remote object through a remote method call
What must the Remote object and the stub have in common?
The client calls business methods on the stub through the Remote business interface
How EJB uses RMI
The Remote object is not the bean, it’s the bean’s bodyguard—the EJBObject
The Component interface
Who writes the class that really DOES implement the component interface? In other words, who makes the EJBObject class?
Who creates what?
The bean Home
Architectural overview: Entity beans
Architectural overview: Creating a Stateful Session bean
Architectural overview: Creating a Stateless Session bean
Who creates the stateless session bean, and when?
Stateless session beans are more scalable
Architectural overview: Message-driven beans
Chapter 3 The Client View: Exposing Yourself
What the client really wants
It all starts with the home interface
How a client uses a session bean: create, use, and remove
But first, we have to get a home interface reference
Let’s take another look at the complete client code
Just when you thought a simple cast would be enough...
But NO. You have to narrow the object as well!
OK, I’ll bite. Why can’t you just do a plain old cast?
PortableRemoteObject.narrow()
Writing the Remote home interface for a session bean
Remote home interface examples for session beans
But enough about the home... let’s talk about the EJB object. The component interface. The thing you REALLY want.
Imagine what else you might want to do with your EJB object reference...
Thankfully, we’ve got handles
isIdentical?
A bean’s client interfaces can be local
Which methods make sense for the local client interfaces?
When you think handle, think Remote
Who needs EJBMetaData when you’ve got reflection?
Do you need isIdentical() when there’s equals()?
Why so many remove methods?
Comparing Remote vs. Local interfaces
Writing the local client interfaces
You can have both a Remote and local client view for a bean, but you probably won’t.
Exceptions in client interfaces: what the client might get
Local client code
What has to change inside the bean class?
Arguments to Remote vs. local methods
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Chapter 4 Session Bean Lifecycle: Being a Session Bean
Exploring the session bean lifecycle
You remember how it all works, right?
There’s obviously more to the bean’s lifecycle than just creation and business methods...
Container Callbacks, for the special moments in a bean’s life...
Container Callbacks come from TWO places
Implementing the container callbacks
We have to look at the transitions
Bean Creation: when an object becomes a bean
Bean things you can do during creation
Bean Use: what happens AFTER creation...
Bean things you can do within business methods
Passivation: a stateful bean’s chance at scalability...
Your job for passivation: make your state passivatable!
Bean things you can do in ejbActivate() and ejbPassivate()
Bean Removal: when beans die
Complaints about bean removal
Bean things you can do in ejbRemove()
Implementing the AdviceBean as a stateFUL bean
AdviceStatefulBean code
AdviceStatefulBean CLIENT code
Deploying a stateful bean
Compared to stateful beans, stateless beans have a simple life
Bean things you can do from stateless bean methods
Writing a Session Bean: your job as Bean Provider
SessionContext
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Chapter 5 Entity Bean Intro: Entities are Persistent
What’s an entity bean?
Entities vs. Entity Beans
Entity beans from the client’s point of view
A very simple Customer entity bean
An entity bean’s client view
Entity bean Remote component interface
Entity bean Remote component interface
Entity bean Remote home interface
What does the client really want from an entity bean home?
Entity bean Remote home interface
When finders have a dark side...
Home business methods to the rescue
Session bean create() vs. entity bean create()
Session bean remove() vs. entity bean remove()
Entity/bean/instance death
Entity bean client view
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Chapter 6 Bean/Entity Synchronization: Being an Entity Bean
The real power of entity beans is synchronization
The only question is WHO does the work when it’s time to synchronize
Container-managed vs. bean-managed persistence
A brief history on the evolution of CMP 2.0
The EntityBean interface adds three new container callbacks (including two just for synchronization)
Even the methods that are the same, don’t behave the same
But wait... there’s more! Entity beans have new home container callbacks, too
Writing a CMP entity bean: make it abstract
You put three kinds of things in your bean class:
PLUS... (ok, that’s four things...)
Virtual fields are NOT instance variables!
Complete code for the CustomerBeanCMP class
So how DID the client get a reference to the EJB object for #28?
Bean things you can do during entity construction:
Object identity: the primary key
Bean things you can do during entity creation:
Bean things you can do in home business methods
Bean things you can do during activation and loading
Bean things you can do during passivation and storing
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Chapter 7 Entity Relationships: When Beans Relate
Beanifying your movie database
But we don’t want to think in TABLES We want to think in CLASSES
We need relationships between the Movie bean and the Director bean
Why should the Director be a bean? Why can’t it just be data?
Relationships and multiplicity
Multiplicity in Bean Classes
Multiplicity affects return type!
Defining virtual fields for persistent data fields and relationship fields
Defining your “abstract persistence schema” (virtual fields aren’t enough)
Persistent CMP fields in the DD
Using relationships in your code
Defining relationships in your abstract persistence schema (in the DD)
Mapping from abstract schema to a real database
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Chapter 8 Message-Driven Beans: Getting the Message
Imagine this scenario...
Too bad these guys aren’t message-driven beans
Message-driven bean class
Writing a message-driven bean: your job as Bean Provider
Notice something missing from the code?
Topics and Queues
Only ONE bean per pool gets a copy of a topic message
With a queue, only one bean gets the message. Period.
MessageDrivenContext
MessageDrivenContext
What if something goes wrong?
Message acknowledgement
That’s all well and good, but let’s go back and see how our earlier scenario ended...
Think about it.
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Chapter 9 EJB Transactions: The Atomic Age
The ACID test
Distributed transactions: two-phase commit
How it works in EJB
Some transactions don’t propagate
How do I make (or get) a transaction?
Transaction-related methods are in two interfaces
Making a BMT transaction
Call stack of the checkOut() method
Things you must NOT do with BMT
What does it mean to suspend a transaction?
The UserTransaction interface
setRollbackOnly()
setRollbackOnly() lives in TWO interfaces
getRollbackOnly()
BMT beans use getStatus() instead of getRollbackOnly()
BMT can be a really BAD idea. BMT hurts bean reuse
Container-managed transactions
How attributes work
Transaction attributes that require a transaction
Transaction attributes that do not require a transaction
These are the methods you MUST mark with an attribute (for a CMT bean)
“Unspecified Transaction Context”
Burn these in
Marking transactions in the DD
DD example for CMT
More DD examples for CMT
Summary of Bean-managed demarcation
Entity beans have ejbLoad() to stay synchronized, even if the transaction rolls back.
Session Synchronization
SessionSynchronization “special moments”
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Chapter 10 Exceptions in EJB: When beans go bad
What can go wrong?
Remember, Java exceptions can be checked or unchecked
It’s all about expectations...
In EJB, exceptions come in two flavors: application and system
With an Application Exception, the Container will...
With a System Exception, the Container will...
Warning! RemoteException is checked, but not expected!
RemoteException goes to remote clients EJBException goes to local clients
Bean Provider’s responsibilities
The Container’s responsibilities
The five standard EJB application exceptions
The five standard application exceptions from the client’s point of view
Common system exceptions
Common system exceptions
Scenarios: what do you think happens?
Scenario Summary
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Chapter 11 Security in EJB: Protect Your Secrets
Imagine you’re writing a payroll application...
What can you do?
How to do security in EJB
The Application Assembler’s job: access control
Defining the roles
Defining the roles... a better way
Defining the method permissions
Defining the method permissions
Method permissions interact with one another as a union!
Watch out for <unchecked/>
The Deployer’s job: mapping actual humans to abstract roles
Principals and Roles, Users and Groups
Class-level vs. instance-level security
Using programmatic security to custom-tailor a method
The problem with isCallerInRole()...
Map declarative security roles to the programmer’s hard-coded (fake) roles
Use <run-as> security identity to pretend someone else is calling...
Security context propagation with <run-as>
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Chapter 12 A Bean’s Environment: The Joy of Deployment
A bean’s special place- java:comp/env
But it’s not per bean instance... It’s per bean home
It’s simple... if the programmer puts a made-up JNDI name in code, he has to announce that to the deployer in the DD.
Bean Provider and Application Assembler responsibility for the Deployment Descriptor
Deployer responsibility for the Deployment Descriptor
Remembering who does what
Now let’s look at the bean’s runtime environment
Which APIs does EJB 2.0 guarantee?
What MUST be in an ejb-jar?
Structure of an ejb-jar
Programming restrictions
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Appendix A: Final Mock Exam
Coffee Cram
Coffee Cram: Master Mock Exam
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This isn’t goodbye
Cover Rough Drafts for the series
Appendix B: Interface summary
Rubrieken
- advisering
- algemeen management
- coaching en trainen
- communicatie en media
- economie
- financieel management
- inkoop en logistiek
- internet en social media
- it-management / ict
- juridisch
- leiderschap
- marketing
- mens en maatschappij
- non-profit
- ondernemen
- organisatiekunde
- personal finance
- personeelsmanagement
- persoonlijke effectiviteit
- projectmanagement
- psychologie
- reclame en verkoop
- strategisch management
- verandermanagement
- werk en loopbaan