EJB Questions

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2)What are the design goals of the Enterprise JavaBeansTM architecture?
The Enterprise JavaBeans specification defines a standard architecture for implementing the business logic of multi-tier applications as reusable components
In addition to Enterprise JavaBeans components, the architecture defines three other entities:servers,containers, and clients.
This architecture incorporates several design goals: Enterprise JavaBeans servers are designed to wrap around legacy systems to provide fundamental services for “containers and the components they contain”
Enterprise JavaBeans containers are designed to handle details of “component” life-cycle, transaction, and security management Component developers are free to focus on business logic, since containers provide services automatically by interceding in component method calls. A simple set of callback interfaces are all that a developer needs to implement to participate in container provided services. A client’s view of an Enterprise JavaBean remains the same regardless of the container it is deployed in. Any container in which an Enterprise JavaBean is deployed presents the same interfaces to the client. This extends to containers from different vendors, running against different servers and different databases, on diverse systems on a network. This client transparency ensures wide scalability for multi-tier applications.

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1)What is Enterprise JavaBeans?
a)EJB architecture is component architecture for the develeopment and deployment of component-based distributed business applications.EJB the widely adopted serverside component architecture for Java2 platform,Enterprise ediition(J2EE),versatile,reusable and portable across middleware.
2)Is Ejb a product?
a)No, Ejb is a specification,Enterprise JavBeans defines the EJB component architecture and the interfaces between the EJB enabled server and the component.
3)who are ejb product owners?
a)EJB is not a product it is a specification implemented by Sun with participation from many key vendors in the industry.Vendors like IBM,BEA,Sun and Oracle etc., are providing products that implement the EJB specification.
4)what are the main features in EJB?
a) EJB architecture is inherently transactional,distributed,portable,multiered and secure.
EJB components are serverside components written entirely in the java.
EJB components contain business logic only no system level programing.
System level services such as transactions,security,Life cycle,threading,persistence,etc are automatically managed by the EJB Component by the EJB server.
EJB architecture is wire-protocol neutral Any protocol can be utilized:HTTP,IIOP,DCOM etc.

5)what is current EJB version?
a)EJB2.0 is currently int he Expert Group phase of the JCP(Java Community process) specification development.
6)what are the key features to be included in EJB 2.0?
a)Integration with JMS.Message Driven bean has been introduced.
b)CMP for Entity bean was replaced with CMR.
c)Integration with Corba Interoperability protocol.

7)What about RMI/IIOP?
a)

8)How Client contact the Bean?
a)The Client view is provided through two interface—the home interface and the remote interface.These interfaces
are provided by classes constructed by the container when a bean is deployed, based on information provided by the bean
9)why doesn’t the client interact with an EnterPrise JavaBean directly?
a)To the client. there appears to be direct interaction with an EnterPrise JavaBean through the home and remote interface.The Container interacts between client and component,Completely concealing both bean instance and its own actions from the clients.
10)What methods are developers required to implement the Enterprise JavaBeans Architecture?
a)There are three categoriesof EJB methods.First, the bean implements methods to those in its home interface containeing methods,second abean implements business logic methods corresponding to those prvided by its remote interface.Finally a bean implements methods for interacting with the container.But these methods are not intended for client access, they are hidden by the container.
11)What are the basic types of Enterprise JavaBeans?
a)There are two types of Enterprise beans- session beans and entity beans represending different types of business logic abstactions.
Sesssion beans represent behaviors associated with client sessions,they are generally implemented to perform a sequence of tasks with in the context of a transaction.A Session bean is a logical extension of the client program, running process on the Clients behalf remotely on the server.
Entity beans reprsent specific data or collection of data, such as a row
in a relatiopnal database. Entity bean methods provided operations for action on the data represented by the bean.An entity bean is persistent,it servives as long as its data remains in the database.

12)How does a Client find and connect to a specific enterprise bean?
a)A client accesses an Enterprise JavaBean by looking up the class implemnting its home interface by name through JNDI.It then uses methods of the home interface to acquire access to an instance of the class implementing the remote interface.
13)How does a Client find and connect to a specific enterprise bean write the coding?
a) Context ct=new InitialContext();
HaiHome home=(HaiHome)ct.lookup(“hai”);
HaiRemote remote=home.create();

then remote.Business methods..
14)What general services does a container provide for an Enterprise JavaBean component?
a) A Container provides Enterprise JavaBeans Components with services of several types First it provides services for lifecycle management and instance pooling/cache Pooling(SFSB), including creation,activation,passvation, and destroy.Secod it interacts methods in a bean to enforce transction and security constraints.It enforce policies and restrictions on bean instances, such as reentrance rules security polices , and some others.

15)What classes and interfaces does a session bean developer define?
a)The Session bean developer defines the home and remote interfce that represent the client views of the bean.Developers also create a class that implements both SessionBean and SessionSynchronization interfaces , as well as methods corresponding to those in the beans home and remote interfaces.
16)what are main interfaces in EJB required ?
a)javax.ejb pacakage contains mainly SessionBean,EntityBean Interfaces
17)What are abstract methods in SessionBean ?
a)
public void setSessionContext(SessionContext ct)
public void ejbActivate()
public void ejbPassivate()
public void ejbRemove()

18)What are the abstract methods in EntityBean ?
a)
public void setEntityContext(EntityContext ct)
public void unSetEntityContext()
public void ejbActivate()
public void ejbPassivate()
public void ejbRemove()
public void ejbLoad()
public void ejbStore()

19)What are types in SessionBeans?
a) SessionBeans are mainly two types Stateless and Stateful

20)what are distinction between a stateless and stateful?
a) Stateless beans are beans that don’t maintain state across method calls.They are generally intended to perform individual operations automatically.Any instance of stateless bean can be used by any client at any timeStateful session beans maintain state within and between transactions Each Stateful session bean is associated with a specific client.Containers can automatically save and retrieve a beans state in the process of managing instance pools of stateful beans.
21)How do Stateful Session beans maintain consistency across transaction updates?
a) Stateful session beans maintain data consistency by updating their fields each time a transaction is committed.To keep informed of changes in transation status, a stateful session bean implements the SessionSynchronization interface.The Container then calls methods of this interface as it initiates and completes transactions involving the bean.
22)Can’t stateful session beans persistent?
a)Session beans are not designed to be persistent, whether stateful or stateless.A stateful session bean instance typically can’t survive system failures and other destructive events.
23) Is it possible to maintain persistence temporarly in stateful sessiionbeans?
a)yes,it is possible using Handle
24)What Classes and interfaces does an entity bean developer provide?
a) The Entity bean developer defines the home and remote interfaces that represent the cleint view of the bean.Developers also create a class that implements the EntityBean interface, as well as methods corresponding to those in the bean’s home and remote interface.
In addition to defininf create methods in the EJBHome interface, the entity bean develpoers must also implement finder methods.
25)What are types in EntityBeans?
a) EntityBeans are mainly two types BeanManaged and ContainerMAnaged
26)what’s a finder method?
a)A finder method provides a way to access an entity bean by its contents.
Finder methods are designed to be introspected and displayed by devleopment and deployment tools. The principal finder method that must be implement by all entity bean is finderByPrimaryKey.In addition to this method the developer must also implement a primaryKey class to provide each entity bean with a unique,serializable identity.

27)What is the difference between container-managed and beanmanaged persistence?
a)In bean managed persistenece, the bean is entirely responsible for storing and retriving its instance data.The EntityBean interface provides methods for the container to notify an instance when it needs to store or retrieve its data.
In container managed persistence, entity bean data is automatically maintained by the container using a mechanism of its choosing.

28)How is an entity bean created?
a)An entity bean can be created in two ways: by direct action of the client in which a create method is called on the bean’s home interfce or some other action that adds data to the database that the bean type represents.
29)How does the clent get a reference to an existing entitybean?
a)A client can get a reference to an existiing entity bean in several ways:
Receiving the bean as paramater in a method call
Looking the bean uo through a finder method of hte home interface
30) How does a container manages access from multiple transactions on an entiy bean?
a)Container can acquire an exclusive lock on the instances’s sate in the database and serializable acess from multiple transaction to this instance.

31)How do u determine whether two entity beans are the same?
a)By invoking the EntityBen.isIdentical method.This method should be implemented by the entitybean developer to determine when two reference are to the same object.

32)What are the transaction management benefits of the Enterprise JavaBeans architectur?
a)The Enterprise JavaBeans architecture provides automatic support for distributed transations in component based applications.Such distributed transactions can automatically update data in multiple databases.

33) Does Enterprise JavaBeans allow alternatives to container-manged transactions?
a)In addition to container-managed transactions, an Enterprise JavaBeans can participate in client-managed and bean-manged transactions.

34)What transaction attributes do Enterprise JavaBean containers support?
a) A container supports the following value for the transaction attribute of an Enterprise JavaBean.

TX_NOT_SUPPORTED
TX_BEAN_MANAGED
TX_REQUIRED
TX_SUPPORTS
TX_REQUIRES_NEW
TX_MANDATORY

35)Explaine the Transaction attributed?
a)A container supports the following value for the transaction attribute of an Enterprise JavaBean.
TX_NOT_SUPPORTED NOTSUPPORTED
The bean runs outside the context of a transaction.Existing transactions are suspended for the duration of method calls.
TX_BEAN_MANAGED NEVER
The bean demarks its own transactions boundaries through the JTA UserTransation interface.
TX_REQUIRED REQUIRED
Method calls require a transaction context.If one exists ,it will be used;if none exists,one will be created
TX_SUPPORTS SUPPORTS
Method calls use the current transaction context if one exists,but don’t create one if none exists.
TX_REQUIRES_NEW REQUIRESNEW
Continers create new transactions before each method call on the bean, and commit transacions before returing.
TX_MANDATORY
Method calls require a transacion context.If none exists, an exception is thrown.
36)What levels of transaction isolation does the Enterprise JavaBeans specification support?
a)The Enterprise JavaBeans specification defines four supported levels of transaction isolation:
TRANSACION_READ_COMMITED
TRANSACION_READ_UNCOMMITED
TRANSACION_REPETABLE_READ
TRANSACION_READ_SERIALIZABLE

EJB COMPONENTS DON’T SUPPORT THE JDBC ISOLATION LEVEL TRANSACTION_NONE

37)What is the relationship betwen Enterprise Java
Beans component architecture and XML technology?
a)EJB defines a standard for portable business logic and XML technology defines a standard for portable data.

38)How do you configure a session bean for bean-manged transactions?
a) By set transaction-type in the xml file.

39)How do you configure a session bean for bean-manged transactions?
a) By set transaction-attribute in the xml file or int he deployment descriptor.
41)Is is possible for an EJB client to marshall an object of class java.lang.Class to an EJB?
a)Technically yes, spec. compliant NO! “The enterprise bean must not attempt to query a class to

42)Is it possible to write two EJB’s that share the same Remote and Home interfaces, and have different bean classes?
if so, what are the advantages/disadvantages?
a)Sharing interfaces might be possible, but not trivial.
If you deploy with Sun Deployment Tool 1.2.1 you will get a
java.lang.ClassCastException: MyBean2EJB_EJBObjectImpl ...
43)Is it possible to specify multiple JNDI names when deploying an EJB?
a)No. To achieve this you have to deploy your EJB multiple times each specifying a different JNDI name. ..
44)What is the status of the UML-EJB Mapping Specification ?
a)It is currently > in the expert group stage, meaning that the CAll For > Experts (CAFE) was issued and replies were received. ...
45)Is it legal to have static initializer blocks in EJB?
a)Although technically it is legal,static initializer blocks are used to execute some piece of code before executing any constructor or method while instantiating ...
46)In CMP how can I define a finder method equivalent to a ‘SELECT * FROM BANKS ‘
Weblogic 5.1.0 - Define the following Finder syntax in your weblogic-ejb-jar.xml deployment descriptor.





47)Is it possible to access a CORBA object from a EJB? a)I am using VisiBroker 4.0 for my CORBA objects and J2EE 1.2.1 for my EJB. then These properties can be set on the commandline (using -Dorg. or using a file named orb.properties. Java:API:EJB, Java:API:CORBA Robert Castaneda ...

48)How can we interact with COM/DCOM components from a EJB component ?
a)A list of tools that integrate Java with the Microsoft platform is
available here. These tools can be used, as long as they stay within
the EJB specification requirements .

49)Is it possible to stop the execution of a method before completion
in a SessionBean?
a)Threads inside an EJB, One possible solution (that requires coding) would be to setting the transaction
50) What is a major difference SessionBean and EntityBean?
a) *SB’s state can be shared by only one client at a time. - persistence storage device is .ser file
*EB’s state can be shared by multiple clients, because as its persistence storage device is DB.
*Used to maintain client’s state persistent in the SB’s instance vars
51) What is the TX operational difference SessionBean and EntityBean?

a) SB may or may not be used for TX operational operations,even they are used for TXs bean developer itself responsible to update the bean values into DB.
b)EBs are specially designed for TX operations where bean develope is only responsible for updating bean values,
where the bean values were updated into DB by executing one additional funtion called ejbStore().
52)Who execute TX operation funtion?
a)Container for every regular intervals and interval time is the refreshMinutes property in JDBC Connection Pool Management.
53) What is the TX operational difference SessionBean and EntityBean?
a) SB may or may not be used for TX operational operations,
even they are used for TXs bean developer itself responsible to update the bean values into DB.
b)EBs are specially designed for TX operations
where bean develope is only responsible for updating bean values,
where the bean values were updated into DB by executing one additional funtion called ejbStore().

54)which beans are TX which are not?
a)
*SB are used for TX & Non Tx operations
*EBs are only used for TX operations.

55)what is the Entitybean flow control?
a)
1) Client obtains Home object reference.
2) Client to obtains Remote reference uses h.findByPrimaryKey(Object o)
Note: In place of Object any Object sub class type of reference can be passed as an argument.
3) The request of client received by HomeImpl class findByPrimaryKey(o)

b) It then checks the number of instance created in the container with the max beans in cache value,
if instances are less then container creates one new EJB instance
56)what are the Factors that influences ejbStore()?
a)
1) For every refereshMinutes interval
2) Before ejbPassivate()
3) Before ejbRemove()
57)In EBs the DB state is more consistent than SBs why?
a) by executing ejbLoad() & ejbStore()

58) In EBs the DB state is more consistent than SBs why?
a) by executing ejbLoad() & ejbStore()

59) what are the Factors that influences ejbLoad()?
a)
1) next to ejbFindByPrimaryKey()
2) after ejbActivate()
3) There is one property in DD file under called
600
Class c=Class.forName(“qualified classname”);
Object o=c.newInstance();
SBank sb=(simplebank.SBank)o;
sb.setEntitycContext(ec);
sb.ejbFindByPrimaryKey(i);
For the result of above funtion execution if bean doesn’t throws FinderException the container returns Remote object , if Exception found the same exception thrown back to the client.


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The Industry-Backed Server-Side Component Architecture
Since its introduction over two years ago, Enterprise JavaBeansTM technology has maintained unprecedented momentum among platform providers and enterprise development teams alike. That’s because the EJBTM server-side component model simplifies development of middleware components that are transactional, scalable, and portable. Enterprise JavaBeans servers reduce the complexity of developing middleware by providing automatic support for middleware services such as transactions, security, database connectivity, and more.
As an example, consider transaction management. In the past, developers have had to either write and maintain transaction management code, or rely on third-party transaction management systems, generally provided through proprietary, vendor specific APIs. In contrast, Enterprise JavaBeans technology enables components to participate in transactions—including distributed transactions—simply by specifying which objects and methods are transactional. The EJB server itself handles the underlying transaction management details, so developers can focus specifically on the business purpose of the objects and methods. And because EJB technology is based on the Java programming language, components can be deployed on any platform and operating system that supports the Enterprise JavaBeans standard, and any operting system.
The Enterprise JavaBeans technology model delivers benefits that address the most pressing concerns of enterprise development teams. These include reduced time to market for mission-critical applications, effortless scalability and portability, reduced reliance on hard to find developer skill sets, and an overall increase in developer productivity. EJB technology reduces the cost of developing enterprise scale applications, while protecting an organization’s existing investment in IT resources.

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1)Who is EJB technology for?

EJB technology benefits a number of audiences:
Enterprise customers that build and/or deploy EJB-based applications - gain development productivity, can choose from a wide selection of EJB servers, create business logic that runs everywhere and is architecture independent, all this while protecting their existing IT investment!
ISVs and SIs that develop EJB components or applications based on EJB components - Invest in business logic that is widely deployable, across any OS and middleware, don’t need to choose one vendor-specific server platform. Like enterprise customers they also benefit from productivity gains and architecture independence
The EJB specification itself is mostly targeted at the EJB server vendors - It is the blueprint that instructs these vendors on how to build an EJB server that EJB components can execute on successfully

2)What are the design goals of the Enterprise JavaBeansTM architecture?
The Enterprise JavaBeans specification defines a standard architecture for implementing the business logic of multi-tier applications as reusable components. In addition to Enterprise JavaBeans components, the architecture defines three other entities: servers, containers, and clients. This architecture incorporates several design goals:

Enterprise JavaBeans servers are designed to wrap around legacy systems to provide fundamental services for containers and the components they contain.
Enterprise JavaBeans containers are designed to handle details of component life-cycle, transaction, and security management. By interceding between clients and components at the method call level, containers can manage transactions that propagate across calls and components, and even across containers running on different servers and different machines. This mechanism simplifies development of both component and clients.
Component developers are free to focus on business logic, since containers provide services automatically by interceding in component method calls. A simple set of callback interfaces are all that a developer needs to implement to participate in container provided services.
A client’s view of an Enterprise JavaBean remains the same regardless of the container it is deployed in. Any container in which an Enterprise JavaBean is deployed presents the same interfaces to the client. This extends to containers from different vendors, running against different servers and different databases, on diverse systems on a network. This client transparency ensures wide scalability for multi-tier applications.
Along with container managed transactions, the Enterprise JavaBeans architecture enables component- and client-managed transactions. Containers can participate in component or client initiated transactions to enforce transaction rules across method call and component boundaries. Components can also specify transaction types by method, enabling them to mix transaction types within a single object.
A variety of Enterprise JavaBean attributes, including the default component transaction type, can be specified at either development or deployment time, and enforced through mechanisms built into the container architecture.
The Enterprise JavaBeans architecture is based on the Java programming language, so enterprise Beans take full advantage of the “write once, run anywhereTM” standard.
3)What’s the client view of an Enterprise JavaBeans component?
The client view is provided through two interfaces—the home interface and the remote interface. These interfaces are provided by classes constructed by the container when a bean is deployed, based on information provided by the bean. The home interface provides methods for creating a bean instance, while the remote interface provides the business logic methods for the component. By implementing these interfaces, the container can intercede in client operations on a bean, and offers the client a simplified view of the component.
4)Why doesn’t the client interact with an Enterprise JavaBean directly?
To the client, there appears to be direct interaction with an Enterprise Java Bean through the home and remote interfaces. However, Enterprise JavaBeans architecture is designed to enable clients and components to exist in different runtimes on different systems on a network. The container intercedes between client and component, completely concealing both the bean instance and its own actions from the clients.
5)What methods are developers required to implement the Enterprise JavaBeans architecture?
There are three categories of Enterprise JavaBeans methods. First, the bean implements methods corresponding to those in its home interface—methods largely for creating, locating and accessing instances of the bean. Second, a bean implements business logic methods corresponding to those provided by its remote interface. Finally, a bean implements methods for interacting with the container. Since these methods aren’t intended for client access, they are hidden by the container.
6)What specific services does a container provide for an entity bean?
As with session beans, the tools for a container generate additional classes for an entity bean at deployment time to implement the home and remote interfaces. These classes enable the container to intercede in all client calls on the same entity bean. The container also generates the serializable Handle class, providing a way to identify the entity bean within a specific life cycle. These classes can be implemented to mix in container-specific code for performing customized operations and functionality. In addition to these custom classes, each container provides a class to provide metadata to the client. Finally, where specified by a particular bean, a container manages persistence of selected fields of the entity bean.
7)What’s the difference between container-managed and bean-managed persistence?
In container-managed persistence, entity bean data is automatically maintained by the container using a mechanism of its choosing. For example, a container implemented on top of an RDBMS may manage persistence by storing each bean’s data as a row in a table. Or, the container may use Java programming language serialization for persistence. When a bean chooses to have its persistence container managed, it specifies which of its fields are to be retained.
In bean-managed persistence, the bean is entirely responsible for storing and retrieving its instance data. The EntityBean interface provides methods for the container to notify an instance when it needs to store or retrieve its data.
8)How is an entity bean created?
An entity bean can be created in two ways: by direct action of the client in which a create method is called on the bean’s home interface, or by some other action that adds data to the database that the bean type represents. In fact, in an environment with legacy data, entity objects may “exist” before an Enterprise JavaBean is even deployed.
9)How does the client get a reference to an existing entity bean?
A client can get a reference to an existing entity bean in several ways:
receiving the bean as a parameter in a method call
looking the bean up through a finder method of the home interface
obtaining the bean as a handle, a runtime specific identifier generated for a bean automatically by the container
10)How do you determine whether two entity beans are the same?
By invoking the EntityBean.isIdentical method. This method should be implemented by the entity bean developer to determine when two references are to the same object. Note that the equals and hashCode methods of Object are undefined for entity beans, since clients don’t directly access bean instances within a container.
11)How does a container manage access from multiple transactions on an entity bean?
Containers manage multiple transactions in one of two ways. First, the container can instantiate multiple instances of the bean and let the transaction management of the DBMS handle transaction processing issues. Or, the container can acquire an exclusive lock on the instance’s state in the database, and serialize access from multiple transactions to this instance.
12)How do enterprise beans handle concurrent and loopback calls on entity beans?
Concurrent calls in the same transaction context on the same Enterprise JavaBean component are illegal and may lead to unpredictable results. A bean can be marked as non-reentrant by its deployment descriptor. This allows the container to detect and prevent illegal concurrent calls from clients. On the other hand, some entity beans may require loopback calls: that is, calls where bean A is invoked, in turn invoking bean B, which then invokes a method call on bean A. This kind of concurrency is tricky and is best avoided.
TRANSACTION SUPPORT
14)What are the transaction management benefits of the Enterprise JavaBeans architecture?
The Enterprise JavaBeans architecture provides automatic support for distributed transactions in component based applications. Such distributed transactions can atomically update data in multiple databases, possibly even distributed across multiple sites. The Enterprise JavaBeans model shifts the complexities of managing these transactions from the application developer to the container provider.
Does Enterprise JavaBeans allow alternatives to container-managed transactions?
In addition to container-managed transactions, an Enterprise JavaBean can participate in client-managed and bean-managed transactions.
15)What transaction attributes do Enterprise JavaBean containers support?
A container supports the following values for the transaction attribute of an Enterprise JavaBean.
Not Supported
The bean runs outside the context of a transaction. Existing transactions are suspended for the duration of method calls.
Required
Method calls require a transaction context. If one exists, it will be used; if none exists, one will be created.
Supports
Method calls use the current transaction context if one exists, but don’t create one if none exists.
Requires New
Containers create new transactions before each method call on the bean, and commit transactions before returning.

Mandatory
Method calls require a transaction context. If none exists, an exception is thrown.
Never
Method calls require that no transaction context be present. If one exists, an exception is thrown.
16)How do bean-managed transactions work?
When a bean with bean managed transactions is invoked, the container suspends any current transaction in the client’s context. In its method implementation, the bean initiates the transaction through the JTA UserTransaction interface. In stateful beans, the container associates the bean instance with the same transaction context across subsequent method calls until the bean explicitly completes the transaction. However, stateless beans aren’t allowed to maintain transaction context across method calls. Each method invocation must complete any transaction it initiates.

ENTERPRISE JAVABEANS AND OTHER TECHNOLOGIES
17)What’s the relationship between Enterprise JavaBeans component architecture and CORBA?
The Enterprise JavaBeans specification is intended to support compliance with the range of CORBA standards, current and proposed.
A Bean’s remote and home interfaces are RMI compliant, and thus can interact with CORBA objects via RMI/IIOP, Sun and IBM’s forthcoming adaptation of RMI that conforms with the CORBA-standard IIOP protocol.
As a companion to the Enterprise JavaBeans specification, Sun Microsystems has defined a standard mapping from Enterprise Java Beans API to CORBA IDL.
JTA, the transaction API prescribed by the Enterprise JavaBeans specification for bean-managed transactions, is designed to layer easily over the OMG OTS transaction standard.
18)What’s the relationship between Enterprise JavaBeans component architecture and XML technology?
The two technologies are complementary: Enterprise JavaBeans defines a standard for portable business logic and XML technology defines a standard for portable data.
19)What’s the relationship between the Enterprise JavaBeans architecture and JTA?
The Enterprise JavaBeans architecture is intended to conceal transactional complexities from the component developer. Thus, developers and deployers writing to Enterprise JavaBeans architecture don’t need to access transaction management programmatically. However, in the case of bean- or client-managed transactions, the developer can call methods of JTA to initiate and complete transactions. JTA defines the Java programming language interfaces related to transaction management on the Java platform, conformant with the OMG/OTS standard.
The JTA UserTransaction interface is intended to be provided by containers to enable both bean-managed and client-managed transactions.
20)What’s the relationship between Enterprise JavaBeans and JDBC/SQLJ?
An entity bean can implement data persistence in one of two ways: bean-managed or container-managed. In the case of bean-managed persistence, the implementor of an entity bean stores and retrieves the information managed by the bean by means of direct database calls. For these, the bean can use either JDBC or SQLJ. The one tradeoff of this approach is that it makes it harder to adapt bean managed persistence to alternate data sources.
In the case of container-managed persistence, the container provider may implement access to the database using these APIs. The container provider can offer tools to map instance variable of an entity bean to calls to an underlying database. This approach makes it easier to use Beans with different databases.
Session beans also typically access the data they manage using JDBC or JSQL.

NEW FEATURES IN THE ENTERPRISE JAVABEANS 2.0 SPECIFICATION
21)How does the Enterprise JavaBeans 2.0 Specification support messaging?
The EJB 2.0 Specification defines JMS support through a new type of enterprise bean, the message-driven bean. A message-driven bean is invoked by the EJB container as the result of the arrival of a JMS message. To a client, the message-driven bean is a JMS consumer that implements some business logic on the server. Clients communicate with message-driven beans by sending messages to a JMS Destination (either a Queue or a Topic) for which the message-driven bean is a MessageListener.
Message driven beans are distinct from both Entity and Session beans. They have neither home nor remote interfaces. Instead, they implement the javax.jms.MessageListener interface.

22)What new features are provided to support container-managed persistence for Entity beans?
The EJB 2.0 Specification defines a new mechanism for modeling persistent data with Entity beans, and a new query language for Entity beans.
Features to support persistent data models include new abstract classes for both Entity beans and dependent objects. These classes can be implemented to define complex models for persistent data. EJB 2.0 also defines new deployment descriptor elements to define the^Mabstract schema supported by a bean. These allow the bean developer to specify the data model at development time, then allow a container’s deployment tools to automatically^Mgenerate the appropriate helper classes at deployment time. This provides additional platform-independence while supporting a richer representation of the data underlying an Entity bean.
In addition, EJB 2.0 defines the EJB QL, a query language that enables developers^Mto traverse the data model of Entity beans independently of the language used^Mby the underlying database. ^MEJB QL uses the abstract schema of entity beans, their dependent objects, and the^Mrelationships between these objects for its data model. The syntax of EJB QL is similar to that of SQL.
EJB QL enables Bean Providers to write two types of query methods:
Finder methods in the home interface to enable entity bean clients to select specific entity objects.
Select methods which allow a bean internal access to related data without exposing^Mthat data directly to the client.
23)How does EJB 2.0 improve support for interoperability between EJB containers and other J2EE products?
The EJB 2.0 public draft specification includes requirements on EJB container/server providers which enable interoperability for invocations on enterprise beans. These requirements enable communication with J2EE clients including JavaServer Pages, Servlets, Application Clients as well as with enterprise beans in other EJB containers. The goal of these features is to allow enterprise bean invocations to work even when client components and enterprise beans are deployed in J2EE products from different vendors. Support for interoperability between components includes transaction propagation, naming services and security services.
The interoperability mechanisms in EJB 2.0 are based on the IIOP protocol from the Object Management Group. The extensions supporting distributed transaction propagation, security (using SSL) and naming service access are all based on OMG standards. J2EE container products may also use vendor-specific protocols in addition to IIOP.

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Is is possible for an EJB client to marshall an object of class java.lang.Class to an EJB?
Technically yes, spec. compliant NO! - refer to section 18.1.2 of the EJB 1.1 specification (page 273). “The enterprise bean must not attempt to query a class to ...

Is it possible to write two EJB’s that share the same Remote and Home interfaces, and have different bean classes?
if so, what are the advantages/disadvantages?
Sharing interfaces might be possible, but not trivial.
If you deploy with Sun Deployment Tool 1.2.1 you will get a
java.lang.ClassCastException: MyBean2EJB_EJBObjectImpl ...

Is it possible to specify multiple JNDI names when deploying an EJB?
No. To achieve this you have to deploy your EJB multiple times each
specifying a different JNDI name. Java:API:EJB Andrea Pompili ...

What is the status of the UML-EJB Mapping Specification (JSR 26)?
Thank you for your interest in JSR-000026. It is currently > in the expert group stage, meaning that the CAll For > Experts (CAFE) was issued and replies were received. ...

Is it legal to have static initializer blocks in EJB?
Although technically it is legal, static initializer blocks are used to execute some piece of code before executing any constructor or method while instantiating ...

In CMP how can I define a finder method equivalent
to a ‘SELECT * FROM TABLE’? [RC - Please give reference
to the particular AppServer you are using]
Weblogic 5.1.0 - Define the following Finder syntax in your weblogic-ejb-jar.xml deployment descriptor. All ...

Is it possible to access a CORBA object from a EJB? I am using VisiBroker 4.0 for my CORBA objects and J2EE 1.2.1 for my EJB.
These properties can be set on the commandline (using -Dorg. or using a file named orb.properties. Java:API:EJB, Java:API:CORBA Robert Castaneda ...

How can we interact with COM/DCOM components from a EJB component ?
A list of tools that integrate Java with the Microsoft platform is
available here. These tools can be used, as long as they stay within
the EJB specification requirements ...
Is it possible to stop the execution of a method before completion in a SessionBean?
Threads inside an EJB, refer to section 18.1.2 of the EJB 1.1 specification. One possible solution (that requires coding) would be to set the transaction that the ...

Is it legal to have static initializer blocks in EJB?
Is it legal to have static initializer blocks in EJB? Java:API:EJB ravi srivatsav ...

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