Kajigar Does not exists, Method Ready and Passivated states. Difference between start and run method in Thread A stateful session bean as per its name keeps associated client state in its instance variables. It was more difficult when EJB 2. It allows the ejb3 interview questions and answers to pass the test and brand themselves.
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Uploaded by. You are on page 1of 48 Search inside document 1. What is EJB? It enables rapid development of ission-critical application that are versatile, reusable and portable across middleware while protecting IT investment and preventing vendor lock-in.
What is session Facade? Session Facade is a design pattern to access the Entity bean through local interface than accessing directly. The ejbCreate methods is part of the beans lifecycle, so, the compiler will not return an error because there is no ejbCreate method.
However, the J2EE spec is explicit: the home interface of a Stateless Session Bean must have a single create method with no arguments, while the session bean class must contain exactly one ejbCreate method, also without arguments. Stateful Session Beans can have arguments more than one create method How to implement an entity bean which the PrimaryKey is an auto numeric field?
Object in the Deployment Descriptor. When defining the Primary Key for the Enterprise Bean, the Deployer using the Container Providers tools will typically add additional container-managed fields to the concrete subclass of the entity bean class.
In this case, the Container must generate the Primary Key value when the entity bean instance is created and before ejbPostCreate is invoked on the instance.
What is clustering? Clustering is grouping machines together to transparently provide enterprise services. Clustering is an essential piece to solving the needs for todays large websites. The client does not know the difference between approaching one server and approaching a cluster of servers. This has to be consider as passed-by-value, that means that its readonly in the EJB.
If my session bean with single method insert record into 2 entity beans, how can know that the process is done in same transaction the attributes for these beans are Required? If your session bean is using bean-managed transactions, you can ensure that the calls are handled in the same transaction by : javax. There is a common approach that is normally used and considered a good one.
You should start developing CMP beans, unless you require some kind of special bean, like multi-tables, that cannot be completely realized with a single bean. Then, when you realize that you need something more or that you would prefer handling the persistence performance issue are the most common reason , you can change the bean from a CMP to a BMP.
Whats different in Enterprise JavaBeans 1. The most significant changes are listed below: Entity bean support, both container- and bean-managed persistence, is required. The javax. Also the runAs declarations have been eliminated. Declarative isolation levels are no longer available.
The basic EJB roles have been expanded and redefined to better separate responsibilities involved in the development, deployment, and hosting of enterprise beans. What is Enterprise JavaBeans? EJB specifies how developers should build components that can be accessed remotely and how EJB vendors should support those components.
EJB components, called enterprise beans, automatically handle transactions, persistence, and authorization security, so that the developer can focus on the business logic. What is an enterprise bean? An enterprise bean is a server-side component defined in the Java technology which adheres to the Enterprise JavaBeans server-side component model.
A server-side component is business object that can be accessed remotely. Enterprise beans can be developed to represent business concepts like Employee, Order, Travel Agent, etc.
Enterprise beans can be assembled into applications that solve enterprise business problems. EJB has two basic types of enterprise beans: Session and Entity. Depending on the type of enterprise bean used, features like persistence, transactions, security, and multiple concurrent access can be managed automatically. Enterprise JavaBeans and JavaBeans are not the same thing; nor is one an extension of the other. They are both component models, based on Java, and created by Sun Microsystems, but their purpose and packages base types and interfaces are completely different.
JavaBeans The original JavaBeans specification is based on the java. Components built on the JavaBeans specification are intraprocess components that live in one address space and are typically used for Graphical User Interface GUI as visual widgets like buttons, tables, HTML viewers, etc. Components built on the EJB specification are intraprocess components that live in multiple address spaces as distributed object.
These components are used as transactional business objects that are accessed as remote objects. How does passivation work in stateful session beans?
Unlike entity beans and stateless session beans, stateful session bean are usually evicted from memory when they are passivated. EJb3 interview questions This is not true of all vendors but this view serves as good model for understanding the concepts of passivation in session beans. When a stateful bean experiences a lull in use between client invocations and transactions the container may choose to passivate the stateful bean instance.
To conserve resources the bean instance is evicted from memory dereferenced and garbage collected. When the EJB object receives a new client request, a new stateful instance is instantiated and associate with the EJB object to handle the request. Stateful beans maintain a conversational state, which must be preserved before the bean instance is evicted from memory.
To accomplish this, the container will write the conversational state of the bean instance to a secondary storage usually disk.
Only the non-transient serializable instance fields are preserved. When the bean is activated the new instance is populated with the preserved state.
SessionBean interface provides two callback methods that notify the bean instance it is about to passivated or was just activated. The ejbPassivate method notifies the bean instance that it is about have its conversational state written to disk and be evicted from memory. Within this method the bean developer can perform operations just prior to passivation like closing open resources.
The ejbActivate method is executed just after a new bean instance has been instantiated and populated with conversational state from disk. How does a client application create a transaction object? How you gain access to UserTransaction objects varies depending on the type of client. Enterprise JavaBeans provides two types of transaction management: Container-managed transactions.
As the name implies, the EJB container makes the decisions based on the deployment descriptors trans-attribute setting regarding how to bundle operations into transactions and then works with the transaction manager, which manages the transaction processing.
Bean-managed transactions. JMS clients can bundle several messages in a transaction simply by using a transactional sessiona UserTransaction object is not required. To create a transactional session, use either QueueConnection. Of course, for a servlet to obtain a UserTransaction object, there must be a JTS-capable server to deliver the object. Typically, the server provides the JNDI look-up name either directly or via a system or server property.
For example, with the WebLogic server, you would use a code segment similar to the following UserTransaction" ; ut. With J2EE implementations, you obtain the UserTransaction object with a code segment similar to the following If the environment provides the UserTransaction object via a system property, you would use a code segment similar to the following Do JTS implementations support nested transactions?
A JTS transaction manager must support flat transactions; support of nested transactions is optional. If a client begins a transaction, and within that transaction begins another transaction, the latter operation will throw a NotSupportedException if the JTS implementation does not support nested transactions.
Keep in mind that even if the JTS implementation supports nested transactions, this transaction manager-level support does not guarantee support for nested transactions in an application. For example, the EJB 1. Why would a client application use JTA transactions? In this scenario, the clients logic could required an all-or-nothing guarantee for the operations performed by the session beans; hence, the session bean usage could be bundled together with a JTA UserTransaction object. In the previous scenario, however, the client application developer should address the question of whether or not it would be better to encapsulate these operations in yet another session bean, and allow the session bean to handle the transactions via the EJB container.
In general, lightweight clients are easier to maintain than heavyweight clients. Also, EJB environments are ideally suited for transaction management.
If its necessary to engage in explicit transaction management, a session bean can be designed for bean-managed transactions and obtain a UserTransaction object via the EJBContext using the getUserTransaction method. It may also use JNDI directly, but its simpler to use this convenience method. Why would a session bean use bean-managed transactions?
In some situations, its necessary for a stateful session bean to selectively con trol which methods participate in transactions, and then take over the bundling of operations that form a logical unit of work. How does an enterprise bean that uses containermanaged transactions obtain a JTA UserTransaction object? It doesnt! By definition, container-managed transaction processing implies that the EJB container is responsible for transaction processing. The session bean has only limited control of transaction handling via the transaction attribute.
Yes, but with restrictions. By definition, a stateless session bean has no state; hence, each method invocation must be independent. The bean can be swapped out between method invocations.
Thus, a stateless session bean can obtain a UserTransaction object via the EJBContext using the getUserTransaction method, but it must start and finish each transaction within the scope of a method invocation. How do you configure a session bean for beanmanaged transactions?
You must set transaction-type in the deployment descriptor. It doesnt. Entity beans do not employ JTA transactions; that is, entity beans always employ declarative, container-managed transaction demarcation.
Entity beans, by definition, are somewhat tightly coupled via the EJB container and server to a datastore; hence, the EJB container is in the best position to manage transaction processing. Is it necessary for an entity bean to protect itself against concurrent access from multiple transactions? One of the motivations for using a distributed component architecture such as Enterprise JavaBeans is to free the business logic programmer from the burdens that arise in multiprogramming scenarios.
What are the constraints or drawbacks of container managed EJBs? With some implementations container-managed entity beans can only by mapped to one table, while other implemenations offer Multiple table mappings to a single bean.
EJB3 INTERVIEW QUESTIONS AND ANSWERS PDF
Uploaded by. You are on page 1of 48 Search inside document 1. What is EJB? It enables rapid development of ission-critical application that are versatile, reusable and portable across middleware while protecting IT investment and preventing vendor lock-in. What is session Facade?
EJB3 INTERVIEW QUESTIONS AND ANSWERS DOWNLOAD
Sabar What is difference between HashMap and Hashtable i What is Service locator ejb3 interview questions and answers pattern? This gives the double bonus of speeding up the initial load time for the application, as not quextions plug-ins are loaded straightaway; ensuring efficiency as only the plug-ins that are used are loaded at all. NEVER — Indicates if business method executes as part of transaction then an exception will be thrown. It is less resource intensive as compared to entity beans. Class level interceptor can be applied both by annotation or via xml ejb-jar.
EJB Interview Questions
There is an exception thrown when an entity beam is defined as non-re-entrant and numerous clients are connected to it concurrently to carry out a method. EJB — Interview Questions It consists of the business objects that call the client and deal with the session to access the client side session and their activities. We will see some of those in 10 interview questions on EJB. Ejb3 interview questions and answers are the ways through which the EJB control can be extended? Message bean Message beans provide are used to implement the messaging function in your application logic. User data can be saved to database via entity beans and later on can be retrived from the database in the entity bean. No you can not run EJB in web server like Tomcat.
EJB3 INTERVIEW QUESTIONS AND ANSWERS EPUB
You can expect to hear at least one - and likely more - of these questions during your next job interview. There is no better way to build self-confidence before your interview than to practice answering the questions you are most likely to be asked. While framing your answers to common questions is a good start, you should also practice answering them aloud, ideally in a role-playing scenario where a friend or family member can act the part of your interviewer. This will enable you to focus on your body language eye contact and posture as you respond to questions. Top 50 Popular Job Interview Questions Here are the 50 most frequently-asked questions that are posed in interviews.