EJB interview questions
- what are Container-Managed Transactional attributes ? view answer
- What's difference between httpsession and EJB session bean ? view answer
- What are the Differences between EJB 3.0 and EJB 2.1? view answer
- Q. what are Container-Managed Transactional arributes ? view answer
- What is the default transaction attribute for an EJB? view answer
- Difference between SessionBean remove() and EntityBean remove() method? view answer
- Why do we have a remove method in both EJBHome and EJBObject? view answer
- Is it possible to share an HttpSession between a JSP and EJB? What happens when I change a value in the HttpSession from inside an EJB? view answer
- What is the difference between a ?Coarse Grained? Entity Bean and a ?Fine Grained? Entity Bean? view answer
- What are the Interfaces need to create to implement Session Bean with Exmaple? view answer
- What are the parameters must follow for Session Bean ? view answer
- What are the callbacks method in Session Bean ? view answer
- What are the ways for a client application to get an EJB object?
- What is handle and why it is used in EJB? view answer
- What is an EJB Context? view answer
- Implement Local and Remote Interfaces in EJB? view answer
- How can I call one EJB from inside of another EJB?
- What is the difference between Message Driven Beans and Stateless Session beans? view answer
- What happens if remove( ) is never invoked on a session bean? view answer
- Can you control when passivation occurs?
- Can the primary key in the entity bean be a Java primitive type such as int?
- The EJB container implements the EJBHome and EJBObject classes. For every request from a unique client, does the container create a separate instance of the generated EJBHome and EJBObject classes?
- How can i maintain a user session between servlets and stateful session ejbs? view answer
- What's difference between Servlet/JSP session and EJB session view answer
- Is it possible to share an HttpSession between a JSP and EJB? What happens when I change a value in the HttpSession from inside an EJB?
- How to call any EJB from a servlet/JSP/Java Client? view answer
- What are transaction isolation levels in EJB?
- What are transaction attributes?
- What is bean managed transaction?
- Can Entity Beans have no create() methods?
- What are the callback methods in Entity beans?
- What is the difference between Container-Managed Persistent (CMP) bean and Bean-Managed Persistent(BMP) ?
- What are the methods of Entity Bean?
- What is Entity Bean?
- What is Session Bean?
- What are the different kinds of enterprise beans?
!!! EJB interview questions !!!
What is handle and why it is used in EJB?
The handle mechanism allows a client application to maintain a reference to an EJB object. A handle object may be obtained by calling the getHandle() method on the reference to an EJB object. The main interest is that the handle class implements java.io.serializable interface, which means that a handle may be serialized. This allows the client to store the handle, or to pass it to another process. The handle may then be deserialized and used to obtain the reference to the EJB object, by calling the getEJBObject() method.
Handles on session bean objects are valid until the session bean object exists, i.e. their life time is limited to that of the client. Handles on entity bean objects are valid during the complete life time of the entity bean object; this means that such handles may be used by different clients and stored for a long time; the EJB server holding the entity bean objects may be stopped and restarted, the handle will still be valid.
If we consider the entity bean object of the example above (a2), the way to obtain a handle on this object is the following (the handle class is defined in the javax.ejb package):
Handle h = a2.getHandle();The handle object may then be serialized and stored in a file:
ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("handlefile"));
Then, a client can read the handle, and retrieve the referenced object:
ObjectInputStream in = new ObjectInputStream(new FileInputStream("handlefile"));
Handle h = (Handle) in.readObject();
Account a = (Account)PortableRemoteObject.narrow(h.getEJBObject(),
The EJB Specification allows the client to obtain a handle for the home interface. This allows the client to store a reference to an entity bean's home interface in stable storage. The client code must use the javax.rmi.PortableRemoteObject.narrow(...) method to convert the result of the getEJBHome() method invoked on a handle to the home interface type
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