ServiceNow Most Frequently Asked Latest Advanced Java Interview Questions Answers
What Is Bean Managed Transaction?
If a developer doesn't want a Container to manage transactions, it's possible to implement all database operations manually by writing the appropriate JDBC code. This often leads to productivity increase, but it makes an Entity Bean incompatible with some databases and it enlarges the amount of code to be written. All transaction management is explicitly performed by a developer.
What Are Transaction Attributes?
The transaction attribute specifies how the Container must manage transactions for a method when a client invokes the method via the enterprise bean’s home or component interface or when the method is invoked as the result of the arrival of a JMS message. (Sun's EJB Specification) Below is a list of transactional attributes
1. NotSupported - transaction context is unspecified.
2. Required - bean's method invocation is made within a transactional context. If a client is not associated with a transaction, a new transaction is invoked automatically.
3. Supports - if a transactional context exists, a Container acts like the transaction attribute is Required, else - like NotSupported.
4. RequiresNew - a method is invoked in a new transaction context.
5. Mandatory - if a transactional context exists, a Container acts like the transaction attribute is Required, else it throws a javax.ejb.TransactionRequiredException.
6. Never - a method executes only if no transaction context is specified.
What Are Transaction Isolation Levels In Ejb?
1. Transaction_read_uncommitted- Allows a method to read uncommitted data from a DB(fast but not wise).
2. Transaction_read_committed- Guarantees that the data you are getting has been committed.
3. Transaction_repeatable_read - Guarantees that all reads of the database will be the same during the transaction (good for read and update operations).
4. Transaction_serializable- All the transactions for resource are performed serial.
How Ejb Invocation Happens?
Retrieve Home Object reference from Naming Service via JNDI.
Return Home Object reference to the client.
Create a new EJB Object through Home Object interface.
Create EJB Object from the Ejb Object
Return EJB Object reference to the client.
Invoke business method using EJB Object reference.
Delegate request to Bean (Enterprise Bean).
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?
You can pass the HttpSession as parameter to an EJB method, only if all objects in session are serializable.This has to be consider as passed-by-value", that means that its read-only in the EJB. If anything is altered from inside the EJB, it wont be reflected back to the HttpSession of the Servlet Container.The pass-by-reference can be used between EJBs Remote Interfaces, as they are remote references. While it IS possible to pass an HttpSession as a parameter to an EJB object, it is considered to be bad practice in terms of object oriented design. This is because you are creating an unnecessary coupling between back-end objects (ejbs) and front-end objects (HttpSession). Create a higher-level of abstraction for your ejbs api. Rather than passing the whole, fat, HttpSession (which carries with it a bunch of http semantics), create a class that acts as a value object (or structure) that holds all the data you need to pass back and forth between front-end/back-end. Consider the case where your ejb needs to support a non-http-based client. This higher level of abstraction will be flexible enough to support it.
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?
The EJB container maintains an instance pool. The container uses these instances for the EJB Home reference irrespective of the client request. while refering the EJB Object classes the container creates a separate instance for each client request. The instance pool maintainence is up to the implementation of the container. If the container provides one, it is available otherwise it is not mandatory for the provider to implement it. Having said that, yes most of the container providers implement the pooling functionality to increase the performance of the application server. The way it is implemented is again up to the implementer.
Can The Primary Key In The Entity Bean Be A Java Primitive Type Such As Int?
The primary key can't be a primitive type--use the primitive wrapper classes, instead. For example, you can use java.lang.Integer as the primary key class, but not int (it has to be a class, not a primitive)
Can You Control When Passivation Occurs?
The developer, according to the specification, cannot directly control when passivation occurs. Although for Stateful Session Beans, the container cannot passivate an instance that is inside a transaction. So using transactions can be a a strategy to control passivation.
The ejbPassivate() method is called during passivation, so the developer has control over what to do during this exercise and can implement the require optimized logic.
Some EJB containers, such as BEA WebLogic, provide the ability to tune the container to minimize passivation calls.
Taken from the WebLogic 6.0 DTD -"The passivation-strategy can be either "default" or "transaction". With the default setting the container will attempt to keep a working set of beans in the cache. With the "transaction" setting, the container will passivate the bean after every transaction (or method call for a non-transactional invocation).
What Is The Advantage Of Using Entity Bean For Database Operations, Over Directly Using Jdbc Api To Do Database Operations? When Would I Use One Over The Other?
Entity Beans actually represents the data in a database. It is not that Entity Beans replaces JDBC API. There are two types of Entity Beans Container Managed and Bean Mananged. In Container Managed Entity Bean - Whenever the instance of the bean is created the container automatically retrieves the data from the DB/Persistance storage and assigns to the object variables in bean for user to manipulate or use them. For this the developer needs to map the fields in the database to the variables in deployment descriptor files (which varies for each vendor).
In the Bean Managed Entity Bean - The developer has to specifically make connection, retrive values, assign them to the objects in the ejbLoad() which will be called by the container when it instatiates a bean object. Similarly in the ejbStore() the container saves the object values back the the persistance storage. ejbLoad and ejbStore are callback methods and can be only invoked by the container. Apart from this, when you use Entity beans you dont need to worry about database transaction handling, database connection pooling etc. which are taken care by the ejb container. But in case of JDBC you have to explicitly do the above features. what suresh told is exactly perfect. ofcourse, this comes under the database transations, but i want to add this. the great thing about the entity beans of container managed, whenever the connection is failed during the transaction processing, the database consistancy is mantained automatically. the container writes the data stored at persistant storage of the entity beans to the database again to provide the database consistancy. where as in jdbc api, we, developers has to do manually.
What Is Ejb Ql?
EJB QL is a Query Language provided for navigation across a network of enterprise beans and dependent objects defined by means of container managed persistence. EJB QL is introduced in the EJB 2.0 specification. The EJB QL query language defines finder methods for entity beans with container managed persistenceand is portable across containers and persistence managers. EJB QL is used for queries of two types of finder methods: Finder methods that are defined in the home interface of an entity bean and which return entity objects. Select methods, which are not exposed to the client, but which are used by the Bean Provider to select persistent values that are maintained by the Persistence Manager or to select entity objects that are related to the entity bean on which the query is defined.
Brief Description About Local Interfaces?
EEJB was originally designed around remote invocation using the Java Remote Method Invocation (RMI) mechanism, and later extended to support to standard CORBA transport for these calls using RMI/IIOP. This design allowed for maximum flexibility in developing applications without consideration for the deployment scenario, and was a strong feature in support of a goal of component reuse in J2EE.
Many developers are using EJBs locally -- that is, some or all of their EJB calls are between beans in a single container.
With this feedback in mind, the EJB 2.0 expert group has created a local interface mechanism. The local interface may be defined for a bean during development, to allow streamlined calls to the bean if a caller is in the same container. This does not involve the overhead involved with RMI like marshalling etc. This facility will thus improve the performance of applications in which co-location is planned.
Local interfaces also provide the foundation for container-managed relationships among entity beans with container-managed persistence.
What Are The Special Design Care That Must Be Taken When You Work With Local Interfaces?
EIt is important to understand that the calling semantics of local interfaces are different from those of remote interfaces. For example, remote interfaces pass parameters using call-by-value semantics, while local interfaces use call-by-reference.
This means that in order to use local interfaces safely, application developers need to carefully consider potential deployment scenarios up front, then decide which interfaces can be local and which remote, and finally, develop the application code with these choices in mind.
While EJB 2.0 local interfaces are extremely useful in some situations, the long-term costs of these choices, especially when changing requirements and component reuse are taken into account, need to be factored into the design decision.
What Happens If Remove( ) Is Never Invoked On A Session Bean?
In case of a stateless session bean it may not matter if we call or not as in both cases nothing is done. The number of beans in cache is managed by the container.
In case of stateful session bean, the bean may be kept in cache till either the session times out, in which case the bean is removed or when there is a requirement for memory in which case the data is cached and the bean is sent to free pool.
How Can I Call One Ejb From Inside Of Another Ejb?
EJBs can be clients of other EJBs. It just works. Use JNDI to locate the Home Interface of the other bean, then acquire an instance reference, and so forth.
What Is An Ejb Context?
EJBContext is an interface that is implemented by the container, and it is also a part of the bean-container contract. Entity beans use a subclass of EJBContext called EntityContext. Session beans use a subclass called SessionContext. These EJBContext objects provide the bean class with information about its container, the client using the bean and the bean itself. They also provide other functions. See the API docs and the spec for more details.
What Are The Two Important Tcp Socket Classes?
Socket and ServerSocket.
ServerSocket is used for normal two-way socket communication.
Socket class allows us to read and write through the sockets. getInputStream() and getOutputStream() are the two methods available in Socket class.
What Technologies Are Included In J2ee?
The main technologies in J2EE are: Enterprise JavaBeansTM (EJBsTM), JavaServer PagesTM (JSPsTM), Java Servlets, the Java Naming and Directory InterfaceTM (JNDITM), the Java Transaction API (JTA), CORBA, and the JDBCTM data access API.
What Is The Difference Between Ejb And Java Beans?
EJB is a specification for J2EE server, not a product; Java beans may be a graphical component in IDE.
What Is Ejb Role In J2ee?
EJB technology is the core of J2EE. It enables developers to write reusable and portable server-side business logic for the J2EE platform.
Tell Me Something About Local Interfaces.
EJB was originally designed around remote invocation using the Java Remote Method Invocation (RMI) mechanism, and later extended to support to standard CORBA transport for these calls using RMI/IIOP. This design allowed for maximum flexibility in developing applications without consideration for the deployment scenario, and was a strong feature in support of a goal of component reuse in J2EE. Many developers are using EJBs locally, that is, some or all of their EJB calls are between beans in a single container. With this feedback in mind, the EJB 2.0 expert group has created a local interface mechanism. The local interface may be defined for a bean during development, to allow streamlined calls to the bean if a caller is in the same container. This does not involve the overhead involved with RMI like marshalling etc. This facility will thus improve the performance of applications in which co-location is planned. Local interfaces also provide the foundation for container-managed relationships among entity beans with container-managed persistence.
What Is Enterprise Javabeans (ejb) Container?
It manages the execution of enterprise beans for J2EE applications. Enterprise beans and their container run on the J2EE server.
What Is In-memory Replication?
The process by which the contents in the memory of one physical m/c are replicated in all the m/c in the cluster is called in-memory replication.
What Is Ripple Effect?
The process of propagating the changes in the properties of a server group during runtime to all the associated clones is called Ripple Effect.
What Is A Clone?
The copies of a server group are called Clones. But unlike a Server Group Clones are associated with a node and are real server process running in that node.
What Are The Types Of Scaling?
There are two types of scaling: Vertical Scaling and Horizontal Scaling.
Vertical Scaling - When multiple server clones of an application server are defined on the same physical m/c, it is called Vertical Scaling. The objective is to use the processing power of that m/c more efficiently.
Horizontal Scaling - When Clones of an application server are defined on multiple physical m/c, it is called Horizontal Scaling. The objective is to use more than one less powerful m/c more efficiently.
What Is A Server Group?
A server group is a template of an Application Server(and its contents) i.e, it is a logical representation of the application server. It has the same structure and attributes as the real Application Server, but it is not associated with any node, and does not correspond to any real server process running on any node.
What Is The New Basic Requirement For A Cmp Entity Bean Class In 2.0 From That Of Ejb 1.1?
It must be abstract class. The container extends it and implements methods which are required for managing the relationships.
What's New In The Ejb 2.0 Specification?
Following are some of the main features supported in EJB 2.0
1. Integration of EJB with JMS,
2. Message Driven Beans,
3. Implement additional Business methods in Home interface which are not specific for bean instance, EJB QL.
How Can I Access Ejb From Asp?
We can use the Java 2 Platform, Enterprise Edition Client Access Services (J2EETM CAS) COM Bridge 1.0, currently downloadable from Sun.
What Is The Relationship Between Local Interfaces And Container-managed Relationships?
Entity beans that have container-managed relationships with other entity beans, must be accessed in the same local scope as those related beans, and therefore typically provide a local client view. In order to be the target of a container-managed relationship, an entity bean with container-managed persistence must provide a local interface.
What Is Ejbdoclet?
EJBDoclet is an open source JavaDoc doclet that generates a lot of the EJB related source files from custom JavaDoc comments tags embedded in the EJB source file.
What Is The Difference Between Session And Entity Beans?
An entity bean represents persistent global data from the database; a session bean represents transient user-specific data that will die when the user disconnects (ends his session). Generally, the session beans implement business methods (e.g. Bank.transferFunds) that call entity beans (e.g. Account.deposit, Account.withdraw)
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 a class. Static initializer blocks are also typically used to initialize static fields - which may be illegal in EJB if they are read/write - In EJB this can be achieved by including the code in either the ejbCreate(), setSessionContext() or setEntityContext() methods.
What Are Local Interfaces? Describe.
EJB was originally designed around remote invocation using the Java Remote Method Invocation (RMI) mechanism, and later extended to support to standard CORBA transport for these calls using RMI/IIOP. This design allowed for maximum flexibility in developing applications without consideration for the deployment scenario, and was a strong feature in support of a goal of component reuse in J2EE. Many developers are using EJBs locally, that is, some or all of their EJB calls are between beans in a single container. With this feedback in mind, the EJB 2.0 expert group has created a local interface mechanism. The local interface may be defined for a bean during development, to allow streamlined calls to the bean if a caller is in the same container. This does not involve the overhead involved with RMI like marshalling etc. This facility will thus improve the performance of applications in which co-location is planned. Local interfaces also provide the foundation for container-managed relationships among entity beans with container-managed persistence.
What Is Difference Between Ejb 1.1 And Ejb 2.0?
The bulk of the changes in EJB 2.0 are found in the definition of a new CMP component model. It’s radically different from the old CMP model because it introduces an entirely new participant, the persistence manager, and a completely new way of defining container-managed fields, as well as relationships with other beans and dependent objects.
What Is The Difference Between Ejbcreate() And Ejbpostcreate?
The purpose of ejbPostCreate() is to perform clean-up database operations after SQL INSERTs (which occur when ejbCreate() is called) when working with CMP entity beans. ejbCreate() is called before database INSERT operations. You need to use ejbPostCreate() to define operations, like set a flag, after INSERT completes successfully.
Can I Map More Than One Table In A Cmp?
No, you cannot map more than one table to a single CMP Entity Bean. CMP has been, in fact, designed to map a single table.
Is Decorator An Ejb Design Pattern?
No. Decorator design pattern, is the one which exhibits very low level runtime polymorphism, for the specific and single object (Instance of the class), but not for atleast for a class. It is the stuff to add specific functionality to a single & pointed object and leaves others like it unmodified. It is having close similarities like aspectJ stuff, but not with EJB stuff.
What Is The Difference Between Ear, Jar And War File?
J2EE defines three types of archives
1. Java Archives (JAR) A JAR file encapsulates one or more Java classes, a manifest, and a descriptor. JAR files are the lowest level of archive. JAR files are used in J2EE for packaging EJBs and client-side Java Applications.
2. Web Archives (WAR) WAR files are similar to JAR files, except that they are specifically for web applications made from Servlets, JSPs, and supporting classes.
3. Enterprise Archives (EAR) ”An EAR file contains all of the components that make up a particular J2EE application.
What Is Re-entrant. Is Session Beans Reentrant. Is Entity Beans Reentrant?
If we define the entity bean as being reentrant, multiple clients can connect to the Entity bean & execute methods within the entity bean concurrently. Container takes care of synchronization. If we define the entity bean as non-reentrant and many clients connect to it concurrently to execute a method, exception is thrown .
How Many Ejb Objects Are Created For A Bean?
For a Session bean - one EJB object for one bean instance.
For entity bean - it depends , if 2 users are accessing one row at time then one EJB object is used for both the beans other wise for each bean one EJB object.
What Is Deployment Descriptor?
Deployment descriptor is a XML file. which is used to locate the web application by container.it includes the details of respective bean.
What Are The Call Back Methods In Entity Bean?
setEntityContext().
ejbCreate().
ejbPostCreate().
ejbActivate().
ejbPassivate().
ejbRemove().
Can A Class Be It's Own Event Handler? Explain How To Implement This.
Sure. an example could be a class that extends Jbutton and implements ActionListener. In the actionPerformed method, put the code to perform when the button is pressed.
Why Does Jcomponent Have Add() And Remove() Methods But Component Does Not?
Because JComponent is a subclass of Container, and can contain other components and jcomponents.
How Would You Create A Button With Rounded Edges?
There’s 2 ways. The first thing is to know that a JButton’s edges are drawn by a Border. so you can override the Button’s paintComponent(Graphics) method and draw a circle or rounded rectangle (whatever), and turn off the border. Or you can create a custom border that draws a circle or rounded rectangle around any component and set the button’s border to it.
If I Wanted To Use A Solarisui For Just A Jtabbedpane, And The Metal Ui For Everything Else, How Would I Do That?
In the UIDefaults table, override the entry for tabbed pane and put in the SolarisUI delegate. (I don’t know it offhand, but I think it’s "com.sun.ui.motiflookandfeel.MotifTabbedPaneUI" - anything simiar is a good .)
What Is The Difference Between The 'font' And 'fontmetrics' Class?
The Font Class is used to render ‘glyphs’ - the characters you see on the screen. FontMetrics encapsulates information about a specific font on a specific Graphics object. (width of the characters, ascent, descent)
What Class Is At The Top Of The Awt Event Hierarchy?
The java.awt.AWTEvent class is the highest-level class in the AWT event-class hierarchy..
Explain How To Render An Html Page Using Only Swing.
Use a JEditorPane or JTextPane and set it with an HTMLEditorKit, then load the text into the pane.
What Is Bean Managed Transaction?
If a developer doesn't want a Container to manage transactions, it's possible to implement all database operations manually by writing the appropriate JDBC code. This often leads to productivity increase, but it makes an Entity Bean incompatible with some databases and it enlarges the amount of code to be written. All transaction management is explicitly performed by a developer.
What Are Transaction Attributes?
The transaction attribute specifies how the Container must manage transactions for a method when a client invokes the method via the enterprise bean’s home or component interface or when the method is invoked as the result of the arrival of a JMS message. (Sun's EJB Specification) Below is a list of transactional attributes
1. NotSupported - transaction context is unspecified.
2. Required - bean's method invocation is made within a transactional context. If a client is not associated with a transaction, a new transaction is invoked automatically.
3. Supports - if a transactional context exists, a Container acts like the transaction attribute is Required, else - like NotSupported.
4. RequiresNew - a method is invoked in a new transaction context.
5. Mandatory - if a transactional context exists, a Container acts like the transaction attribute is Required, else it throws a javax.ejb.TransactionRequiredException.
6. Never - a method executes only if no transaction context is specified.
What Are Transaction Isolation Levels In Ejb?
1. Transaction_read_uncommitted- Allows a method to read uncommitted data from a DB(fast but not wise).
2. Transaction_read_committed- Guarantees that the data you are getting has been committed.
3. Transaction_repeatable_read - Guarantees that all reads of the database will be the same during the transaction (good for read and update operations).
4. Transaction_serializable- All the transactions for resource are performed serial.
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| ServiceNow Most Frequently Asked Latest Advanced Java Interview Questions Answers |
How Ejb Invocation Happens?
Retrieve Home Object reference from Naming Service via JNDI.
Return Home Object reference to the client.
Create a new EJB Object through Home Object interface.
Create EJB Object from the Ejb Object
Return EJB Object reference to the client.
Invoke business method using EJB Object reference.
Delegate request to Bean (Enterprise Bean).
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?
You can pass the HttpSession as parameter to an EJB method, only if all objects in session are serializable.This has to be consider as passed-by-value", that means that its read-only in the EJB. If anything is altered from inside the EJB, it wont be reflected back to the HttpSession of the Servlet Container.The pass-by-reference can be used between EJBs Remote Interfaces, as they are remote references. While it IS possible to pass an HttpSession as a parameter to an EJB object, it is considered to be bad practice in terms of object oriented design. This is because you are creating an unnecessary coupling between back-end objects (ejbs) and front-end objects (HttpSession). Create a higher-level of abstraction for your ejbs api. Rather than passing the whole, fat, HttpSession (which carries with it a bunch of http semantics), create a class that acts as a value object (or structure) that holds all the data you need to pass back and forth between front-end/back-end. Consider the case where your ejb needs to support a non-http-based client. This higher level of abstraction will be flexible enough to support it.
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?
The EJB container maintains an instance pool. The container uses these instances for the EJB Home reference irrespective of the client request. while refering the EJB Object classes the container creates a separate instance for each client request. The instance pool maintainence is up to the implementation of the container. If the container provides one, it is available otherwise it is not mandatory for the provider to implement it. Having said that, yes most of the container providers implement the pooling functionality to increase the performance of the application server. The way it is implemented is again up to the implementer.
Can The Primary Key In The Entity Bean Be A Java Primitive Type Such As Int?
The primary key can't be a primitive type--use the primitive wrapper classes, instead. For example, you can use java.lang.Integer as the primary key class, but not int (it has to be a class, not a primitive)
Can You Control When Passivation Occurs?
The developer, according to the specification, cannot directly control when passivation occurs. Although for Stateful Session Beans, the container cannot passivate an instance that is inside a transaction. So using transactions can be a a strategy to control passivation.
The ejbPassivate() method is called during passivation, so the developer has control over what to do during this exercise and can implement the require optimized logic.
Some EJB containers, such as BEA WebLogic, provide the ability to tune the container to minimize passivation calls.
Taken from the WebLogic 6.0 DTD -"The passivation-strategy can be either "default" or "transaction". With the default setting the container will attempt to keep a working set of beans in the cache. With the "transaction" setting, the container will passivate the bean after every transaction (or method call for a non-transactional invocation).
What Is The Advantage Of Using Entity Bean For Database Operations, Over Directly Using Jdbc Api To Do Database Operations? When Would I Use One Over The Other?
Entity Beans actually represents the data in a database. It is not that Entity Beans replaces JDBC API. There are two types of Entity Beans Container Managed and Bean Mananged. In Container Managed Entity Bean - Whenever the instance of the bean is created the container automatically retrieves the data from the DB/Persistance storage and assigns to the object variables in bean for user to manipulate or use them. For this the developer needs to map the fields in the database to the variables in deployment descriptor files (which varies for each vendor).
In the Bean Managed Entity Bean - The developer has to specifically make connection, retrive values, assign them to the objects in the ejbLoad() which will be called by the container when it instatiates a bean object. Similarly in the ejbStore() the container saves the object values back the the persistance storage. ejbLoad and ejbStore are callback methods and can be only invoked by the container. Apart from this, when you use Entity beans you dont need to worry about database transaction handling, database connection pooling etc. which are taken care by the ejb container. But in case of JDBC you have to explicitly do the above features. what suresh told is exactly perfect. ofcourse, this comes under the database transations, but i want to add this. the great thing about the entity beans of container managed, whenever the connection is failed during the transaction processing, the database consistancy is mantained automatically. the container writes the data stored at persistant storage of the entity beans to the database again to provide the database consistancy. where as in jdbc api, we, developers has to do manually.
What Is Ejb Ql?
EJB QL is a Query Language provided for navigation across a network of enterprise beans and dependent objects defined by means of container managed persistence. EJB QL is introduced in the EJB 2.0 specification. The EJB QL query language defines finder methods for entity beans with container managed persistenceand is portable across containers and persistence managers. EJB QL is used for queries of two types of finder methods: Finder methods that are defined in the home interface of an entity bean and which return entity objects. Select methods, which are not exposed to the client, but which are used by the Bean Provider to select persistent values that are maintained by the Persistence Manager or to select entity objects that are related to the entity bean on which the query is defined.
Brief Description About Local Interfaces?
EEJB was originally designed around remote invocation using the Java Remote Method Invocation (RMI) mechanism, and later extended to support to standard CORBA transport for these calls using RMI/IIOP. This design allowed for maximum flexibility in developing applications without consideration for the deployment scenario, and was a strong feature in support of a goal of component reuse in J2EE.
Many developers are using EJBs locally -- that is, some or all of their EJB calls are between beans in a single container.
With this feedback in mind, the EJB 2.0 expert group has created a local interface mechanism. The local interface may be defined for a bean during development, to allow streamlined calls to the bean if a caller is in the same container. This does not involve the overhead involved with RMI like marshalling etc. This facility will thus improve the performance of applications in which co-location is planned.
Local interfaces also provide the foundation for container-managed relationships among entity beans with container-managed persistence.
What Are The Special Design Care That Must Be Taken When You Work With Local Interfaces?
EIt is important to understand that the calling semantics of local interfaces are different from those of remote interfaces. For example, remote interfaces pass parameters using call-by-value semantics, while local interfaces use call-by-reference.
This means that in order to use local interfaces safely, application developers need to carefully consider potential deployment scenarios up front, then decide which interfaces can be local and which remote, and finally, develop the application code with these choices in mind.
While EJB 2.0 local interfaces are extremely useful in some situations, the long-term costs of these choices, especially when changing requirements and component reuse are taken into account, need to be factored into the design decision.
What Happens If Remove( ) Is Never Invoked On A Session Bean?
In case of a stateless session bean it may not matter if we call or not as in both cases nothing is done. The number of beans in cache is managed by the container.
In case of stateful session bean, the bean may be kept in cache till either the session times out, in which case the bean is removed or when there is a requirement for memory in which case the data is cached and the bean is sent to free pool.
How Can I Call One Ejb From Inside Of Another Ejb?
EJBs can be clients of other EJBs. It just works. Use JNDI to locate the Home Interface of the other bean, then acquire an instance reference, and so forth.
What Is An Ejb Context?
EJBContext is an interface that is implemented by the container, and it is also a part of the bean-container contract. Entity beans use a subclass of EJBContext called EntityContext. Session beans use a subclass called SessionContext. These EJBContext objects provide the bean class with information about its container, the client using the bean and the bean itself. They also provide other functions. See the API docs and the spec for more details.
What Are The Two Important Tcp Socket Classes?
Socket and ServerSocket.
ServerSocket is used for normal two-way socket communication.
Socket class allows us to read and write through the sockets. getInputStream() and getOutputStream() are the two methods available in Socket class.
What Technologies Are Included In J2ee?
The main technologies in J2EE are: Enterprise JavaBeansTM (EJBsTM), JavaServer PagesTM (JSPsTM), Java Servlets, the Java Naming and Directory InterfaceTM (JNDITM), the Java Transaction API (JTA), CORBA, and the JDBCTM data access API.
What Is The Difference Between Ejb And Java Beans?
EJB is a specification for J2EE server, not a product; Java beans may be a graphical component in IDE.
What Is Ejb Role In J2ee?
EJB technology is the core of J2EE. It enables developers to write reusable and portable server-side business logic for the J2EE platform.
Tell Me Something About Local Interfaces.
EJB was originally designed around remote invocation using the Java Remote Method Invocation (RMI) mechanism, and later extended to support to standard CORBA transport for these calls using RMI/IIOP. This design allowed for maximum flexibility in developing applications without consideration for the deployment scenario, and was a strong feature in support of a goal of component reuse in J2EE. Many developers are using EJBs locally, that is, some or all of their EJB calls are between beans in a single container. With this feedback in mind, the EJB 2.0 expert group has created a local interface mechanism. The local interface may be defined for a bean during development, to allow streamlined calls to the bean if a caller is in the same container. This does not involve the overhead involved with RMI like marshalling etc. This facility will thus improve the performance of applications in which co-location is planned. Local interfaces also provide the foundation for container-managed relationships among entity beans with container-managed persistence.
What Is Enterprise Javabeans (ejb) Container?
It manages the execution of enterprise beans for J2EE applications. Enterprise beans and their container run on the J2EE server.
What Is In-memory Replication?
The process by which the contents in the memory of one physical m/c are replicated in all the m/c in the cluster is called in-memory replication.
What Is Ripple Effect?
The process of propagating the changes in the properties of a server group during runtime to all the associated clones is called Ripple Effect.
What Is A Clone?
The copies of a server group are called Clones. But unlike a Server Group Clones are associated with a node and are real server process running in that node.
What Are The Types Of Scaling?
There are two types of scaling: Vertical Scaling and Horizontal Scaling.
Vertical Scaling - When multiple server clones of an application server are defined on the same physical m/c, it is called Vertical Scaling. The objective is to use the processing power of that m/c more efficiently.
Horizontal Scaling - When Clones of an application server are defined on multiple physical m/c, it is called Horizontal Scaling. The objective is to use more than one less powerful m/c more efficiently.
What Is A Server Group?
A server group is a template of an Application Server(and its contents) i.e, it is a logical representation of the application server. It has the same structure and attributes as the real Application Server, but it is not associated with any node, and does not correspond to any real server process running on any node.
What Is The New Basic Requirement For A Cmp Entity Bean Class In 2.0 From That Of Ejb 1.1?
It must be abstract class. The container extends it and implements methods which are required for managing the relationships.
What's New In The Ejb 2.0 Specification?
Following are some of the main features supported in EJB 2.0
1. Integration of EJB with JMS,
2. Message Driven Beans,
3. Implement additional Business methods in Home interface which are not specific for bean instance, EJB QL.
How Can I Access Ejb From Asp?
We can use the Java 2 Platform, Enterprise Edition Client Access Services (J2EETM CAS) COM Bridge 1.0, currently downloadable from Sun.
What Is The Relationship Between Local Interfaces And Container-managed Relationships?
Entity beans that have container-managed relationships with other entity beans, must be accessed in the same local scope as those related beans, and therefore typically provide a local client view. In order to be the target of a container-managed relationship, an entity bean with container-managed persistence must provide a local interface.
What Is Ejbdoclet?
EJBDoclet is an open source JavaDoc doclet that generates a lot of the EJB related source files from custom JavaDoc comments tags embedded in the EJB source file.
What Is The Difference Between Session And Entity Beans?
An entity bean represents persistent global data from the database; a session bean represents transient user-specific data that will die when the user disconnects (ends his session). Generally, the session beans implement business methods (e.g. Bank.transferFunds) that call entity beans (e.g. Account.deposit, Account.withdraw)
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 a class. Static initializer blocks are also typically used to initialize static fields - which may be illegal in EJB if they are read/write - In EJB this can be achieved by including the code in either the ejbCreate(), setSessionContext() or setEntityContext() methods.
What Are Local Interfaces? Describe.
EJB was originally designed around remote invocation using the Java Remote Method Invocation (RMI) mechanism, and later extended to support to standard CORBA transport for these calls using RMI/IIOP. This design allowed for maximum flexibility in developing applications without consideration for the deployment scenario, and was a strong feature in support of a goal of component reuse in J2EE. Many developers are using EJBs locally, that is, some or all of their EJB calls are between beans in a single container. With this feedback in mind, the EJB 2.0 expert group has created a local interface mechanism. The local interface may be defined for a bean during development, to allow streamlined calls to the bean if a caller is in the same container. This does not involve the overhead involved with RMI like marshalling etc. This facility will thus improve the performance of applications in which co-location is planned. Local interfaces also provide the foundation for container-managed relationships among entity beans with container-managed persistence.
What Is Difference Between Ejb 1.1 And Ejb 2.0?
The bulk of the changes in EJB 2.0 are found in the definition of a new CMP component model. It’s radically different from the old CMP model because it introduces an entirely new participant, the persistence manager, and a completely new way of defining container-managed fields, as well as relationships with other beans and dependent objects.
What Is The Difference Between Ejbcreate() And Ejbpostcreate?
The purpose of ejbPostCreate() is to perform clean-up database operations after SQL INSERTs (which occur when ejbCreate() is called) when working with CMP entity beans. ejbCreate() is called before database INSERT operations. You need to use ejbPostCreate() to define operations, like set a flag, after INSERT completes successfully.
Can I Map More Than One Table In A Cmp?
No, you cannot map more than one table to a single CMP Entity Bean. CMP has been, in fact, designed to map a single table.
Is Decorator An Ejb Design Pattern?
No. Decorator design pattern, is the one which exhibits very low level runtime polymorphism, for the specific and single object (Instance of the class), but not for atleast for a class. It is the stuff to add specific functionality to a single & pointed object and leaves others like it unmodified. It is having close similarities like aspectJ stuff, but not with EJB stuff.
What Is The Difference Between Ear, Jar And War File?
J2EE defines three types of archives
1. Java Archives (JAR) A JAR file encapsulates one or more Java classes, a manifest, and a descriptor. JAR files are the lowest level of archive. JAR files are used in J2EE for packaging EJBs and client-side Java Applications.
2. Web Archives (WAR) WAR files are similar to JAR files, except that they are specifically for web applications made from Servlets, JSPs, and supporting classes.
3. Enterprise Archives (EAR) ”An EAR file contains all of the components that make up a particular J2EE application.
What Is Re-entrant. Is Session Beans Reentrant. Is Entity Beans Reentrant?
If we define the entity bean as being reentrant, multiple clients can connect to the Entity bean & execute methods within the entity bean concurrently. Container takes care of synchronization. If we define the entity bean as non-reentrant and many clients connect to it concurrently to execute a method, exception is thrown .
How Many Ejb Objects Are Created For A Bean?
For a Session bean - one EJB object for one bean instance.
For entity bean - it depends , if 2 users are accessing one row at time then one EJB object is used for both the beans other wise for each bean one EJB object.
What Is Deployment Descriptor?
Deployment descriptor is a XML file. which is used to locate the web application by container.it includes the details of respective bean.
What Are The Call Back Methods In Entity Bean?
setEntityContext().
ejbCreate().
ejbPostCreate().
ejbActivate().
ejbPassivate().
ejbRemove().
Can A Class Be It's Own Event Handler? Explain How To Implement This.
Sure. an example could be a class that extends Jbutton and implements ActionListener. In the actionPerformed method, put the code to perform when the button is pressed.
Why Does Jcomponent Have Add() And Remove() Methods But Component Does Not?
Because JComponent is a subclass of Container, and can contain other components and jcomponents.
How Would You Create A Button With Rounded Edges?
There’s 2 ways. The first thing is to know that a JButton’s edges are drawn by a Border. so you can override the Button’s paintComponent(Graphics) method and draw a circle or rounded rectangle (whatever), and turn off the border. Or you can create a custom border that draws a circle or rounded rectangle around any component and set the button’s border to it.
If I Wanted To Use A Solarisui For Just A Jtabbedpane, And The Metal Ui For Everything Else, How Would I Do That?
In the UIDefaults table, override the entry for tabbed pane and put in the SolarisUI delegate. (I don’t know it offhand, but I think it’s "com.sun.ui.motiflookandfeel.MotifTabbedPaneUI" - anything simiar is a good .)
What Is The Difference Between The 'font' And 'fontmetrics' Class?
The Font Class is used to render ‘glyphs’ - the characters you see on the screen. FontMetrics encapsulates information about a specific font on a specific Graphics object. (width of the characters, ascent, descent)
What Class Is At The Top Of The Awt Event Hierarchy?
The java.awt.AWTEvent class is the highest-level class in the AWT event-class hierarchy..
Explain How To Render An Html Page Using Only Swing.
Use a JEditorPane or JTextPane and set it with an HTMLEditorKit, then load the text into the pane.
https://mytecbooks.blogspot.com/2019/06/servicenow-advanced-java-interview.html