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.
SOURCE : www.referjava.com
Sunday, February 4, 2007
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.
SOURCE : www.referjava.com
SOURCE : www.referjava.com
What is the difference between Message Driven Beans and Stateless Session beans?
In several ways, the dynamic creation and allocation of message-driven bean instances mimics the behavior of stateless session EJB instances, which exist only for the duration of a particular method call. However, message-driven beans are different from stateless session EJBs (and other types of EJBs) in several significant ways:
Message-driven beans process multiple JMS messages asynchronously, rather than processing a serialized sequence of method calls.
Message-driven beans have no home or remote interface, and therefore cannot be directly accessed by internal or external clients. Clients interact with message-driven beans only indirectly, by sending a message to a JMS Queue or Topic.
Note: Only the container directly interacts with a message-driven bean by creating bean instances and passing JMS messages to those instances as necessary.
The Container maintains the entire lifecycle of a message-driven bean; instances cannot be created or removed as a result of client requests or other API calls.
SOURCE : www.referjava.com
Message-driven beans process multiple JMS messages asynchronously, rather than processing a serialized sequence of method calls.
Message-driven beans have no home or remote interface, and therefore cannot be directly accessed by internal or external clients. Clients interact with message-driven beans only indirectly, by sending a message to a JMS Queue or Topic.
Note: Only the container directly interacts with a message-driven bean by creating bean instances and passing JMS messages to those instances as necessary.
The Container maintains the entire lifecycle of a message-driven bean; instances cannot be created or removed as a result of client requests or other API calls.
SOURCE : www.referjava.com
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.
SOURCE : www.referjava.com
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.
SOURCE : www.referjava.com
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.
SOURCE : www.referjava.com
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.
SOURCE : www.referjava.com
Brief description 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.
SOURCE : www.referjava.com
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.
SOURCE : www.referjava.com
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.
SOURCE : www.referjava.com
SOURCE : www.referjava.com
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
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.
SOURCE : www.referjava.com
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.
SOURCE : www.referjava.com
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).
SOURCE : www.referjava.com
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).
SOURCE : www.referjava.com
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)
SOURCE : www.referjava.com
SOURCE : www.referjava.com
The EJB container implements the EJBHome and EJBObject classes. For every request from a unique client, does the container create a separate instance
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.
SOURCE : www.referjava.com
SOURCE : www.referjava.com
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 it?s read-only in the EJB. If anything is altered from inside the EJB, it won?t 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 ejb?s 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.
SOURCE : www.referjava.com
SOURCE : www.referjava.com
How EJB Invocation happens?
Step 1: Retrieve Home Object reference from Naming Service via JNDI.
step 2: Return Home Object reference to the client.
step 3: Create me a new EJB Object through Home Object interface.
step 4: Create EJB Object from the Ejb Object
step 5: Return EJB Object reference to the client.
step 6: Invoke business method using EJB Object reference.
step 7: Delegate request to Bean (Enterprise Bean).
SOURCE : www.referjava.com
step 2: Return Home Object reference to the client.
step 3: Create me a new EJB Object through Home Object interface.
step 4: Create EJB Object from the Ejb Object
step 5: Return EJB Object reference to the client.
step 6: Invoke business method using EJB Object reference.
step 7: Delegate request to Bean (Enterprise Bean).
SOURCE : www.referjava.com
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.
SOURCE : www.referjava.com
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.
SOURCE : www.referjava.com
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.
SOURCE : www.referjava.com
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.
SOURCE : www.referjava.com
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.
SOURCE : www.referjava.com
SOURCE : www.referjava.com
Can Entity Beans have no create() methods?
Yes. In some cases the data is inserted NOT using Java application, so you may only need to retrieve the information, perform its processing, but not create your own information of this kind.
SOURCE : www.referjava.com
SOURCE : www.referjava.com
What is software architecture of EJB?
Session and Entity EJBs consist of 4 and 5 parts respetively:
1. A remote interface (a client interacts with it),
2. A home interface (used for creating objects and for declaring business methods),
3. A bean object (an object, which actually performs business logic and EJB-specific operations).
4. A deployment descriptor (an XML file containing all information required for maintaining the EJB) or a set of deployment descriptors (if you are using some container-specific features).
5.A Primary Key class - is only Entity bean specific.
SOURCE : www.referjava.com
1. A remote interface (a client interacts with it),
2. A home interface (used for creating objects and for declaring business methods),
3. A bean object (an object, which actually performs business logic and EJB-specific operations).
4. A deployment descriptor (an XML file containing all information required for maintaining the EJB) or a set of deployment descriptors (if you are using some container-specific features).
5.A Primary Key class - is only Entity bean specific.
SOURCE : www.referjava.com
What are the callback methods in Entity beans?
The bean class defines create methods that match methods in the home interface and business methods that match methods in the remote interface. The bean class also implements a set of callback methods that allow the container to notify the bean of events in its life cycle. The callback methods are defined in the javax.ejb.EntityBean interface that is implemented by all entity beans.The EntityBean interface has the following definition. Notice that the bean class implements these methods.
public interface javax.ejb.EntityBean {
public void setEntityContext();
public void unsetEntityContext();
public void ejbLoad();
public void ejbStore();
public void ejbActivate();
public void ejbPassivate();
public void ejbRemove();
}
SOURCE : www.referjava.com
public interface javax.ejb.EntityBean {
public void setEntityContext();
public void unsetEntityContext();
public void ejbLoad();
public void ejbStore();
public void ejbActivate();
public void ejbPassivate();
public void ejbRemove();
}
SOURCE : www.referjava.com
What is the difference between Container-Managed Persistent (CMP) bean and Bean-Managed Persistent(BMP) ?
Container-managed persistence beans are the simplest for the bean developer to create and the most difficult for the EJB server to support. This is because all the logic for synchronizing the bean's state with the database is handled automatically by the container. This means that the bean developer doesn't need to write any data access logic, while the EJB server is supposed to take care of all the persistence needs automatically. With CMP, the container manages the persistence of the entity bean. A CMP bean developer doesn't need to worry about JDBC code and transactions, because the Container performs database calls and transaction management instead of the programmer. Vendor tools are used to map the entity fields to the database and absolutely no database access code is written in the bean class. All table mapping is specified in the deployment descriptor. Otherwise, a BMP bean developer takes the load of linking an application and a database on his shoulders.
The bean-managed persistence (BMP) enterprise bean manages synchronizing its state with the database as directed by the container. The bean uses a database API to read and write its fields to the database, but the container tells it when to do each synchronization operation and manages the transactions for the bean automatically. Bean-managed persistence gives the bean developer the flexibility to perform persistence operations that are too complicated for the container or to use a data source that is not supported by the container.BMP beans are not 100% database-independent, because they may contain database-specific code, but CMP beans are unable to perform complicated DML (data manipulation language) statements. EJB 2.0 specification introduced some new ways of querying database (by using the EJB QL - query language).
SOURCE : www.referjava.com
The bean-managed persistence (BMP) enterprise bean manages synchronizing its state with the database as directed by the container. The bean uses a database API to read and write its fields to the database, but the container tells it when to do each synchronization operation and manages the transactions for the bean automatically. Bean-managed persistence gives the bean developer the flexibility to perform persistence operations that are too complicated for the container or to use a data source that is not supported by the container.BMP beans are not 100% database-independent, because they may contain database-specific code, but CMP beans are unable to perform complicated DML (data manipulation language) statements. EJB 2.0 specification introduced some new ways of querying database (by using the EJB QL - query language).
SOURCE : www.referjava.com
What is the differnce between Thread and Process?
A process is a separate group of Threads. Every program generates its own process. If you create a Thread in your Java program, it runs in the process that was created when the JVM started. You create a Thread to do something internally in your program, and you create a process to run a separate program.
SOURCE : www.referjava.com
SOURCE : www.referjava.com
What method must be implemented by all threads?
All tasks must implement the run() method, whether they are a subclass ofThread or implement the Runnable interface.
SOURCE : www.referjava.com
SOURCE : www.referjava.com
What is the difference between a Window and a Frame?
The Frame class extends Window to define a main application window that can have a menu bar.
SOURCE : www.referjava.com
SOURCE : www.referjava.com
What is the difference between the paint() and repaint() method
The paint() method supports painting via a Graphics object. The repaint() method is used to cause paint() to be invoked by the AWT painting thread.
SOURCE : www.referjava.com
SOURCE : www.referjava.com
What is the ServletConfig() and why are using ServletConfig
This interface is implemented by services in order to pass configuration information to a servlet when it is first loaded.A service writer implementing this interface must write methods for the servlet to use to get its initialization parameters and the context in which it is running. public interface ServletConfig.
SOURCE : www.referjava.com
SOURCE : www.referjava.com
What is Server-Side Includes (SSI)?
Server-Side Includes allows embedding servlets within HTML pages using a special servlet tag. In many servlets that support servlets, a page can be processed by the server to include output from servlets at certain points inside the HTML page. This is accomplished using a special internal SSINCLUDE, which processes the servlet tags. SSINCLUDE servlet will be invoked whenever a file with an. shtml extension is requested. So HTML files that include server-side includes must be stored with an .shtml extension.
SOURCE : www.referjava.com
SOURCE : www.referjava.com
What are the advantage of using Sessions over Cookies and URLReWriting?
Sessions are more secure and fast becasue they are stored at serverside. But Sessions has to be used combindly with Cookies or URLReWriting for mainting the client id that is sessionid at client side.
Cookies are stored at client side so some clients may disable cookies so we may not sure that the cookies which we are mainting may work or not but in sessions cookies are disable we can maintain our sessionid using URLReWriting .
In URLReWriting we can't maintain large data because it leads to network traffic and access may be become slow.Where as in seesions will not maintain the data which we have to maintain instead we will maintain only the session id.
SOURCE : www.referjava.com
Cookies are stored at client side so some clients may disable cookies so we may not sure that the cookies which we are mainting may work or not but in sessions cookies are disable we can maintain our sessionid using URLReWriting .
In URLReWriting we can't maintain large data because it leads to network traffic and access may be become slow.Where as in seesions will not maintain the data which we have to maintain instead we will maintain only the session id.
SOURCE : www.referjava.com
Why we are used setMaxAge() and getMaxAge() in Cookies ?
setMaxAge
public void setMaxAge(int expiry)
Sets the maximum age of the cookie.The cookie will expire after that many seconds have passed.Negative values indicate the default behaviour:the cookie is not stored persistently, and will be deleted when the user agent exits.A zero value causes the cookie to be deleted
getMaxAge():
public int getMaxAge()
Returns the maximum specified age of the cookie. If none was specified, a negative value is returned, indicating the default behaviour described with setMaxAge.
SOURCE : www.referjava.com
public void setMaxAge(int expiry)
Sets the maximum age of the cookie.The cookie will expire after that many seconds have passed.Negative values indicate the default behaviour:the cookie is not stored persistently, and will be deleted when the user agent exits.A zero value causes the cookie to be deleted
getMaxAge():
public int getMaxAge()
Returns the maximum specified age of the cookie. If none was specified, a negative value is returned, indicating the default behaviour described with setMaxAge.
SOURCE : www.referjava.com
What are the methods in HttpSession and use of those methods?
a) getCreationTime()
Returns the time at which this session representation was created.
b) getId()
Returns the identifier assigned to this session.
c) getLastAccessedTime()
Returns the last time the client sent a request carrying the identifier assigned to the session.
d) getSessionContext()
Returns the context in which this session is bound.
e) getValue(String)
Returns the object bound to the given name in the session's application layer data.
f) getValueNames()
Returns an array of the names of all the application layer data objects bound into the
session.
g) invalidate()
Causes this representation of the session to be invalidated and removed from its context.
h) isNew()
A session is considered to be "new" if it has been created by the server, but the client has
not yet acknowledged joining the session.
j) putValue(String, Object)
Binds the specified object into the session's application layer data with the given name.
k) removeValue(String)
Removes the object bound to the given name in the session's application layer data.
SOURCE : www.referjava.com
Returns the time at which this session representation was created.
b) getId()
Returns the identifier assigned to this session.
c) getLastAccessedTime()
Returns the last time the client sent a request carrying the identifier assigned to the session.
d) getSessionContext()
Returns the context in which this session is bound.
e) getValue(String)
Returns the object bound to the given name in the session's application layer data.
f) getValueNames()
Returns an array of the names of all the application layer data objects bound into the
session.
g) invalidate()
Causes this representation of the session to be invalidated and removed from its context.
h) isNew()
A session is considered to be "new" if it has been created by the server, but the client has
not yet acknowledged joining the session.
j) putValue(String, Object)
Binds the specified object into the session's application layer data with the given name.
k) removeValue(String)
Removes the object bound to the given name in the session's application layer data.
SOURCE : www.referjava.com
What are the different servers available for developing and deploying Servlets?
a) JRun2.0--Allaire
b) Apache --jserv
c) jwsdk2.0 --sun
d) servletexec
e) Tomcat webserver--tomcat
f) Weblogic AS--BEA Systems
g) NetDynamics5.0--sun
h) Iplanet--sun&netscape
i) Netscape--netscape
g) IBM websphere--IBM
h) oracle--oracle
i) Proton-Pramati technologies
SOURCE : www.referjava.com
b) Apache --jserv
c) jwsdk2.0 --sun
d) servletexec
e) Tomcat webserver--tomcat
f) Weblogic AS--BEA Systems
g) NetDynamics5.0--sun
h) Iplanet--sun&netscape
i) Netscape--netscape
g) IBM websphere--IBM
h) oracle--oracle
i) Proton-Pramati technologies
SOURCE : www.referjava.com
Is it possible to communicate from an applet to servlet and how many ways and how?
Yes, there are three ways to communicate from an applet to servlet and they are:
a) HTTP Communication(Text-based and object-based)
b) Socket Communication
c) RMI Communication
(You can say, by using URL object open the connection to server and get the InputStream from
URLConnection object).
Steps involved for applet-servlet communication:
step: 1 Get the server URL.
URL url = new URL();
step: 2 Connect to the host
URLConnection Con = url.openConnection();
step: 3 Initialize the connection
Con.setUseCatches(false):
Con.setDoOutput(true);
Con.setDoInput(true);
step: 4 Data will be written to a byte array buffer so that we can tell the server the length of the data.
ByteArrayOutputStream byteout = new ByteArrayOutputStream();
step: 5 Create the OutputStream to be used to write the data to the buffer.
DataOutputStream out = new DataOutputStream(byteout);
SOURCE : www.referjava.com
a) HTTP Communication(Text-based and object-based)
b) Socket Communication
c) RMI Communication
(You can say, by using URL object open the connection to server and get the InputStream from
URLConnection object).
Steps involved for applet-servlet communication:
step: 1 Get the server URL.
URL url = new URL();
step: 2 Connect to the host
URLConnection Con = url.openConnection();
step: 3 Initialize the connection
Con.setUseCatches(false):
Con.setDoOutput(true);
Con.setDoInput(true);
step: 4 Data will be written to a byte array buffer so that we can tell the server the length of the data.
ByteArrayOutputStream byteout = new ByteArrayOutputStream();
step: 5 Create the OutputStream to be used to write the data to the buffer.
DataOutputStream out = new DataOutputStream(byteout);
SOURCE : www.referjava.com
Why should we go for interservlet communication?
Servlets running together in the same server communicate with each other in several ways.
The three major reasons to use interservlet communication are:
a) Direct servlet manipulation - allows to gain access to the other currently loaded servlets and perform certain tasks (through the ServletContext object)
b) Servlet reuse - allows the servlet to reuse the public methods of another servlet.
c) Servlet collaboration - requires to communicate with each other by sharing specific information (through method invocation)
SOURCE : www.referjava.com
The three major reasons to use interservlet communication are:
a) Direct servlet manipulation - allows to gain access to the other currently loaded servlets and perform certain tasks (through the ServletContext object)
b) Servlet reuse - allows the servlet to reuse the public methods of another servlet.
c) Servlet collaboration - requires to communicate with each other by sharing specific information (through method invocation)
SOURCE : www.referjava.com
Subscribe to:
Posts (Atom)
