J2EE(Java 2 Enterprise Edition
)
It is the big concept having
large nos of technology in it such as EJB,JMS,JAVA IDL etc
Here we will talk about the
EJB(Enterprise Java Bean) only
EJB(Enterprise Java Bean) :
This is a J2EE technology which is use to prepare a Bean(Known as the server
side software component )for the Java enterprise edition.
Now what the Enterprise edition
stand for:
Enterprise edition stand for
the 3 tier architecture (CLIENT-MIDDLEWARE-DATABSE)
BEANS:
Bean is server side component
and it is deployed in a container that are placed in the Application server.
What is Container and
AS(Application Server):
Container : Generally the
Bean(Sever side software component ) is logic which we want to be perform for
us in the Business but it requires some platform to be operated and that plate
form is given by the container and it is in the AS.
Now in one AS there can be many
container and in one container there can be many beans
But before starting the Concept of the Beans there are
certain think that has to been needed to understand some of the concept of the
JAVA they are as follows:
1)JAVA RMI-IIOP
2)JNDI
3)JDBC
4)JTA-JTS
5)JMS
6)EJB
7)JSP
8)Java IDL
9)JAVA Mail
9)Connector
10)XML(Extensible mark up language)
1) Java RMI: this is the facilities
which is provided by the java for the invocation of the remote method (the
method which is not present in our M/c or in our JVM with the help of the
Interface.
2) JNDI: this include the Naming
directory which is used for the look up the remote component ie beans during
the operation.
3) JDBC : it is for the database
connection and it is similar to the ODBC which is provided by the Microsoft.
4) JTA and JTS: this both are the api
produce by the sun to help to create the Transaction Management which is of
great important for the AS further explained.
5) JMS : this is for the Messaging
service which deals with the transfer of message between the object which
required during the application as we required that our beans talk with each
other to facilitate the application.
6) JSP: this is the scripting
language use to built the pages in the java language. It is similar to the
servlets infect they are complied into the servlets. only the difference is
that JSP is not truly 100% java pages they are concentrated on the look and
feel factors
7) Java IDL: this is the beautiful
concept with can be simply define as implementation of CORBA in java. ie(it is
the specific implementation of CORBA in java side)
8) Java Mail: it is use for the
mailing service and is not much imp for us.
9) Connector: To ask.
10) XML : this
is the language which is having the different concept for the different
application for EJB it work as the descriptor and of the JSP it work as the
data document format for authoring web script.
Now lets talk
about the Container and The AS(Application Server)
(Application
Server)As provided the following things
Resource
management – deal with the database connection,pool,threads,socket conection
Life cycle:
State
management :it look the state of the bean (share the same state bean with the
client)
Transaction:Allow
the user to use the same data access at the same time if any one change then
that data is changed (Whole or Rollback) .
Security:
which user is allowed to see the bean and who is blocked
Persistence
:It maintain the Data in the Formate which can be easily read and can I\be out
in the Db at the definite point of time.(It hold the data at one point of time
write it back to the Db at the other point of time)
Remote
accessibility: This the concept that is much imp for the Enterprise edition as
the client is now knowing that the component to which contact is either lying
on its own machine or it is residing on the other M/c .
So it is much
important to select the proper AS as it perform most of the typical job for the
J2EE which client is not to be worried . There are different AS available in
the market BEA weblogic ,Oracle Oracle9ias ,IBM Websphere etc etc
All have there
own concept and Container but is developed under the common API of the J2ee.
Now what is
the different between Container and the AS:
Theoretically
it is difficult to make the difference between the AS and the container but we
can say that beans are placed in the Container and Container is Placed in the
AS
(More over it
is also clear that container of company cannot be used in other AS ie container
used by the weblogic cannot be used by the Oracle9ias.)
Now we will
talk about the EJB:
It has two
version EJB 1.0 and EJB1. 1 the main difference is that EJB1.1 has the concept
of ENTITY Beans.
1)SESSION
BEANS:
a)STATEFUL
b) STATELESS
SESSION BEANS
2)ENTITY
BEANS:
Manage by two ways
a)Container
Manage Persistence.
b)Bean Manage
Persistence.
1)SESSION
BEANS:
The word
session itself indicate that it define the Session for a particular Client.
Generally the Business logic which we want to deal with is written in this
Beans.
Characteristic
of Session Beans are:
1)They cannot
be share that means that Once it is allocated to a Particular client then
unless and until it is removed (set free from the client ) it is not been
available to the other (No two client can share the same Session bean at the
same time)
2)It can talk
to the Entity beans for its fulfillment of purpose .
3)It can talk
with 2 or more beans for this.
Type of the
Session Beans:
a)STATEFUL
SESSION BEAN:
This is the
Session Bean which maintain its state in normal manner speaking that this type
of the Bean is used in e-commerce application in which you want that the client
should know what he had purchase in given interval of time.
If the client
is purchasing the item and again go to the next counter to purchase the next
item and if he want to know what he had purchase in the previous counter he can
use this type of beans in which the state of the session beans is maintained
and if required this state full beans is given to the user with full state
having the information of the previous encounter.
b)STATELESS
SESSION BEAN:
This is the
Session Bean which did not maintain the state for it use. This type of the
application is generally used where the back information is of no use. Ie the
validation of the visa card or the credit card only thing to do is take the
card no and its user signature and validate it with the data base data and
return true or false or it can be used in the application of transferring the
mail to the client about the receiving of the amount or cheque.
ENTIY BEANS:
Why the
concept of the Entity beans comes in to the picture when we are having the
concept of the session beans. The main reasons is that we want the persistence
in our data and to maintain the transaction fast and easily. It generally
define the Data at one point of time and write back the data to the database in
the next movement of time. So if the system is crashed the data can be easily
available from the Entity beans And it is sure that Entity beans is inherently
STATFUL as the data maintained it state.
Now there are
two ways to handle the Entity Beans:
1)Container
Manage Persistence:
2)Bean Manage
Persistence:
1)Container
Manage Persistence:
As the name
itself suggest that in this the overall command of the Beans is in the hand of
the Container in which it is deployed. Not much versatility is available for
the user in this management . In coding section we can say that in container
manage persistence the client is not required to write the SQL quarries the
container use its internal inbuild quarries for fetching and manipulating the
result.
2)Beans Manage
Persistence:
In this the
Entity beans is manage by itself . here the user write it own querries for
fetching of the result and manipulating the result it has high versatility than
the Container manage persistence
Characteristic
of the Entity beans
1)It can be
shared between the user ie. Two user can use the same entity beans at the same
time.
2)It maintain
the Data persistence.
3)It maintain
the state as it by default STATEFUL Beans
Q)Then what is
the main difference between Session and Entity Beans
(R-Relation,S-Share,S-State,P-Persistence)
1)The session
beans cannot be Shared but the Entity Beans can be shared.
2)There can be
relation between entity beans ie. one entity bean can have the internal
relation with other entity beans but this is not possible with Session beans.
3)Entity
always maintain the State but in case of Session only the STATEFUL Session
beans maintain the state.
4)Entity beans
maintain the persistence of the data. Where as the session didn’t.
For Entity
Beans: Beans manage persistence
Activate()—container-no need for code
Lode(select)—pk-
this.entityContext.getPrimaryKey()
1)connection
is obtained
2)Prepared
statement
3)select query
Store(update)—pk-
this.entityContext.getPrimaryKey()
1)connection
is obtained
2)Prepared
statement
3)update
query
Passivate()-Container— no need for code
Create(insert)—argument gives the id
1)connection
is obtained
2)Prepared
statement
3)Insert query
Remove(delete)—pk-
this.entityContext.getPrimaryKey()
1)connection
is obtained
2)Prepared
statement
3)Delete
query
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