Download EJB Transactions

EJB Transactions
Objectives
In this lesson, you will learn about:
•
•
•
Identify need of EJB transactions
Identify different types of EJB transactions
Create EJB applications using different types of transactions
J2EE Server Components
Lesson 4A / Slide 1 of 28
EJB Transactions
Pre-assessment Questions
1.
Which expression of EJB QL is used to find whether the value of an
expression is within a specified range or not?
a.
Path
b.
BETWEEN
c.
IN
d.
LIKE
J2EE Server Components
Lesson 4A / Slide 2 of 28
EJB Transactions
Pre-assessment Questions (Contd.)
2.
What is the return type of the LIKE expression of EJB QL?
a.
boolean
b.
int
c.
String
d.
char
3.
Which symbol is used to specify zero or more characters in the LIKE
expression of EJB QL query to match the sequence of characters?
a.
?
b.
_(underscore)
c.
%
d. #
J2EE Server Components
Lesson 4A / Slide 3 of 28
EJB Transactions
Pre-assessment Questions (Contd.)
4.
Which symbol is used to write comment in EJB QL?
a.
//
b.
/*
c.
/
d.
Cannot write comment in EJB QL.
5.
Which BNF symbol specifies the exclusive OR operation between two
constructs?
a.
::=:
b.
|:
c.
*:
d.
{..}:
J2EE Server Components
Lesson 4A / Slide 4 of 28
EJB Transactions
Solutions to Pre-assessment
Questions
1.
2.
3.
4.
5.
b. BETWEEN
a. boolean
c. %
d. Cannot write comment in EJB QL.
b. |:
J2EE Server Components
Lesson 4A / Slide 5 of 28
EJB Transactions
Overview of EJB Transactions
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A transaction:
• Is a single unit of work that consists of one or more operations that are
interconnected. This means that each operation in a transaction must
execute successfully in order for the transaction to complete.
• Is used by an enterprise bean to maintain the accuracy and consistency of
the information in a database.
• Enables multiple clients to access a database without compromising the
consistency and integrity of data.
J2EE Server Components
Lesson 4A / Slide 6 of 28
EJB Transactions
Overview of EJB Transactions (Contd.)
•
Importance of Transactions
• Transactions ensure the regular exchange of consistent data such that all
parties involved in the transaction maintain the same information.
• Enterprise bean applications support flat transactions only. The following
figure shows a flat transaction:
J2EE Server Components
Lesson 4A / Slide 7 of 28
EJB Transactions
Overview of EJB Transactions (Contd.)
•
The functions of transactions in real world applications are:
• Maintain consistency of data in business operations in case of network
or system failure.
• Maintain consistency and integrity of data in business operations
executed by multiple users, simultaneously.
• Control the read or write access to a shared data set.
J2EE Server Components
Lesson 4A / Slide 8 of 28
EJB Transactions
Overview of EJB Transactions (Contd.)
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ACID Properties:
• Help to maintain consistency of the data used in transaction operations.
• ACID properties of a transaction are:
• Atomicity: Implies that all the operations in a transaction must
succeed or fail as a group.
• Consistency: Ensures that either the transaction completes
successfully, leaving the system in an altered state of consistency or
the transaction fails, leaving the state in its original state of
consistency.
• Isolation: Allows multiple transactions to read from or write to a
database, one at a time.
• Durability: Ensures that data loss does not occur when a network or a
system failure occurs.
J2EE Server Components
Lesson 4A / Slide 9 of 28
EJB Transactions
Overview of EJB Transactions (Contd.)
•
Using Transactions in EJB
• A transaction can be demarcated:
• Programmatically: You need to include the code specifying a
transaction’s boundaries in the bean. You have to explicitly issue a
begin statement and a commit or rollback statement.
• Declaratively: EJB Container is responsible for starting and ending
a transaction. EJB Container issues a begin statement to start a
transaction.
• In programmatic transactions, a transaction ends when all its methods
execute a commit or rollback statement.
• You need to define when a transaction should start, and when it should
end.
• In declarative transactions, EJB container is responsible for starting and
ending a transaction.
J2EE Server Components
Lesson 4A / Slide 10 of 28
EJB Transactions
Overview of EJB Transactions (Contd.)
•
Types of Transactions
• In an enterprise bean application, transactions are managed either by
EJB container or by the enterprise bean methods themselves.
• Depending on the bean management method they deploy,
transactions are of two types:
• Container-managed transaction: Uses transaction attributes to
specify the methods that need to be part of a transaction.
• Bean-managed transactions: Uses Java Database Connectivity
(JDBC) API and Java Transaction API (JTA) to implement
transactions in an enterprise bean.
• You can use only one type of transaction for all the methods in an
enterprise bean.
• An enterprise bean uses the deployment descriptor tag,
<transaction-type>, to specify the transaction type being used by
the bean.
J2EE Server Components
Lesson 4A / Slide 11 of 28
EJB Transactions
Overview of EJB Transactions (Contd.)
•
Transaction Attributes:
• Specify which methods can be part of a transaction and how to control
their execution.
• The various transaction attributes are:
• Required: Indicates that the bean method needs to be
executed within a transaction.
• RequiresNew: Specifies that a new transaction must start every
time the specified bean method starts execution.
• Mandatory: Specifies that a bean method must always be part
of an existing transaction.
• Supports: Specifies that it is not mandatory for a bean method
to be part of a transaction.
• NotSupported: Specifies that a bean method should not be part
of a transaction.
• Never: Specifies that a bean method should not be called in the
context of an existing transaction.
J2EE Server Components
Lesson 4A / Slide 12 of 28
EJB Transactions
Overview of EJB Transactions (Contd.)
•
Container-Managed Transactions
• In this type of transactions, EJB Container:
• Handles all method invocation in a transaction.
• Starts the transaction as soon as a bean method starts executing.
• Commits or aborts the transaction just before the bean method
completes execution.
• The transaction attributes in a container-managed transaction define
which methods are to be associated with a transaction.
• The advantage of using a container-managed transaction is that a bean
method is free from the complexities of managing a transaction.
• When an error occurs in container-managed transaction’s method, the
transaction is rolled back leaving the database in its original state of
consistency.
J2EE Server Components
Lesson 4A / Slide 13 of 28
EJB Transactions
Overview of EJB Transactions (Contd.)
•
Bean-Managed Transactions
• In a bean-managed transaction, a bean method contains the code to
control transactions.
• You can declare a block of code within a bean method to be part of a
transaction.
• You can only implement one bean-managed transaction at a time.
• A bean-managed transaction begins with the execution of the
UserTransaction.begin() method and ends with the execution of the
UserTransaction.commit() method.
•
•
In a stateful session bean, a bean-managed transaction facilitates
maintaining the transactional state across several method calls.
You can use a bean-managed transaction to support compensating
transactions, which can be rolled back even after it is committed.
J2EE Server Components
Lesson 4A / Slide 14 of 28
EJB Transactions
Overview of EJB Transactions (Contd.)
•
JDBC Transactions
• JDBC enables you to implement a bean-managed transaction.
• The DBMS transaction manager controls the JDBC transactions defined
in bean methods.
• The javax.sql.Connection interface declares the transaction methods
used in JDBC transactions.
• A bean method invokes the commit() or rollback() method of the
javax.sql.Connection interface to commit or rollback a JDBC
transaction.
• Bean methods using JDBC transactions invoke the setAutoCommit()
method of the javax.sql.Connection interface. The setAutoCommit()
method notifies the DBMS transaction manager to disable the auto
commit property for every SQL statement in bean methods.
J2EE Server Components
Lesson 4A / Slide 15 of 28
EJB Transactions
Overview of EJB Transactions (Contd.)
•
JTA Transactions
• J2EE transaction manager enables you to use JTA for controlling
transaction boundaries in a bean-managed transaction.
• JTA transactions use the javax.transaction.UserTransaction
interface to programmatically control transactions.
• The getUserTransaction() method returns a reference of the
javax.transaction.UserTransaction interface.
• The methods in the javax.transaction.UserTransaction interface
are:
• begin()
• commit()
• rollback()
• setRollBackOnly()
• setTransactionTimeout(int)
• getStatus()
J2EE Server Components
Lesson 4A / Slide 16 of 28
EJB Transactions
Overview of EJB Transactions (Contd.)
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•
JTA enables you to declare a business method for performing operations
in a transaction.
You need to adhere to the following rules in implementing the
javax.transaction.UserTransaction interface:
•
•
•
Transactions in an entity bean do not use the
javax.transaction.UserTransaction interface.
Transactions in a stateless session bean method should end before
the method finishes execution. Failure in ending a transaction leads
to transaction rollback and the exceptions, RemoteException or
EJBException, are thrown.
Transactions in a message-driven bean should end before the
onMessage() method finishes execution.
J2EE Server Components
Lesson 4A / Slide 17 of 28
EJB Transactions
Overview of EJB Transactions (Contd.)
•
Responsibilities of the Container Provider and the Bean Provider in
Transactions
• EJB container provider and the bean provider are responsible for
controlling transactions in an enterprise bean.
• EJB container performs the following operations if a method in a
stateless session bean ends without completing the transaction:
• Rolls back the transaction.
• Generates an application error.
• Throws the exceptions, java.rmi.RemoteException or
javax.ejb.EJBException, depending on whether the client is
remote or local, respectively.
• Removes the instance of the session bean that started the
transaction and returned before the completion of the transaction.
J2EE Server Components
Lesson 4A / Slide 18 of 28
EJB Transactions
Overview of EJB Transactions (Contd.)
•
•
•
EJB Container performs the following operations if the method returns
without committing the transaction:
• Generates an application error.
• Rolls back the transaction started by the method.
• Removes the instance of the message-driven bean that started the
transaction and returned without its completion.
EJB container throws the exception,
java.lang.IllegalStateException, if an instance of a bean-managed
transaction enterprise bean calls the methods, setRollbackOnly() or
getRollbackOnly().
EJB container throws the exception,
javax.transaction.NotSupportedException, if an instance of a beanmanaged transaction enterprise bean starts a new transaction using the
begin() method without ending the previously started transaction.
J2EE Server Components
Lesson 4A / Slide 19 of 28
EJB Transactions
Overview of EJB Transactions (Contd.)
•
Responsibilities of EJB container in a Container-Managed Transaction
• An instance of a container-managed transaction enterprise bean
invokes the EJBContext.setRollbackOnly() method to mark a
transaction for rollback.
• EJB container performs the following tasks if the instance that calls
the method, EJBContext.setRollbackOnly(), contains the
transaction attributes, Required, RequiresNew, or Mandatory:
•
•
Ensures that the transaction should not commit and marks
the transaction for rollback.
Checks if the enterprise bean instance has invoked the
setRollbackOnly() method if EJB container starts a
transaction before the business method is dispatched to the
instance. When the business method completes execution,
EJB container rollbacks the transaction and passes the result
to the client.
J2EE Server Components
Lesson 4A / Slide 20 of 28
EJB Transactions
Overview of EJB Transactions (Contd.)
•
•
EJB Container throws the java.lang.IllegalStateException if
the method that started the transaction calls the
EJBContext.setRollbackOnly() method and has the transaction
attributes, Supports, NotSupported, or Never (for messagedriven bean, NotSupported only) .
The java.lang.IllegalStateException is also thrown if an
instance that has the container-managed transaction calls the
getUserTransaction() method of the EJBContext interface.
J2EE Server Components
Lesson 4A / Slide 21 of 28
EJB Transactions
Overview of EJB Transactions (Contd.)
•
Responsibilities Of the Bean Provider
• The bean provider controls the implementation of bean-managed
transactions. The bean provider performs the following functions:
• Defines the type of transaction for a session bean.
• Specifies the transaction attributes when creating the
deployment descriptor. In a container-managed transaction,
the application assembler can modify the transaction
attributes specified by the bean provider in the deployment
descriptor
• Defines the boundaries of a transaction.
• Enables one method to start many transactions in a beanmanaged transaction.
• Enables a JTA transaction to invoke a method in a stateful
session bean even if the method has closed the connection to
the database.
J2EE Server Components
Lesson 4A / Slide 22 of 28
EJB Transactions
Demonstration-Implementing JTA
Bean-Managed Transactions
•
Problem Statement
• Nancy is developing one of the modules in the online banking
application that will allow customers to deposit money. The
application should use a database to store customer information
and the deposited amount. The application also needs to use JTA
transaction to ensure data integrity.
J2EE Server Components
Lesson 4A / Slide 23 of 28
EJB Transactions
Demonstration-Implementing JTA
Bean-Managed Transactions
(Contd.)
•
Solution
•
To solve
1.
2.
3.
4.
5.
6.
7.
8.
the preceding problem, perform the following tasks:
Create the stateful session bean home interface.
Create the session bean remote interface.
Create the session bean class.
Create the Web client.
Package the session bean.
Package the Web client.
Deploy the application.
Test the application.
J2EE Server Components
Lesson 4A / Slide 24 of 28
EJB Transactions
Demonstration-Implementing
Container-Managed Transactions in
CMP Entity Beans
•
Problem Statement
•
Chris is developing the module in the online banking application
that will allow customers to withdraw funds. Every account
needs to maintain a minimum amount of $1000. Chris needs to
use a CMP entity bean in this application and ensure that
minimum balance in an account is maintained.
J2EE Server Components
Lesson 4A / Slide 25 of 28
EJB Transactions
Demonstration-Implementing
Container-Managed Transactions in
CMP Entity Beans (Contd.)
•
Solution
•
To solve
1.
2.
3.
4.
5.
6.
7.
8.
the preceding problem, perform the following tasks:
Create the CMP entity bean home interface.
Create the CMP entity bean remote interface.
Create the CMP entity bean class.
Create the Web client.
Package the session bean.
Package the Web client.
Deploy the application.
Test the application.
J2EE Server Components
Lesson 4A / Slide 26 of 28
EJB Transactions
Summary
In this lesson, you learned:
•
•
•
•
•
•
An enterprise bean uses transactions to maintain consistency of data in a
database.
All operations in a transaction need to complete successfully in order to make
the transaction successful.
A transaction needs to exhibit four characteristics: Atomicity, Consistency,
Isolation, and Durability.
A transaction can either be container-managed or bean-managed.
In a bean-managed transaction, the bean contains the code to specify the
transaction boundaries.
In a container-managed transaction, EJB container is responsible for
demarcating transaction boundaries.
J2EE Server Components
Lesson 4A / Slide 27 of 28
EJB Transactions
Summary (Contd.)
•
•
•
•
•
•
EJB container uses the Required, RequiresNew, Mandatory, Supports,
NotSupported, and Never transaction attributes to specify which methods
can be included in a transaction.
An advantage of using container-managed transaction is that it frees a bean
method from the complexities of managing a transaction. It also helps in
reducing the coding time.
The execution of the UserTransaction.begin() method marks the start of
a bean-managed transaction and the execution of the
UserTransaction.commit() method marks the end of a transaction.
A bean-managed transaction is implemented using JDBC and JTA.
JDBC transactions use methods of the javax.sql.Connection interface to
implement a transaction.
The methods of javax.transaction.UserTransaction interface are used in
JTA transactions to programmatically control transaction boundaries.
J2EE Server Components
Lesson 4A / Slide 28 of 28