Enterprise Java Beans - PowerPoint PPT Presentation

Loading...

PPT – Enterprise Java Beans PowerPoint presentation | free to view - id: 1d4d6e-ZDc1Z



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

Enterprise Java Beans

Description:

Business methods. Code a home interface. Finder methods. Home ... Bean's business methods. Code the local home interface. Life cycle. Finder methods. 11/8/09 ... – PowerPoint PPT presentation

Number of Views:78
Avg rating:3.0/5.0
Slides: 101
Provided by: raCrem
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Enterprise Java Beans


1
(No Transcript)
2
Enterprise Java Beans
  • Introduction
  • Application Server
  • Java 2 Enterprise Edition
  • What is an Enterprise Bean ?
  • EJB Properties
  • EJB Overview
  • Deployment Phase
  • Type of beans
  • Client access with interfaces
  • Remote access
  • Local Access

3
Enterprise Java Beans
  • Contents of an Enterprise Bean
  • EJB Example
  • EJB vs MTS
  • A few EJB implementations
  • Whats new in EJB 2.0
  • Bibliography

4
Introduction
  • Enterprise Java Beans ( EJB ) is
  • a middleware component model for Java and CORBA
  • a specification for creating server-side,
    scalable, transactional, multi-user and secure
    enterprise-level applications
  • Presented by Sun in the 1999, they are easier
    than other technologies as RMI or Corba

5
Introduction
  • This is the three level structure for Application
    Server

6
Applicaton Server
  • Presentation
  • HTML Application
  • Java Application
  • Business Logic
  • Data Access

7
Presentation
  • HTML
  • Generated server-side HTML
  • Runs on any Web browser
  • Less client-side power
  • Java
  • Required Java virtual Machine
  • More client side power
  • Runned on a page
  • Launched from a browser or a standalone
    application

8
Business Logic
  • Implements the logic of the application defining
    all the function that may be used from a client
  • Change Business Rules Easily
  • Re-use components
  • Make complex applications manageable

9
Data Access
  • Utility to access external datas such as Database
    or other Web component

10
J2EE Application Server
  • Java 2 Enterprise Edition standardizes interfaces
    for Application Server components

11
What is an Enterprise Bean ?
  • Is a server side component written in Java
    Language
  • Industry standard distribuited component model
  • Incorporates the business logic of an application
    ( the code that implements the purpose of the
    application)

12
EJB Properties
  • Bean writers need not write
  • Remote access Protocols
  • Transactional Behaviour
  • Threads
  • Security
  • State Management
  • Object life cycle
  • Resource pooling
  • Persistence

13
EJB Overview
14
Deployment Phase
15
Deployment Phase
16
When to use Enterprise bean
  • The application must be scalable.It will run on
    different machine and their location will remain
    transparent to the client
  • Transaction requirement
  • The application will have lot of different type
    of clients

17
Type of beans
  • Session Bean
  • Entity Bean
  • Message Driven Bean

18
Session Bean
  • Represents a single client inside the server
  • The client calls the session bean to invoke
    methods of an application on the server
  • Perform works for its client, hiding the
    complexity of interaction with other objects in
    the server
  • Is not shared
  • Is not persistent
  • When the client stops the session,the bean can be
    assigned to another client from the server

19
Session Bean
  • Stateful session bean
  • Stateless session bean

20
Stateful Session Bean
  • Contains the state of a single client session
  • Information on the client
  • On method called
  • Return values
  • This state is called conversational state and is
    not retained when the session ends, also if the
    client not removes the bean

21
Stateless Session Bean
  • Not maintain a conversational state for a
    particular client
  • Contains values only for the duration of the
    single invocation
  • Except during method invocation, all instances of
    stateless session bean are equivalent

22
Entity Bean
  • Represents a business object in a persistent
    storage mechanism such as a relational database
  • Usually is a table in the database and each
    instance of that entity bean is a row in that
    table
  • Properties
  • Persistent
  • Allow shared access
  • Have primary key
  • Have relationship with other entity beans.

23
Entity Bean persistent
  • Bean managed persistence
  • Container managed persistence

24
Bean managed persistence
  • Who write the beans code must access the
    database and save his own data

25
Container managed persistence
  • The container save the data
  • There is no code in the bean for access the
    database
  • The container handles all database access
    required for the bean
  • Links between beans are created using a structure
    called abstract schema

26
Entity beans shared access
  • Entity beans can be used by different clients
  • Its important that they work whithin
    transactions
  • The EJB container provides transaction management
  • The transactions attribute are specified in the
    beans deployment description

27
Entity beans primary key
  • Each entity bean has a unique object identifier
    like a key in a database table

28
Entity beans relationship
  • Container managed persistent
  • The container performs all the operation to
    create relationship
  • Bean managed persistent
  • The code to perform relations must be written in
    the bean

29
Message Driven bean
  • Allows applications to process messages
    asynchronously
  • The messages may be sent by
  • An application client
  • Another enterprise bean
  • A Web component

30
Message Driven bean
  • Retain no data or conversational state for a
    specific client
  • All instances are equivalent, allowing the EJB
    container to assign a message to any
    message-driven bean instance. The container can
    pool these instances to allow streams of messages
    to be processed concurrently
  • Can process messages from multiple clients

31
Message Driven bean
  • A client cant access directly to a message
    driven bean
  • When a message arrive, the container gives it to
    a message driven bean
  • The bean process the message

32
Client access with interfaces
  • A client may access a session or an entity bean
    only through the methods defined in the bean's
    interfaces
  • They define the client's view of a bean
  • Types of access
  • Remote access
  • Local access

33
Remote access
  • A remote client of an enterprise bean has the
    following traits
  • It may run on a different machine and a different
    Java virtual machine than the enterprise bean it
    accesses (It is not required to run on a
    different JVM )
  • It can be a Web component
  • It can be another enterprise bean

34
Remote access
  • To create an enterprise bean with remote access,
    you must
  • Code a remote interface
  • Business methods
  • Code a home interface
  • Finder methods
  • Home methods

35
Remote access example
36
Local access
  • A local client has these characteristics
  • It must run in the same JVM as the enterprise
    bean it accesses
  • It may be a Web component or another enterprise
    bean
  • To the local client, the location of the
    enterprise bean it accesses is not transparent
  • It is often an entity bean that has a
    container-managed relationship with another
    entity bean

37
Local access
  • To create an enterprise bean with local access,
    you must
  • Code the local interface
  • Bean's business methods
  • Code the local home interface
  • Life cycle
  • Finder methods

38
Local interfaces
  • If an entity bean is the target of a container
    managed relationship it MUST have local
    interfaces

39
Contents of an Enterprise Bean
  • Deployment descriptor
  • Persistence type
  • Transaction attribute
  • Enterprise bean class
  • Interfaces
  • Helper classes
  • Exception
  • Utility classes

40
EJB Example
  • The OnLine Bank
  • We will take a not completed system to give an
    idea to how choose if a component is an entity,
    session or message driven bean.

41
EJB Example
 
42
EJB Example
  • The example has three component
  • Services what the client can do in the system
    such as see the foreign currency , listed shares
    or make operations on his hown account.
  • Accounts a database containing the accounts of
    all the clients of the bank with information
    about credit,debit,access etc..
  • Security is a subsystem that receives all the
    alarm caused from wrong access and performs
    action about the situation
  • ( calls police and stops operation of that
    client keeping information about him )

43
EJB Example
  • In this example is easy to create an EJB
    structure.
  • Client will have a web page at client side to
    insert values and connect the system.This will be
    done using JSP ( Java Servlet Pages )
  • Services will be a Statefull Session Bean and it
    will be different for each client connecting the
    system mantaining data about the client
    connected.
  • Accounts will be formed by an Entity Bean for
    each account in the system with a code-account as
    primary key.
  • Security will be a Message driven bean and will
    be called only from container if some operation
    are abnormal for result or the autentification
    for the same client fails too much times.

44
EJB vs MTS
  • Microsoft Transaction Server is based on the
    Component Object Model (COM) which is the
    middleware component model for Windows NT
  • MTS can be defined as a component-based
    programming model

45
EJB vs MTS Analogies
  • Implement business logic for Application Server
    components
  • Have a Server and a container ( for MTS called
    MTS Executive )
  • Similar architecture in both models
  • A client invokes wrapped method

46
EJB vs MTS Difference
  • EJB
  • Component instance are pooled
  • Dont support heterogeneous transactions
  • Portability accross multiple platforms using Java
    platform
  • MTS
  • Component is not created until the call from a
    client reaches the container
  • Support heterogeneous transactions
  • Portability only on Windows NT

47
EJB vs MTS Difference
  • EJB
  • Invoked by clients using RMI
  • Has both persistent and non-persistent components
  • MTS
  • Invoked by clients using DCOM or through local
    COM calls
  • Components are not persistent, even though they
    may contain information

48
A few EJB implementations
  • WebLogic
  • Bluestone
  • Novera
  • Persistence
  • Oracle AS
  • Oracle8i

49
Whats new in EJB 2.0
  • Released On April 26, 2001
  • Integration with JavaTM Message Service (JMS) --
    Asynchronous Capabilities Streamline Systems
  • Send asynchronous messages via the JMS API
  • Container-Managed Persistence (CMP) --
    Simplifying and Expediting Application
    Development
  • Used to isolate the application developer from
    the physical database schema
  • Introduces for the first time a portable query
    language, based on the abstract schema

50
Whats new in EJB 2.0
  • Local Interfaces -- Streamlining Calls Between
    Local Beans
  • 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
  • Inter-Server Interoperability -- Enabling
    Heterogeneous Environments
  • Takes the benefit of cross-server application
    portability
  • Able to deploy the EJB technology-based
    application across a heterogeneous environment
    mixing application servers from different vendors

51
Bibliography
  • The J2EE Tutorial
  • http//java.sun.com/j2ee/tutorial/1_3-fcs/doc/EJBC
    oncepts.html
  • Meeting about Application servers
  • http//www.phxjug.org/meetings/silverstream/sld001
    .htm
  • Developing Enterprise components
  • http//spectral.mscs.mu.edu/EJB20001113/index.html
  • A detailed Comparison of EJB MTS models
  • http//members.tripod.com/gsraj/misc/ejbmts/ejbmts
    comp.html

52
Bibliography
  • What's new in the Enterprise JavaBeansTM 2.0
    Specification?
  • http//java.sun.com/products/ejb/2.0.html
  • Introduction to Enterprise JavaBeans
  • http//cosmos.inesc.pt/a01/javacourses/ejb/
  • Programming WebLogic Enterprise JavaBeans
  • http//e-docs.bea.com/wls/docs61/ejb/index.html

53
The MTS architecture
  • Is made up of
  • The MTS Executive (mtxex.dll)
  • The Factory Wrappers and Context Wrappers for
    each component
  • The MTS Server Component
  • MTS clients
  • Auxiliary systems like
  • COM runtime services,
  • Service Control Manager (SCM)
  • The Microsoft Distributed Transaction Coordinator
    (MS-DTC)
  • The Microsoft Message Queue (MSMQ)
  • The COM-Transaction Integrator (COM-TI)

54
The MTS architecture
55
The EJB architecture
  • Consists of
  • An EJB server
  • EJB containers that run within the server
  • Home objects
  • Remote EJBObjects
  • Enterprise Beans
  • EJB clients
  • Auxiliary systems like
  • Java Naming and Directory Interface (JNDI)
  • Java Transaction Service (JTS)
  • Security services

56
The EJB architecture
57
Stateful session beans life cycle
  • The client invoke the create method
  • The EJB container
  • Instantiates the bean
  • Invokes the setSessionContext
  • Invokes ejbCreate
  • The bean is ready

58
Stateful session beans life cycle
  • While in the ready state
  • EJB container may passivate the bean moving it
    from memory to secondary storage
  • A client may invoke a business method
  • EJB container may activate a bean,moving it back
    to the ready stage, and then calls the bean's
    ejbActivate method
  • A client may invoke the remove method and the
    container calls the bean's ejbRemove method

59
Stateful session beans life cycle
60
Stateless session beans life cycle
  • The client invoke the create method
  • The EJB container
  • Instantiates the bean
  • Invokes the setSessionContext
  • Invokes ejbCreate
  • The bean is ready

61
Stateless session beans life cycle
  • While in the ready state
  • A client may invoke a business method
  • A client may invoke the remove method and the
    container calls the bean's ejbRemove method
  • Its never passivate

62
Stateless session beans life cycle
63
Entity beans life cycle
  • The EJB container
  • Creates the instance
  • Calls the setEntityContext
  • The entity bean moves to a pool of available
    instances

64
Entity beans life cycle
  • While in the pool
  • Instance is not associated with any particular
    object identity
  • All instances in the pool are identical
  • EJB container may assign an identity to an
    instance when moving it to the ready stage
    invoking the ejbActivate method
  • A client may invoke the create method
  • EJB container calls ejbCreate and ejbPostCreate
  • EJB container may remove the instance invoking
    unsetEntityContext

65
Entity beans life cycle
  • While in the ready state
  • A client may invoke entity bean's business
    methods
  • A client may invoke the remove method
  • EJB container calls the ejbRemove method
  • EJB container may invoke the ejbPassivate method

66
Entity beans life cycle
67
Message driven beans life cycle
  • EJB container creates a pool of message-driven
    bean instances
  • For each instance, the EJB container instantiates
    the bean
  • It calls the setMessageDrivenContext
  • It calls the instance's ejbCreate
  • Like a stateless session bean,its never
    passivated, It has only two states
  • Nonexistent
  • Ready to receive messages.

68
Message driven beans life cycle
  • While in the ready state
  • EJB container may call onMessage
  • EJB container may call the ejbRemove

69
Message driven beans life cycle
70
Abstract schema
  • Part of an entity bean's deployment descriptor
  • Defines the bean's persistent fields and
    relationships.The term abstract distinguishes
    this schema from the physical schema of the
    underlying data store
  • You specify the name of an abstract schema in the
    deployment descriptor

71
Example of Abstract schema
72
Abstract schema
  • Persistent fields
  • Are stored in the underlying data store
  • Constitute the state of the bean. At runtime, the
    EJB container automatically synchronizes this
    state with the database
  • During deployment, the container
  • Maps the entity bean to a database table
  • Maps the persistent fields to the table's columns

73
Abstract schema
  • Relationship fields
  • Its like a foreign key in a database table.It
    identifies a related bean
  • Like a persistent field, a relationship field is
    virtual and is defined in the enterprise bean
    class with access methods
  • Unlike a persistent field, a relationship field
    does not represent the bean's state

74
Abstract schema
  • Multiplicity in Container-Managed Relationships
  • One-to-one Each entity bean instance is related
    to a single instance of another entity bean
  • One-to-many An entity bean instance may be
    related to multiple instances of the other entity
    bean
  • Many-to-one Multiple instances of an entity bean
    may be related to a single instance of the other
    entity bean
  • Many-to-many The entity bean instances may be
    related to multiple instances of each other

75
Abstract schema
  • Direction in Container-Managed Relationships
  • Bidirectional relationship each entity bean has
    a relationship field that refers to the other
    bean. Through the relationship field, an entity
    bean's code can access its related object
  • Unidirectional relationship only one entity bean
    has a relationship field that refers to the other

76
EJB 3.0
  • This section based on
  • Mastering EJB 3.0 4th Ed

77
EJB 3.0
  • Key issues for distributed systems
  • Remote Method Invocation
  • Load Balancing
  • Transparent failover
  • Back-end integration to legacy systems
  • Transactions
  • Clustering (state replication across servers)
  • Dynamic redeployment (upgrade while running)

78
EJB 3.0
  • More key issues
  • Clean shutdown
  • Logging auditing
  • Systems management
  • Threading
  • Message-oriented middleware
  • Component lifecycle
  • Resource pooling

79
EJB 3.0
  • Yet more issues
  • Security
  • Caching
  • Etc., etc.

80
EJB 3.0
  • All of these can be thought of as middleware
    services
  • Developer of distributed app shouldnt have to
    worry about them
  • Should concentrate on business logic
  • Much too expensive to build from scratch
  • Distributed app should be portable across
    middleware service providers

81
EJB 3.0
  • EJB spec defines standard interfaces between
    distributed components their containers

82
EJB 3.0
  • Advantages
  • Industry standard
  • Vendors design containers to EJB specs
  • Portability possible across containers
  • RAD capable because services provided by
    container

83
EJB 3.0
  • Whats an EJB?
  • Server-side component encapsulating application
    functionality
  • Business logic
  • DB access
  • Integrate with other legacy systems
  • Serve multiple clients
  • Browser
  • Desktop apps
  • Other EJBs
  • Web app components (e.g., Servlets)
  • Web Service clients

84
EJB 3.0
  • How do they work?
  • EJB can be located anywhere, usually on another
    machine
  • Use RMI-IIOP for remote invocation of methods (P.
    15)
  • Location transparency
  • Client thinks remot EJB is local
  • Run inside EJB container
  • Application servers

85
EJB 3.0
  • Who makes containers?
  • Most of the usual enterprise suspects
  • BEA, IBM, Red Hat (JBOSS), Sun, Oracle
  • Closely related to web services
  • P. 29

86
EJB 3.0
  • EJB 2.1 was NASTY!!
  • HelloWorld EJB 2.1 (pp. 40-49)
  • Many disappointed enterprise developers
  • Vastly simplified in EJB 3.0
  • HelloWorld EJB 3.0 (pp. 83-85)
  • Many once burned twice shy developers
  • Suns dilemma
  • If we simplify it, will they resume coding EJBs?

87
EJB 3.0
  • EJB best practices
  • For appropriate use only
  • Remoting is required
  • Distributed transactions required
  • Component security required
  • Persistence required
  • Legacy system integration
  • Scalability required

88
EJB 3.0
  • If your application components dont need to be
    distributed across servers, avoid using
    distributed components like EJBs

89
EJB 3.0
  • This section based on
  • J2EE Development Without EJB

90
EJB 3.0
  • Written by a once burned twice shy EJB
    developer
  • Observations apply to EJB 2.1 (and earlier)
    experiences
  • EJB 3.0 spec in early stages when book written

91
EJB 3.0
  • Basic thesis is EJBs.
  • Rarely necessary for web-based applications
  • Commonly overused
  • Symptom of over-engineering
  • Can obtain most of needed EJB services via other
    programming techniques using lightweight
    containers (e.g., Spring)
  • Java EE Java SE
  • Aspect-oriented programming
  • Dynamic proxies

92
EJB 3.0
  • Hes not alone
  • Many other enterprise architects and developers
    have critized EJBs since early 2000s
  • Martin Fowlers Law of Distributed Objects
  • Dont do it!!

93
EJB 3.0
  • Some criticisms
  • Too complex
  • Specifications getting more complex
  • EJB 3.0 tries to address this
  • Unit testing hard to do
  • Have to isolate app from container
  • If something broken, is it container related or
    app related?

94
EJB 3.0
  • Other technologies (AOP) get the job done more
    easily
  • Entity beans are a flop
  • EJB 3.0 doesnt upgrade entity beans
  • Left to wither on the Java EE vine
  • Persistence API tries to address this

95
EJB 3.0
  • Metadata (a la .NET) are better than descriptor
    files
  • Annotations designed to address this
  • Only truly unique service provided by EJB is
    remote access to a component
  • Java EE provides other services already
  • JNDI, JTA, JCA, resource pooling, etc.

96
EJB 3.0
  • EJBs remain best choice for apps that genuinely
    need object distribution or use IIOP protocol
  • EJBs also pretty good for apps based around
    asynchronous messaging
  • Message-drive beans pretty simple

97
EJB 3.0
  • Financial services middleware likely good place
    for EJB-driven apps
  • Argues that EJBs are declining technology will
    be legacy within 3 years
  • Doesnt think EJB 3.0 will make much of a
    difference

98
EJB 3.0
  • Advocates use of lightweight containers like
    Spring.
  • Oh btw, author is co-founder of Spring framework!
  • Bias is always an issue!

99
EJB 3.0
  • Whats an enterprise developer to do?
  • Distributed systems a holy grail of system
    architecture deployment since early 90s
  • CORBA initiative began in 91
  • Web Services are current frontier
  • IT profession still learning when how to do
    distributed systems

100
EJB 3.0
  • References
  • Master Enterprise JavaBeans 3.0, 4th Ed,
    Sriganesh et. Al., 2006
  • J2EE Development Without EJB, Johnson, 2004
About PowerShow.com