Value Object Pattern

1
Value Object Pattern

• by
• Mintao Si (mtsi06_at_yahoo.com)

2
Content

• Problem
• Forces
• Solution
• Structure
• Strategy
• Consequences

3
Problem

• Context Application clients need to exchange
  data with enterprise beans.
• J2EE enterprise beans include session beans and
  entity beans.
• Session beans may provide coarse-grained service
  methods which may return data to the client. In
  such cases, the client must invoke the session
  bean's get methods multiple times until the
  client obtains values for all the attribute
  values.
• An entity bean exposes the values of its
  attributes by providing an getter for each
  attribute. When a client needs the data values
  from an entity bean, it may invoke the entity
  bean's get methods multiple times until the
  client obtains data for every attribute that it
  needs.
• Every such method call made to the enterprise
  bean is potentially remote and multiple remote
  method invocation may significantly degrade the
  application performance.

4
Problem

• Clients make numerous remote procedure calls to
  obtain required data

Enterprise bean
Request Attribute A
Attribute A,B,C,D getA() getB() getC() getD()
Request Attribute B
client
Request Attribute C
Request Attribute D
5
Forces

• J2EE applications implement business components
  as enterprise bean components. All access to an
  enterprise bean is performed via remote
  interfaces to the bean. Every call to an
  enterprise bean is potentially a remote method
  call with network overhead.
• Typically, applications have a greater frequency
  of read transactions than update transactions.
  The client requires the data from the business
  tier for presentation, display, and other
  read-only types of processing.
• The client usually requires more than one
  attribute value of an enterprise bean. Thus, the
  client may invoke multiple remote calls to obtain
  the required data.
• The number of calls made by the client to the
  enterprise bean impacts network performance.
  Chattier applications-those with increased
  traffic between client and server tiers-often
  degrade network performance.

6
Solution

• Use a Value Object to encapsulate the business
  data. When a client requests an enterprise bean
  for business data, the enterprise bean can
  construct a Value Object, populate it with its
  attribute values, and pass it by value to the
  client.
• Using value objects can reduce remote procedure
  call and therefore reduce network overhead.
• When an enterprise bean uses a value object, the
  client makes a single remote method invocation to
  the enterprise bean to request the value object
  instead of many remote method calls to get
  individual attribute values one at a time.
• The client receives a value object and access
  the attribute values locally.

7
Structure
8
Strcuture

• Client
• This represents the client of the enterprise
  bean.
• BusinessObject
• The BusinessObject represents a role in this
  pattern that can be fulfilled by a session bean
  or an entity bean. The BusinessObject is
  responsible for creating the value object and
  returning the ValueObject to the client. The
  BusinessObject receives the data request from the
  client and creates a new ValueObject.
• ValueObject
• The ValueObject is an arbitrary Java object. The
  ValueObject may provide a constructor that
  accepts all the required attributes to create the
  value object. The constructor may accept all
  entity bean attribute values that the value
  object is designed to hold. It is a design choice
  as to whether the ValueObject attributes are
  private and accessed via getters, or all the
  attributes are made public. Normally, there is no
  setter in a ValueObject and it is not modifiable
  after its creation.

9
Strcuture

• public class ContactVO implements
  java.io.Serializable
• // public memberspublic String firstName
  public String lastName public String address
• // constructor accepting all valuespublic
  ContactVO(String firstName, String lastName,
  String address)init(firstName, lastName,
  address)
• // method to set all the valuespublic void
  init(String firstName, String lastName, String
  address) this.firstName firstName
  this.lastName lastName this.address
  address

10
Interaction
11
Strategies

• Updateable Value Object
• can carry the changes required by the client
  back to the entity.
• Multiple Value Objects
• can produce different value objects depending on
  the client request.
• Entity Inherits Value Object (for entity beans
  only)
• use inheritance, since the entity bean
  attributes and the value object attributes are
  identical.
• Value Objects Factory (for entity beans only)
• create value objects on demand using reflection

12
Updatable Value Object
13
Updatable Value Object
14
Multiple Value Objects
15
Multiple Value Objects
16
Entity Inherits Value Object
17
Entity Inherits Value Object
18
Entity Inherits Value Object

• public class ContactVO implements
  java.io.Serializable
• // public memberspublic String firstName
  public String lastName public String address
• // create a new value object public ContactVO
  getData() return new ContactVO(this)
• public class ContactEntity extends ContactVO
  implements javax.ejb.EntityBean
• ...
• // the client calls the getData method//
  getData() is inherited from the Value Object...

19
Value Objects Factory
20
Value Objects Factory
21
Consequences

• Simplifies Entity Bean and Remote Interface
• Reduces Network Traffic
• Update Propagation and Stale Value Objects
• Synchronization and Version Control
• Reduced Code duplication
• Number of calls vs. amount of data shipped
• Concurrent Access and Transactions

22
Related patterns

• Session Façade
• Value Object Assembler
• Value List Handler
• Aggregate Entity

23
Thats all folks!

• ?????