Service Locator Pattern

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Service Locator Pattern

• Hanh Nguyen

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Overview

• Context
• Problem
• Forces
• Solution
• Strategy
• Consequences
• Demo

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Context

• Service lookup and creation involves complex
  interfaces and network operations

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Problem

• J2EE clients interact with EJB and JMS.
• Clients must either locate these components or
  create a new ones
• Clients use the common JNDI to locate those
  components

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Forces

• The context factories are difference from vendor
  to vendor
• Lookup and creation of service components could
  be complex and may be used repeatedly and
  resource-intensive

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Solution

• Use Service Locator object to abstract all JNDI
  usage and to hide the complexities of initial
  context creation
• Multiple clients can reuse the Service Locator
  object.

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Structure
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Participants and Responsibilities
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Sample code - Service Locator

• public class ServiceLocator
• private ServiceLocator() context new
  InitialContext()
• public static ServiceLocator getInstance()
• if (me null) me new ServiceLocator()
• return me
• public EJBHome getHome(String name, Class clazz)
  
• Object objref context.lookup(name)
• EJBHome home PortableRemoteObject.narrow(objre
  f,clazz)
• return home

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Sample code - Client

• public class ServiceLocatorTester
• public static void main( String args )
  ServiceLocator serviceLocator
  ServiceLocator.getInstance()

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Strategy - EJB Service Locator
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Strategy - EJB Service Locator
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Strategy - JMS Queue Service Locator
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Strategy - JMS Queue Service Locator
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Strategy - JMS Topic Service Locator Strategy
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Strategy - JMS Topic Service Locator Strategy
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Consequences

• Abstracts Complexity
• Provides Uniform Service Access to Clients
• Facilitates Adding New Business Components
• Improves Network Performance
• Improves Client Performance by Caching

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Demo

• Encryption Decryption Service
• Using Service Locator pattern to implement load
  balancing and fail over.

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Crypto Service Diagram