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MSaifAsifMSaifAsif
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Implementatation of the Service locator pattern
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‎pom.xml‎

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<module>visitor</module>
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<module>double-checked-locking</module>
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<module>servant</module>
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<module>service-locator</module>
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</modules>
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<build>

‎service-locator/etc/model.ucls‎

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<?xml version="1.0" encoding="UTF-8"?>
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<class-diagram version="1.1.7" icons="true" automaticImage="PNG" always-add-relationships="false" generalizations="true"
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realizations="true" associations="true" dependencies="false" nesting-relationships="true">
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<interface id="1" language="java" name="com.iluwater.Service" project="service-locator"
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file="/service-locator/src/main/java/com/iluwater/Service.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="110" y="182"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</interface>
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<class id="2" language="java" name="com.iluwater.ServiceImpl" project="service-locator"
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file="/service-locator/src/main/java/com/iluwater/ServiceImpl.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="342" y="374"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</class>
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<class id="3" language="java" name="com.iluwater.ServiceLocator" project="service-locator"
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file="/service-locator/src/main/java/com/iluwater/ServiceLocator.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="702" y="175"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</class>
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<class id="4" language="java" name="com.iluwater.ServiceCache" project="service-locator"
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file="/service-locator/src/main/java/com/iluwater/ServiceCache.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="397" y="81"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</class>
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<realization id="5">
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<end type="SOURCE" refId="2"/>
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<end type="TARGET" refId="1"/>
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</realization>
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<association id="6">
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<end type="SOURCE" refId="3" navigable="false">
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<attribute id="7" name="serviceCache">
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<position height="0" width="0" x="0" y="0"/>
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</attribute>
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<multiplicity id="8" minimum="0" maximum="1">
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<position height="0" width="0" x="0" y="0"/>
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</multiplicity>
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</end>
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<end type="TARGET" refId="4" navigable="true"/>
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<display labels="true" multiplicity="true"/>
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</association>
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<association id="9">
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<end type="SOURCE" refId="4" navigable="false">
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<attribute id="10" name="serviceCache">
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<position height="0" width="0" x="0" y="0"/>
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</attribute>
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<multiplicity id="11" minimum="0" maximum="2147483647">
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<position height="0" width="0" x="0" y="0"/>
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</multiplicity>
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</end>
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<end type="TARGET" refId="1" navigable="true"/>
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<display labels="true" multiplicity="true"/>
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</association>
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<classifier-display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</classifier-display>
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<association-display labels="true" multiplicity="true"/>
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</class-diagram>

‎service-locator/etc/service-locator.png‎

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‎service-locator/pom.xml‎

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<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<parent>
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<groupId>com.iluwatar</groupId>
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<artifactId>java-design-patterns</artifactId>
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<version>1.0-SNAPSHOT</version>
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</parent>
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<artifactId>service-locator</artifactId>
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</project>

‎service-locator/src/main/java/com/iluwater/App.java‎

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package com.iluwater;
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/**
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* Service locator pattern, used to lookup jndi services
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* and cache them for subsequent requests.
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* @author saifasif
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*
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*/
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public class App {
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public static void main(String[] args) {
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Service service = ServiceLocator.getService("jndi/serviceA");
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service.execute();
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service = ServiceLocator.getService("jndi/serviceB");
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service.execute();
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service = ServiceLocator.getService("jndi/serviceA");
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service.execute();
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service = ServiceLocator.getService("jndi/serviceA");
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service.execute();
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}
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}

‎service-locator/src/main/java/com/iluwater/InitContext.java‎

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package com.iluwater;
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/**
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* For JNDI lookup of services from the web.xml. Will match name of the service name that
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* is being requested and return a newly created service object with the name
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* @author saifasif
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*
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*/
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public class InitContext {
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/**
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* Perform the lookup based on the service name. The returned object will need to be
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* casted into a {@link Service}
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* @param serviceName
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* @return
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*/
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public Object lookup(String serviceName){
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if( serviceName.equals("jndi/serviceA") ){
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System.out.println("Looking up service A and creating new serivce for A");
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return new ServiceImpl("jndi/serviceA");
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} else if( serviceName.equals("jndi/serviceB") ){
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System.out.println("Looking up service B and creating new serivce for B");
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return new ServiceImpl("jndi/serviceB");
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} else {
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return null;
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}
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}
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}

‎service-locator/src/main/java/com/iluwater/Service.java‎

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package com.iluwater;
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/**
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* This is going to be the parent service interface which we will
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* use to create our services. All services will have a
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* <li>service name</li>
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* <li>unique id</li>
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* <li>execution work flow</li>
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* @author saifasif
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*
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*/
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public interface Service {
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/*
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* The human readable name of the service
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*/
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public String getName();
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/*
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* Unique ID of the particular service
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*/
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public int getId();
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/*
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* The workflow method that defines what this service does
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*/
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public void execute();
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}

‎service-locator/src/main/java/com/iluwater/ServiceCache.java‎

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package com.iluwater;
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import java.util.HashMap;
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import java.util.Map;
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/**
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* The service cache implementation which will cache services that are being created.
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* On first hit, the cache will be empty and thus any service that is being requested, will be
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* created fresh and then placed into the cache map. On next hit, if same service name will
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* be requested, it will be returned from the cache
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* @author saifasif
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*
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*/
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public class ServiceCache {
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private Map<String, Service> serviceCache;
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public ServiceCache() {
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serviceCache = new HashMap<String, Service>();
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}
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/**
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* Get the service from the cache. null if no service is found matching the
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* name
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* @param serviceName
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* @return {@link Service}
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*/
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public Service getService(String serviceName){
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Service cachedService = null;
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for (String serviceJndiName : serviceCache.keySet()){
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if( serviceJndiName.equals( serviceName ) ){
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cachedService = serviceCache.get(serviceJndiName);
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System.out.println("(cache call) Fetched service " + cachedService.getName() + "("+cachedService.getId()+") from cache... !");
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}
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}
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return cachedService;
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}
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/**
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* Adds the service into the cache map
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* @param newService
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*/
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public void addService(Service newService){
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serviceCache.put(newService.getName(), newService);
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}
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}

‎service-locator/src/main/java/com/iluwater/ServiceImpl.java‎

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package com.iluwater;
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/**
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* This is a single service implementation of a sample service. This is the actual
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* service that will process the request. The reference for this service is to
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* be looked upon in the JNDI server that can be set in the web.xml deployment descriptor
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* @author saifasif
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*
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*/
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public class ServiceImpl implements Service {
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private String serviceName;
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private int id;
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public ServiceImpl(String serviceName) {
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// set the service name
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this.serviceName = serviceName;
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// Generate a random id to this service object
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this.id = (int)Math.floor(Math.random()*1000)+1;
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}
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@Override
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public String getName() {
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return serviceName;
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}
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@Override
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public int getId() {
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return id;
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}
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@Override
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public void execute() {
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System.out.println("Service " + getName() + " is now executing with id " + getId());
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}
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}

‎service-locator/src/main/java/com/iluwater/ServiceLocator.java‎

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package com.iluwater;
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/**
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* The service locator module.
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* Will fetch service from cache, otherwise creats a fresh service and update cache
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*
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* @author saifasif
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*
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*/
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public class ServiceLocator {
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private static ServiceCache serviceCache = new ServiceCache();
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/**
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* Fetch the service with the name param from the cache first,
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* if no service is found, lookup the service from the {@link InitContext} and
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* then add the newly created service into the cache map for future requests.
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* @param serviceJndiName
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* @return {@link Service}
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*/
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public static Service getService(String serviceJndiName){
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Service serviceObj = serviceCache.getService(serviceJndiName);
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if ( serviceObj != null ){
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return serviceObj;
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} else {
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/*
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* If we are unable to retrive anything from cache, then
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* lookup the service and add it in the cache map
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*/
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InitContext ctx = new InitContext();
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serviceObj = (Service) ctx.lookup(serviceJndiName);
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serviceCache.addService(serviceObj);
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return serviceObj;
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}
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}
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}

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