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Saga pattern (iluwatar#1062)
* init repo for role object * add to init * add to init * add first impl * add pattern * add license * add changes * add saga init dsc * add init saga dsc * add changes to dsc * add * add orchestrator * add ch * separate pkgs * add info * add choreogr * rem space * change according to cgeckstyle * add changes according to google style
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‎pom.xml

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<module>data-locality</module>
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<module>subclass-sandbox</module>
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<module>circuit-breaker</module>
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<module>role-object</module>
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<module>saga</module>
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<module>double-buffer</module>
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<module>sharding</module>
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</modules>

‎role-object/src/main/java/com/iluwatar/roleobject/InvestorRole.java

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}
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public String invest() {
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return String.format("Investor %s has invested %d dollars", name, amountToInvest);
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return String.format("Investor %s has invested %d dollars", name, amountToInvest);
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}
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}

‎saga/README.md

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---
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layout: pattern
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title: Saga
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folder: saga
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permalink: /patterns/saga/
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categories: Behavioral
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tags:
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- Java
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- Difficulty-Expert
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- Idiom
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- Distributed communication
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---
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## Also known as
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This pattern has a similar goal with two-phase commit (XA transaction)
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## Intent
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This pattern is used in distributed services to perform a group of operations atomically.
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This is an analog of transaction in a database but in terms of microservices architecture this is executed
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in a distributed environment
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## Explanation
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A saga is a sequence of local transactions in a certain context. If one transaction fails for some reason,
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the saga executes compensating transactions(rollbacks) to undo the impact of the preceding transactions.
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There are two types of Saga:
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- Choreography-Based Saga.
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In this approach, there is no central orchestrator.
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Each service participating in the Saga performs their transaction and publish events.
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The other services act upon those events and perform their transactions.
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Also, they may or not publish other events based on the situation.
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- Orchestration-Based Saga
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In this approach, there is a Saga orchestrator that manages all the transactions and directs
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the participant services to execute local transactions based on events.
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This orchestrator can also be though of as a Saga Manager.
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## Applicability
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Use the Saga pattern, if:
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- you need to perform a group of operations related to different microservices atomically
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- you need to rollback changes in different places in case of failure one of the operation
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- you need to take care of data consistency in different places including different databases
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- you can not use 2PC(two phase commit)
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## Credits
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- [Pattern: Saga](https://microservices.io/patterns/data/saga.html)

‎saga/pom.xml

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<?xml version="1.0"?>
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<!--
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The MIT License
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Copyright © 2014-2019 Ilkka Seppälä
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Permission is hereby granted, free of charge, to any person obtaining a copy
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of this software and associated documentation files (the "Software"), to deal
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in the Software without restriction, including without limitation the rights
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to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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copies of the Software, and to permit persons to whom the Software is
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furnished to do so, subject to the following conditions:
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The above copyright notice and this permission notice shall be included in
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all copies or substantial portions of the Software.
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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THE SOFTWARE.
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-->
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<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"
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xmlns="http://maven.apache.org/POM/4.0.0"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
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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>1.22.0-SNAPSHOT</version>
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</parent>
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<artifactId>saga</artifactId>
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<dependencies>
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<dependency>
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<groupId>junit</groupId>
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<artifactId>junit</artifactId>
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<scope>test</scope>
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</dependency>
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</dependencies>
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</project>

‎saga/src/main/java/com/iluwatar/saga/choreography/ChoreographyChapter.java

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/*
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* The MIT License
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* Copyright © 2014-2019 Ilkka Seppälä
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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package com.iluwatar.saga.choreography;
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/**
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* ChoreographyChapter is an interface representing a contract for an external service.
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* In that case, a service needs to make a decision what to do further
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* hence the server needs to get all context representing {@link Saga}
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*/
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public interface ChoreographyChapter {
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/**
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* In that case, every method is responsible to make a decision on what to do then.
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*
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* @param saga incoming saga
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* @return saga result
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*/
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Saga execute(Saga saga);
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/**
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* get name method.
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* @return service name.
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*/
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String getName();
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/**
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* The operation executed in general case.
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*
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* @param saga incoming saga
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* @return result {@link Saga}
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*/
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Saga process(Saga saga);
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/**
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* The operation executed in rollback case.
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*
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* @param saga incoming saga
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* @return result {@link Saga}
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*/
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Saga rollback(Saga saga);
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}

‎saga/src/main/java/com/iluwatar/saga/choreography/FlyBookingService.java

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/*
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* The MIT License
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* Copyright © 2014-2019 Ilkka Seppälä
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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package com.iluwatar.saga.choreography;
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/**
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* Class representing a service to book a fly.
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*/
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public class FlyBookingService extends Service {
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public FlyBookingService(ServiceDiscoveryService service) {
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super(service);
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}
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@Override
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public String getName() {
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return "booking a Fly";
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}
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}

‎saga/src/main/java/com/iluwatar/saga/choreography/HotelBookingService.java

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/*
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* The MIT License
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* Copyright © 2014-2019 Ilkka Seppälä
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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package com.iluwatar.saga.choreography;
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/**
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* Class representing a service to book a hotel.
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*/
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public class HotelBookingService extends Service {
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public HotelBookingService(ServiceDiscoveryService service) {
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super(service);
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}
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@Override
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public String getName() {
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return "booking a Hotel";
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}
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}

‎saga/src/main/java/com/iluwatar/saga/choreography/OrderService.java

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/*
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* The MIT License
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* Copyright © 2014-2019 Ilkka Seppälä
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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package com.iluwatar.saga.choreography;
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/**
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* Class representing a service to init a new order.
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*/
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public class OrderService extends Service {
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public OrderService(ServiceDiscoveryService service) {
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super(service);
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}
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@Override
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public String getName() {
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return "init an order";
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}
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}

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