Merge branch 'master' of https://github.com/besok/java-design-patterns

pom.xml

@@ -183,6 +183,8 @@
         <module>data-locality</module>
         <module>subclass-sandbox</module>
         <module>circuit-breaker</module>
+        <module>role-object</module>
+		<module>saga</module>
         <module>double-buffer</module>
         <module>sharding</module>
     </modules>

saga/README.md

@@ -0,0 +1,46 @@
+---
+layout: pattern
+title: Saga
+folder: saga
+permalink: /patterns/saga/
+categories: Behavioral
+tags:
+ - Java
+ - Difficulty-Expert
+ - Idiom
+ - Distributed communication
+---
+
+## Also known as
+This pattern has a similar goal with two-phase commit (XA transaction)
+
+## Intent
+This pattern is used in distributed services to perform a group of operations atomically.
+This is an analog of transaction in a database but in terms of microservices architecture this is executed 
+in a distributed environment
+
+## Explanation
+A saga is a sequence of local transactions in a certain context. If one transaction fails for some reason, 
+the saga executes compensating transactions(rollbacks) to undo the impact of the preceding transactions.
+There are two types of Saga:
+
+- Choreography-Based Saga. 
+In this approach, there is no central orchestrator. 
+Each service participating in the Saga performs their transaction and publish events. 
+The other services act upon those events and perform their transactions. 
+Also, they may or not publish other events based on the situation.
+
+- Orchestration-Based Saga
+In this approach, there is a Saga orchestrator that manages all the transactions and directs 
+the participant services to execute local transactions based on events. 
+This orchestrator can also be though of as a Saga Manager.
+
+## Applicability
+Use the Saga pattern, if:
+- you need to perform a group of operations related to different microservices atomically
+- you need to rollback changes in different places in case of failure one of the operation
+- you need to take care of data consistency in different places including different databases
+- you can not use 2PC(two phase commit)
+
+## Credits
+- [Pattern: Saga](https://microservices.io/patterns/data/saga.html)

saga/pom.xml

@@ -0,0 +1,45 @@
+<?xml version="1.0"?>
+<!--
+
+    The MIT License
+    Copyright © 2014-2019 Ilkka Seppälä
+
+    Permission is hereby granted, free of charge, to any person obtaining a copy
+    of this software and associated documentation files (the "Software"), to deal
+    in the Software without restriction, including without limitation the rights
+    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+    copies of the Software, and to permit persons to whom the Software is
+    furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included in
+    all copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+    THE SOFTWARE.
+
+-->
+<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"
+         xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
+    <modelVersion>4.0.0</modelVersion>
+    <parent>
+        <groupId>com.iluwatar</groupId>
+        <artifactId>java-design-patterns</artifactId>
+        <version>1.22.0-SNAPSHOT</version>
+    </parent>
+
+    <artifactId>saga</artifactId>
+    <dependencies>
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+</project>

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

@@ -0,0 +1,65 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.saga.choreography;
+
+
+/**
+ * ChoreographyChapter is an interface representing a contract for an external service.
+ * In that case, a service needs to make a decision what to do further
+ * hence the server needs to get all context representing {@link Saga}
+ */
+public interface ChoreographyChapter {
+
+  /**
+   * In that case, every method is responsible to make a decision on what to do then.
+   *
+   * @param saga incoming saga
+   * @return saga result
+   */
+  Saga execute(Saga saga);
+
+  /**
+   * get name method.
+   * @return service name.
+   */
+  String getName();
+
+  /**
+   * The operation executed in general case.
+   *
+   * @param saga incoming saga
+   * @return result {@link Saga}
+   */
+  Saga process(Saga saga);
+
+  /**
+   * The operation executed in rollback case.
+   *
+   * @param saga incoming saga
+   * @return result {@link Saga}
+   */
+  Saga rollback(Saga saga);
+
+
+}

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

@@ -0,0 +1,39 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.saga.choreography;
+
+
+/**
+ * Class representing a service to book a fly.
+ */
+public class FlyBookingService extends Service {
+  public FlyBookingService(ServiceDiscoveryService service) {
+    super(service);
+  }
+
+  @Override
+  public String getName() {
+    return "booking a Fly";
+  }
+}

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

@@ -0,0 +1,41 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.saga.choreography;
+
+
+/**
+ * Class representing a service to book a hotel.
+ */
+public class HotelBookingService extends Service {
+  public HotelBookingService(ServiceDiscoveryService service) {
+    super(service);
+  }
+
+  @Override
+  public String getName() {
+    return "booking a Hotel";
+  }
+
+
+}

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

@@ -0,0 +1,40 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.saga.choreography;
+
+
+/**
+ * Class representing a service to init a new order.
+ */
+public class OrderService extends Service {
+
+  public OrderService(ServiceDiscoveryService service) {
+    super(service);
+  }
+
+  @Override
+  public String getName() {
+    return "init an order";
+  }
+}

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

@@ -0,0 +1,217 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.saga.choreography;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+/**
+ * Saga representation.
+ * Saga consists of chapters.
+ * Every ChoreographyChapter is executed a certain service.
+ */
+public class Saga {
+
+  private List<Chapter> chapters;
+  private int pos;
+  private boolean forward;
+  private boolean finished;
+
+
+  public static Saga create() {
+    return new Saga();
+  }
+
+  /**
+   * get resuzlt of saga.
+   *
+   * @return result of saga @see {@link SagaResult}
+   */
+  public SagaResult getResult() {
+    if (finished) {
+      return forward
+          ? SagaResult.FINISHED
+          : SagaResult.ROLLBACKED;
+    }
+
+    return SagaResult.PROGRESS;
+  }
+
+  /**
+   * add chapter to saga.
+   * @param name chapter name
+   * @return this
+   */
+  public Saga chapter(String name) {
+    this.chapters.add(new Chapter(name));
+    return this;
+  }
+
+  /**
+   * set value to last chapter.
+   * @param value invalue
+   * @return this
+   */
+  public Saga setInValue(Object value) {
+    if (chapters.isEmpty()) {
+      return this;
+    }
+    chapters.get(chapters.size() - 1).setInValue(value);
+    return this;
+  }
+
+  /**
+   * get value from current chapter.
+   * @return value
+   */
+  public Object getCurrentValue() {
+    return chapters.get(pos).getInValue();
+  }
+
+  /**
+   * set value to current chapter.
+   * @param value to set
+   */
+  public void setCurrentValue(Object value) {
+    chapters.get(pos).setInValue(value);
+  }
+
+  /**
+   * set status for current chapter.
+   * @param result to set
+   */
+  public void setCurrentStatus(ChapterResult result) {
+    chapters.get(pos).setResult(result);
+  }
+
+  void setFinished(boolean finished) {
+    this.finished = finished;
+  }
+
+  boolean isForward() {
+    return forward;
+  }
+
+  int forward() {
+    return ++pos;
+  }
+
+  int back() {
+    this.forward = false;
+    return --pos;
+  }
+
+
+  private Saga() {
+    this.chapters = new ArrayList<>();
+    this.pos = 0;
+    this.forward = true;
+    this.finished = false;
+  }
+
+  Chapter getCurrent() {
+    return chapters.get(pos);
+  }
+
+
+  boolean isPresent() {
+    return pos >= 0 && pos < chapters.size();
+  }
+
+  boolean isCurrentSuccess() {
+    return chapters.get(pos).isSuccess();
+  }
+
+  /**
+   * Class presents a chapter status and incoming
+   * parameters(incoming parameter transforms to outcoming parameter).
+   */
+  public static class Chapter {
+    private String name;
+    private ChapterResult result;
+    private Object inValue;
+
+
+    public Chapter(String name) {
+      this.name = name;
+      this.result = ChapterResult.INIT;
+    }
+
+    public Object getInValue() {
+      return inValue;
+    }
+
+    public void setInValue(Object object) {
+      this.inValue = object;
+    }
+
+    public String getName() {
+      return name;
+    }
+
+    /**
+     * set result.
+     * @param result {@link ChapterResult}
+     */
+    public void setResult(ChapterResult result) {
+      this.result = result;
+    }
+
+    /**
+     * the result for chapter is good.
+     * @return true if is good otherwise bad
+     */
+    public boolean isSuccess() {
+      return result == ChapterResult.SUCCESS;
+    }
+  }
+
+
+  /**
+   * result for chapter.
+   */
+  public enum ChapterResult {
+    INIT, SUCCESS, ROLLBACK
+  }
+
+  /**
+   * result for saga.
+   */
+  public enum SagaResult {
+    PROGRESS, FINISHED, ROLLBACKED
+  }
+
+  @Override
+  public String toString() {
+    return "Saga{"
+        + "chapters="
+        + Arrays.toString(chapters.toArray())
+        + ", pos="
+        + pos
+        + ", forward="
+        + forward
+        + '}';
+  }
+}

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

@@ -0,0 +1,84 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.saga.choreography;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * This pattern is used in distributed services to perform a group of operations atomically.
+ * This is an analog of transaction in a database but in terms
+ * of microservices architecture this is executed
+ * in a distributed environment
+ *
+ * <p>A saga is a sequence of local transactions in a certain context.
+ * If one transaction fails for some reason,
+ * the saga executes compensating transactions(rollbacks)
+ * to undo the impact of the preceding transactions.
+ *
+ * <p>In this approach, there are no mediators or orchestrators services.
+ * All chapters are handled and moved by services manually.
+ *
+ * <p>The major difference with choreography saga is an ability to handle crashed services
+ * (otherwise in choreography services very hard to prevent a saga
+ * if one of them has been crashed)
+ *
+ * @see com.iluwatar.saga.choreography.Saga
+ * @see Service
+ */
+public class SagaApplication {
+  private static final Logger LOGGER = LoggerFactory.getLogger(SagaApplication.class);
+
+  /**
+   * main method.
+   */
+  public static void main(String[] args) {
+    ServiceDiscoveryService sd = serviceDiscovery();
+    ChoreographyChapter service = sd.findAny();
+    Saga goodOrderSaga = service.execute(newSaga("good_order"));
+    Saga badOrderSaga = service.execute(newSaga("bad_order"));
+    LOGGER.info("orders: goodOrder is {}, badOrder is {}",
+        goodOrderSaga.getResult(), badOrderSaga.getResult());
+
+  }
+
+
+  private static Saga newSaga(Object value) {
+    return Saga
+        .create()
+        .chapter("init an order").setInValue(value)
+        .chapter("booking a Fly")
+        .chapter("booking a Hotel")
+        .chapter("withdrawing Money");
+  }
+
+  private static ServiceDiscoveryService serviceDiscovery() {
+    ServiceDiscoveryService sd = new ServiceDiscoveryService();
+    return sd
+        .discover(new OrderService(sd))
+        .discover(new FlyBookingService(sd))
+        .discover(new HotelBookingService(sd))
+        .discover(new WithdrawMoneyService(sd));
+  }
+}

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

@@ -0,0 +1,113 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.saga.choreography;
+
+import java.util.function.Supplier;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+
+/**
+ * Common abstraction class representing services.
+ * implementing a general contract @see {@link ChoreographyChapter}
+ */
+public abstract class Service implements ChoreographyChapter {
+  protected static final Logger LOGGER = LoggerFactory.getLogger(Service.class);
+
+  private final ServiceDiscoveryService sd;
+
+  public Service(ServiceDiscoveryService service) {
+    this.sd = service;
+  }
+
+  @Override
+  public Saga execute(Saga saga) {
+    Saga nextSaga = saga;
+    Object nextVal;
+    String chapterName = saga.getCurrent().getName();
+    if (chapterName.equals(getName())) {
+      if (saga.isForward()) {
+        nextSaga = process(saga);
+        nextVal = nextSaga.getCurrentValue();
+        if (nextSaga.isCurrentSuccess()) {
+          nextSaga.forward();
+        } else {
+          nextSaga.back();
+        }
+      } else {
+        nextSaga = rollback(saga);
+        nextVal = nextSaga.getCurrentValue();
+        nextSaga.back();
+      }
+
+      if (isSagaFinished(nextSaga)) {
+        return nextSaga;
+      }
+
+      nextSaga.setCurrentValue(nextVal);
+    }
+    Saga finalNextSaga = nextSaga;
+
+    return sd.find(chapterName).map(ch -> ch.execute(finalNextSaga))
+        .orElseThrow(serviceNotFoundException(chapterName));
+  }
+
+  private Supplier<RuntimeException> serviceNotFoundException(String chServiceName) {
+    return () -> new RuntimeException(
+        String.format("the service %s has not been found", chServiceName));
+  }
+
+  @Override
+  public Saga process(Saga saga) {
+    Object inValue = saga.getCurrentValue();
+    LOGGER.info("The chapter '{}' has been started. "
+            + "The data {} has been stored or calculated successfully",
+        getName(), inValue);
+    saga.setCurrentStatus(Saga.ChapterResult.SUCCESS);
+    saga.setCurrentValue(inValue);
+    return saga;
+  }
+
+  @Override
+  public Saga rollback(Saga saga) {
+    Object inValue = saga.getCurrentValue();
+    LOGGER.info("The Rollback for a chapter '{}' has been started. "
+            + "The data {} has been rollbacked successfully",
+        getName(), inValue);
+
+    saga.setCurrentStatus(Saga.ChapterResult.ROLLBACK);
+    saga.setCurrentValue(inValue);
+    return saga;
+  }
+
+  private boolean isSagaFinished(Saga saga) {
+    if (!saga.isPresent()) {
+      saga.setFinished(true);
+      LOGGER.info(" the saga has been finished with {} status", saga.getResult());
+      return true;
+    }
+    return false;
+  }
+
+}

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

@@ -0,0 +1,61 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.saga.choreography;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.NoSuchElementException;
+import java.util.Optional;
+
+/**
+ * The class representing a service discovery pattern.
+ */
+public class ServiceDiscoveryService {
+  private Map<String, ChoreographyChapter> services;
+
+  /**
+   * find any service.
+   *
+   * @return any service
+   * @throws NoSuchElementException if no elements further
+   */
+  public ChoreographyChapter findAny() {
+    return services.values().iterator().next();
+  }
+
+  public Optional<ChoreographyChapter> find(String service) {
+    return Optional.ofNullable(services.getOrDefault(service, null));
+  }
+
+  public ServiceDiscoveryService discover(ChoreographyChapter chapterService) {
+    services.put(chapterService.getName(), chapterService);
+    return this;
+  }
+
+  public ServiceDiscoveryService() {
+    this.services = new HashMap<>();
+  }
+
+
+}

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

@@ -0,0 +1,53 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.saga.choreography;
+
+/**
+ * Class representing a service to withdraw a money.
+ */
+public class WithdrawMoneyService extends Service {
+
+  public WithdrawMoneyService(ServiceDiscoveryService service) {
+    super(service);
+  }
+
+  @Override
+  public String getName() {
+    return "withdrawing Money";
+  }
+
+  @Override
+  public Saga process(Saga saga) {
+    Object inValue = saga.getCurrentValue();
+
+    if (inValue.equals("bad_order")) {
+      LOGGER.info("The chapter '{}' has been started. But the exception has been raised."
+              + "The rollback is about to start",
+          getName(), inValue);
+      saga.setCurrentStatus(Saga.ChapterResult.ROLLBACK);
+      return saga;
+    }
+    return super.process(saga);
+  }
+}

saga/src/main/java/com/iluwatar/saga/orchestration/ChapterResult.java

@@ -0,0 +1,62 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.saga.orchestration;
+
+/**
+ * Executing result for chapter.
+ *
+ * @param <K> incoming value
+ */
+public class ChapterResult<K> {
+  private K value;
+  private State state;
+
+  public K getValue() {
+    return value;
+  }
+
+  ChapterResult(K value, State state) {
+    this.value = value;
+    this.state = state;
+  }
+
+  public boolean isSuccess() {
+    return state == State.SUCCESS;
+  }
+
+  public static <K> ChapterResult<K> success(K val) {
+    return new ChapterResult<>(val, State.SUCCESS);
+  }
+
+  public static <K> ChapterResult<K> failure(K val) {
+    return new ChapterResult<>(val, State.FAILURE);
+  }
+
+  /**
+   * state for chapter.
+   */
+  public enum State {
+    SUCCESS, FAILURE
+  }
+}

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

@@ -0,0 +1,34 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.saga.orchestration;
+
+/**
+ * Class representing a service to book a fly.
+ */
+public class FlyBookingService extends Service<String> {
+  @Override
+  public String getName() {
+    return "booking a Fly";
+  }
+}

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

@@ -0,0 +1,52 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.saga.orchestration;
+
+/**
+ * Class representing a service to book a hotel.
+ */
+public class HotelBookingService extends Service<String> {
+  @Override
+  public String getName() {
+    return "booking a Hotel";
+  }
+
+
+  @Override
+  public ChapterResult<String> rollback(String value) {
+    if (value.equals("crashed_order")) {
+      LOGGER.info("The Rollback for a chapter '{}' has been started. "
+              + "The data {} has been failed.The saga has been crashed.",
+          getName(), value);
+
+      return ChapterResult.failure(value);
+    }
+
+    LOGGER.info("The Rollback for a chapter '{}' has been started. "
+            + "The data {} has been rollbacked successfully",
+        getName(), value);
+
+    return super.rollback(value);
+  }
+}

saga/src/main/java/com/iluwatar/saga/orchestration/OrchestrationChapter.java

@@ -0,0 +1,55 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.saga.orchestration;
+
+/**
+ * ChoreographyChapter is an interface representing a contract for an external service.
+ *
+ * @param <K> is type for passing params
+ */
+public interface OrchestrationChapter<K> {
+
+  /**
+   * method get name.
+   * @return service name.
+   */
+  String getName();
+
+  /**
+   * The operation executed in general case.
+   *
+   * @param value incoming value
+   * @return result {@link ChapterResult}
+   */
+  ChapterResult<K> process(K value);
+
+  /**
+   * The operation executed in rollback case.
+   *
+   * @param value incoming value
+   * @return result {@link ChapterResult}
+   */
+  ChapterResult<K> rollback(K value);
+
+}

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

@@ -0,0 +1,34 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.saga.orchestration;
+
+/**
+ * Class representing a service to init a new order.
+ */
+public class OrderService extends Service<String> {
+  @Override
+  public String getName() {
+    return "init an order";
+  }
+}

saga/src/main/java/com/iluwatar/saga/orchestration/Saga.java

@@ -0,0 +1,84 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.saga.orchestration;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Saga representation.
+ * Saga consists of chapters.
+ * Every ChoreographyChapter is executed by a certain service.
+ */
+public class Saga {
+
+  private List<Chapter> chapters;
+
+
+  private Saga() {
+    this.chapters = new ArrayList<>();
+  }
+
+
+  public Saga chapter(String name) {
+    this.chapters.add(new Chapter(name));
+    return this;
+  }
+
+
+  public Chapter get(int idx) {
+    return chapters.get(idx);
+  }
+
+  public boolean isPresent(int idx) {
+    return idx >= 0 && idx < chapters.size();
+  }
+
+
+  public static Saga create() {
+    return new Saga();
+  }
+
+  /**
+   * result for saga.
+   */
+  public enum Result {
+    FINISHED, ROLLBACK, CRASHED
+  }
+
+  /**
+   * class represents chapter name.
+   */
+  public static class Chapter {
+    String name;
+
+    public Chapter(String name) {
+      this.name = name;
+    }
+
+    public String getName() {
+      return name;
+    }
+  }
+}

saga/src/main/java/com/iluwatar/saga/orchestration/SagaApplication.java

@@ -0,0 +1,87 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.saga.orchestration;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * This pattern is used in distributed services to perform
+ * a group of operations atomically.
+ * This is an analog of transaction in a database but in terms
+ * of microservices architecture this is executed
+ * in a distributed environment
+ *
+ * <p>A saga is a sequence of local transactions in a certain context.
+ * If one transaction fails for some reason,
+ * the saga executes compensating transactions(rollbacks)
+ * to undo the impact of the preceding transactions.
+ *
+ * <p>In this approach, there is an orchestrator @see {@link SagaOrchestrator}
+ * that manages all the transactions and directs
+ * the participant services to execute local transactions based on events.
+ * The major difference with choreography saga is an ability to handle crashed services
+ * (otherwise in choreography services very hard to prevent a saga
+ * if one of them has been crashed)
+ *
+ * @see Saga
+ * @see SagaOrchestrator
+ * @see Service
+ */
+public class SagaApplication {
+  private static final Logger LOGGER = LoggerFactory.getLogger(SagaApplication.class);
+
+  /**
+   * method to show common saga logic.
+   */
+  public static void main(String[] args) {
+    SagaOrchestrator sagaOrchestrator = new SagaOrchestrator(newSaga(), serviceDiscovery());
+
+    Saga.Result goodOrder = sagaOrchestrator.execute("good_order");
+    Saga.Result badOrder = sagaOrchestrator.execute("bad_order");
+    Saga.Result crashedOrder = sagaOrchestrator.execute("crashed_order");
+
+    LOGGER.info("orders: goodOrder is {}, badOrder is {},crashedOrder is {}",
+        goodOrder, badOrder, crashedOrder);
+  }
+
+
+  private static Saga newSaga() {
+    return Saga
+        .create()
+        .chapter("init an order")
+        .chapter("booking a Fly")
+        .chapter("booking a Hotel")
+        .chapter("withdrawing Money");
+  }
+
+  private static ServiceDiscoveryService serviceDiscovery() {
+    return
+        new ServiceDiscoveryService()
+            .discover(new OrderService())
+            .discover(new FlyBookingService())
+            .discover(new HotelBookingService())
+            .discover(new WithdrawMoneyService());
+  }
+}

saga/src/main/java/com/iluwatar/saga/orchestration/SagaOrchestrator.java

@@ -0,0 +1,148 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.saga.orchestration;
+
+import static com.iluwatar.saga.orchestration.Saga.Result.CRASHED;
+import static com.iluwatar.saga.orchestration.Saga.Result.FINISHED;
+import static com.iluwatar.saga.orchestration.Saga.Result.ROLLBACK;
+
+import java.util.Optional;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+
+/**
+ * The orchestrator that manages all the transactions and directs
+ * the participant services to execute local transactions based on events.
+ */
+public class SagaOrchestrator {
+  private static final Logger LOGGER = LoggerFactory.getLogger(SagaOrchestrator.class);
+  private final Saga saga;
+  private final ServiceDiscoveryService sd;
+  private final CurrentState state;
+
+
+  /**
+   * Create a new service to orchetrate sagas.
+   * @param saga saga to process
+   * @param sd service discovery @see {@link ServiceDiscoveryService}
+   */
+  public SagaOrchestrator(Saga saga, ServiceDiscoveryService sd) {
+    this.saga = saga;
+    this.sd = sd;
+    this.state = new CurrentState();
+  }
+
+  /**
+   * pipeline to execute saga process/story.
+   *
+   * @param value incoming value
+   * @param <K>   type for incoming value
+   * @return result @see {@link Saga.Result}
+   */
+  @SuppressWarnings("unchecked")
+  public <K> Saga.Result execute(K value) {
+    state.cleanUp();
+    LOGGER.info(" The new saga is about to start");
+    Saga.Result result = FINISHED;
+    K tempVal = value;
+
+    while (true) {
+      int next = state.current();
+      Saga.Chapter ch = saga.get(next);
+      Optional<OrchestrationChapter> srvOpt = sd.find(ch.name);
+
+      if (!srvOpt.isPresent()) {
+        state.directionToBack();
+        state.back();
+        continue;
+      }
+
+      OrchestrationChapter srv = srvOpt.get();
+
+      if (state.isForward()) {
+        ChapterResult processRes = srv.process(tempVal);
+        if (processRes.isSuccess()) {
+          next = state.forward();
+          tempVal = (K) processRes.getValue();
+        } else {
+          state.directionToBack();
+        }
+      } else {
+        ChapterResult rlRes = srv.rollback(tempVal);
+        if (rlRes.isSuccess()) {
+          next = state.back();
+          tempVal = (K) rlRes.getValue();
+        } else {
+          result = CRASHED;
+          next = state.back();
+        }
+      }
+
+
+      if (!saga.isPresent(next)) {
+        return state.isForward() ? FINISHED : result == CRASHED ? CRASHED : ROLLBACK;
+      }
+    }
+
+  }
+
+
+  private static class CurrentState {
+    int currentNumber;
+    boolean isForward;
+
+    void cleanUp() {
+      currentNumber = 0;
+      isForward = true;
+    }
+
+    CurrentState() {
+      this.currentNumber = 0;
+      this.isForward = true;
+    }
+
+
+    boolean isForward() {
+      return isForward;
+    }
+
+    void directionToBack() {
+      isForward = false;
+    }
+
+    int forward() {
+      return ++currentNumber;
+    }
+
+    int back() {
+      return --currentNumber;
+    }
+
+    int current() {
+      return currentNumber;
+    }
+  }
+
+}

saga/src/main/java/com/iluwatar/saga/orchestration/Service.java

@@ -0,0 +1,59 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.saga.orchestration;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Common abstraction class representing services.
+ * implementing a general contract @see {@link OrchestrationChapter}
+ *
+ * @param <K> type of incoming param
+ */
+public abstract class Service<K> implements OrchestrationChapter<K> {
+  protected static final Logger LOGGER = LoggerFactory.getLogger(Service.class);
+
+  @Override
+  public abstract String getName();
+
+
+  @Override
+  public ChapterResult<K> process(K value) {
+    LOGGER.info("The chapter '{}' has been started. "
+            + "The data {} has been stored or calculated successfully",
+        getName(), value);
+    return ChapterResult.success(value);
+  }
+
+  @Override
+  public ChapterResult<K> rollback(K value) {
+    LOGGER.info("The Rollback for a chapter '{}' has been started. "
+            + "The data {} has been rollbacked successfully",
+        getName(), value);
+    return ChapterResult.success(value);
+  }
+
+
+}

saga/src/main/java/com/iluwatar/saga/orchestration/ServiceDiscoveryService.java

@@ -0,0 +1,50 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.saga.orchestration;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Optional;
+
+/**
+ * The class representing a service discovery pattern.
+ */
+public class ServiceDiscoveryService {
+  private Map<String, OrchestrationChapter<?>> services;
+
+  public Optional<OrchestrationChapter> find(String service) {
+    return Optional.ofNullable(services.getOrDefault(service, null));
+  }
+
+  public ServiceDiscoveryService discover(OrchestrationChapter<?> orchestrationChapterService) {
+    services.put(orchestrationChapterService.getName(), orchestrationChapterService);
+    return this;
+  }
+
+  public ServiceDiscoveryService() {
+    this.services = new HashMap<>();
+  }
+
+
+}

saga/src/main/java/com/iluwatar/saga/orchestration/WithdrawMoneyService.java

@@ -0,0 +1,45 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.saga.orchestration;
+
+/**
+ * Class representing a service to withdraw a money.
+ */
+public class WithdrawMoneyService extends Service<String> {
+  @Override
+  public String getName() {
+    return "withdrawing Money";
+  }
+
+  @Override
+  public ChapterResult<String> process(String value) {
+    if (value.equals("bad_order") || value.equals("crashed_order")) {
+      LOGGER.info("The chapter '{}' has been started. But the exception has been raised."
+              + "The rollback is about to start",
+          getName(), value);
+      return ChapterResult.failure(value);
+    }
+    return super.process(value);
+  }
+}

saga/src/test/java/com/iluwatar/saga/choreography/SagaApplicationTest.java

@@ -0,0 +1,37 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package com.iluwatar.saga.choreography;
+
+import com.iluwatar.saga.orchestration.SagaApplication;
+import org.junit.Test;
+
+
+/***
+ * empty test
+ */
+public class SagaApplicationTest {
+  @Test
+  public void mainTest() {
+    SagaApplication.main(new String[]{});
+  }
+}

saga/src/test/java/com/iluwatar/saga/choreography/SagaChoreographyTest.java

@@ -0,0 +1,62 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package com.iluwatar.saga.choreography;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+/**
+ * test to check choreography saga
+ */
+public class SagaChoreographyTest {
+
+
+  @Test
+  public void executeTest() {
+    ServiceDiscoveryService sd = serviceDiscovery();
+    ChoreographyChapter service = sd.findAny();
+    Saga badOrderSaga = service.execute(newSaga("bad_order"));
+    Saga goodOrderSaga = service.execute(newSaga("good_order"));
+
+    Assert.assertEquals(badOrderSaga.getResult(), Saga.SagaResult.ROLLBACKED);
+    Assert.assertEquals(goodOrderSaga.getResult(), Saga.SagaResult.FINISHED);
+  }
+
+  private static Saga newSaga(Object value) {
+    return Saga
+        .create()
+        .chapter("init an order").setInValue(value)
+        .chapter("booking a Fly")
+        .chapter("booking a Hotel")
+        .chapter("withdrawing Money");
+  }
+
+  private static ServiceDiscoveryService serviceDiscovery() {
+    ServiceDiscoveryService sd = new ServiceDiscoveryService();
+    return sd
+        .discover(new OrderService(sd))
+        .discover(new FlyBookingService(sd))
+        .discover(new HotelBookingService(sd))
+        .discover(new WithdrawMoneyService(sd));
+  }
+}

saga/src/test/java/com/iluwatar/saga/orchestration/SagaApplicationTest.java

@@ -0,0 +1,38 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package com.iluwatar.saga.orchestration;
+
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+/**
+ * empty test
+ */
+public class SagaApplicationTest {
+
+  @Test
+  public void mainTest() {
+    SagaApplication.main(new String[]{});
+  }
+}

saga/src/test/java/com/iluwatar/saga/orchestration/SagaOrchestratorInternallyTest.java

@@ -0,0 +1,145 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package com.iluwatar.saga.orchestration;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * test to test orchestration logic
+ */
+public class SagaOrchestratorInternallyTest {
+
+  private List<String> records = new ArrayList<>();
+
+  @Test
+  public void executeTest() {
+    SagaOrchestrator sagaOrchestrator = new SagaOrchestrator(newSaga(), serviceDiscovery());
+    Saga.Result result = sagaOrchestrator.execute(1);
+    Assert.assertEquals(result, Saga.Result.ROLLBACK);
+    Assert.assertArrayEquals(
+        records.toArray(new String[]{}),
+        new String[]{"+1", "+2", "+3", "+4", "-4", "-3", "-2", "-1"});
+  }
+
+  private static Saga newSaga() {
+    return Saga
+        .create()
+        .chapter("1")
+        .chapter("2")
+        .chapter("3")
+        .chapter("4");
+  }
+
+  private ServiceDiscoveryService serviceDiscovery() {
+    return
+        new ServiceDiscoveryService()
+            .discover(new Service1())
+            .discover(new Service2())
+            .discover(new Service3())
+            .discover(new Service4());
+  }
+
+  class Service1 extends Service<Integer> {
+
+    @Override
+    public String getName() {
+      return "1";
+    }
+
+    @Override
+    public ChapterResult<Integer> process(Integer value) {
+      records.add("+1");
+      return ChapterResult.success(value);
+    }
+
+    @Override
+    public ChapterResult<Integer> rollback(Integer value) {
+      records.add("-1");
+      return ChapterResult.success(value);
+    }
+  }
+
+  class Service2 extends Service<Integer> {
+
+    @Override
+    public String getName() {
+      return "2";
+    }
+
+    @Override
+    public ChapterResult<Integer> process(Integer value) {
+      records.add("+2");
+      return ChapterResult.success(value);
+    }
+
+    @Override
+    public ChapterResult<Integer> rollback(Integer value) {
+      records.add("-2");
+      return ChapterResult.success(value);
+    }
+  }
+
+  class Service3 extends Service<Integer> {
+
+    @Override
+    public String getName() {
+      return "3";
+    }
+
+    @Override
+    public ChapterResult<Integer> process(Integer value) {
+      records.add("+3");
+      return ChapterResult.success(value);
+    }
+
+    @Override
+    public ChapterResult<Integer> rollback(Integer value) {
+      records.add("-3");
+      return ChapterResult.success(value);
+    }
+  }
+
+  class Service4 extends Service<Integer> {
+
+    @Override
+    public String getName() {
+      return "4";
+    }
+
+    @Override
+    public ChapterResult<Integer> process(Integer value) {
+      records.add("+4");
+      return ChapterResult.failure(value);
+    }
+
+    @Override
+    public ChapterResult<Integer> rollback(Integer value) {
+      records.add("-4");
+      return ChapterResult.success(value);
+    }
+  }
+}

saga/src/test/java/com/iluwatar/saga/orchestration/SagaOrchestratorTest.java

@@ -0,0 +1,60 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package com.iluwatar.saga.orchestration;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+/**
+ * test to check general logic
+ */
+public class SagaOrchestratorTest {
+
+  @Test
+  public void execute() {
+    SagaOrchestrator sagaOrchestrator = new SagaOrchestrator(newSaga(), serviceDiscovery());
+    Saga.Result badOrder = sagaOrchestrator.execute("bad_order");
+    Saga.Result crashedOrder = sagaOrchestrator.execute("crashed_order");
+
+    Assert.assertEquals(badOrder, Saga.Result.ROLLBACK);
+    Assert.assertEquals(crashedOrder, Saga.Result.CRASHED);
+  }
+
+  private static Saga newSaga() {
+    return Saga
+        .create()
+        .chapter("init an order")
+        .chapter("booking a Fly")
+        .chapter("booking a Hotel")
+        .chapter("withdrawing Money");
+  }
+
+  private static ServiceDiscoveryService serviceDiscovery() {
+    return
+        new ServiceDiscoveryService()
+            .discover(new OrderService())
+            .discover(new FlyBookingService())
+            .discover(new HotelBookingService())
+            .discover(new WithdrawMoneyService());
+  }
+}