#564: Collection Pipeline pattern

collection-pipeline/README.md

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+---
+layout: pattern
+title: Collection Pipeline
+folder: collection-pipeline
+permalink: /patterns/collection-pipeline/
+categories: Functional
+tags:
+ - Java
+ - Difficulty-Beginner
+ - Functional
+---
+
+## Intent
+Collection Pipeline introduces Function Composition and Collection Pipeline, two functional-style patterns that you can combine to iterate collections in your code. 
+In functional programming, it's common to sequence complex operations through a series of smaller modular functions or operations. The series is called a composition of functions, or a function composition. When a collection of data flows through a function composition, it becomes a collection pipeline. Function Composition and Collection Pipeline are two design patterns frequently used in functional-style programming.
+
+![alt text](./etc/collection-pipeline.png "Collection Pipeline")
+
+## Applicability
+Use the Collection Pipeline pattern when
+
+* When you want to perform a sequence of operations where one operation's collected output is fed into the next
+* When you use a lot of statements in your code
+* When you use a lot of loops in your code
+
+## Credits
+
+* [Function composition and the Collection Pipeline pattern](https://www.ibm.com/developerworks/library/j-java8idioms2/index.html)
+* [Martin Fowler](https://martinfowler.com/articles/collection-pipeline/)

collection-pipeline/etc/collection-pipeline.ucls

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+<?xml version="1.0" encoding="UTF-8"?>
+<class-diagram version="1.2.2" icons="true" always-add-relationships="false" generalizations="true" realizations="true" 
+  associations="true" dependencies="false" nesting-relationships="true" router="FAN">  
+  <class id="1" language="java" name="com.iluwatar.collectionpipeline.App" project="collection-pipeline" 
+    file="/collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/App.java" binary="false" 
+    corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="952" y="278"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </class>  
+  <class id="2" language="java" name="com.iluwatar.collectionpipeline.ImperativeProgramming" 
+    project="collection-pipeline" 
+    file="/collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/ImperativeProgramming.java" binary="false" 
+    corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="552" y="107"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </class>  
+  <class id="3" language="java" name="com.iluwatar.collectionpipeline.Car" project="collection-pipeline" 
+    file="/collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/Car.java" binary="false" 
+    corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="476" y="301"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </class>  
+  <class id="4" language="java" name="com.iluwatar.collectionpipeline.FunctionalProgramming" 
+    project="collection-pipeline" 
+    file="/collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/FunctionalProgramming.java" binary="false" 
+    corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="914" y="105"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </class>  
+  <class id="5" language="java" name="com.iluwatar.collectionpipeline.Iterating" project="collection-pipeline" 
+    file="/collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/Iterating.java" binary="false" 
+    corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="723" y="280"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </class>  
+  <classifier-display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+    sort-features="false" accessors="true" visibility="true">    
+    <attributes public="true" package="true" protected="true" private="true" static="true"/>    
+    <operations public="true" package="true" protected="true" private="true" static="true"/>  
+  </classifier-display>  
+  <association-display labels="true" multiplicity="true"/>
+</class-diagram>

collection-pipeline/pom.xml

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+<!--
+
+    The MIT License
+    Copyright (c) 2014 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 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">
+  <modelVersion>4.0.0</modelVersion>
+  <parent>
+    <groupId>com.iluwatar</groupId>
+    <artifactId>java-design-patterns</artifactId>
+    <version>1.20.0-SNAPSHOT</version>
+  </parent>
+  <artifactId>collection-pipeline</artifactId>
+  <dependencies>
+    <dependency>
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter-api</artifactId>
+      <scope>test</scope>
+    </dependency>
+    <dependency>
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter-engine</artifactId>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+</project>

collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/App.java

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+/**
+ * The MIT License
+ * Copyright (c) 2014 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.collectionpipeline;
+
+import java.util.List;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * In imperative-style programming, it is common to use for and while loops for
+ * most kinds of data processing. Function composition is a simple technique
+ * that lets you sequence modular functions to create more complex operations.
+ * When you run data through the sequence, you have a collection pipeline.
+ * Together, the Function Composition and Collection Pipeline patterns enable
+ * you to create sophisticated programs where data flow from upstream to
+ * downstream and is passed through a series of transformations.
+ *
+ */
+public class App {
+
+  private static final Logger LOGGER = LoggerFactory.getLogger(App.class);
+
+  /**
+   * Program entry point.
+   * 
+   * @param args
+   *            command line args
+   */
+  public static void main(String[] args) {
+
+    List<Car> cars = Iterating.createCars();
+    
+    List<String> modelsImperative = ImperativeProgramming.getModelsAfter2000UsingFor(cars);
+    LOGGER.info(modelsImperative.toString());
+
+    List<String> modelsFunctional = FunctionalProgramming.getModelsAfter2000UsingPipeline(cars);
+    LOGGER.info(modelsFunctional.toString());
+  }
+}

collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/Car.java

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+/**
+ * The MIT License
+ * Copyright (c) 2014 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.collectionpipeline;
+
+/**
+ * A Car class that has the properties of make, model, and year.
+ */
+public class Car {
+  private String make;
+  private String model;
+  private int year;
+
+  /**
+   * Constructor to create an instance of car.
+   * @param theMake the make of the car
+   * @param theModel the model of the car
+   * @param yearOfMake the year of built of the car
+   */
+  public Car(String theMake, String theModel, int yearOfMake) {
+    make = theMake;
+    model = theModel;
+    year = yearOfMake;
+  }
+
+  public String getMake() {
+    return make;
+  }
+
+  public String getModel() {
+    return model;
+  }
+
+  public int getYear() {
+    return year;
+  }
+}

collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/FunctionalProgramming.java

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+/**
+ * The MIT License
+ * Copyright (c) 2014 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.collectionpipeline;
+
+import java.util.Comparator;
+import java.util.List;
+import java.util.stream.Collectors;
+
+/**
+ * Iterating and sorting with a collection pipeline
+ * 
+ * <p>In functional programming, it's common to sequence complex operations through
+ * a series of smaller modular functions or operations. The series is called a
+ * composition of functions, or a function composition. When a collection of
+ * data flows through a function composition, it becomes a collection pipeline.
+ * Function Composition and Collection Pipeline are two design patterns
+ * frequently used in functional-style programming.
+ * 
+ * <p>Instead of passing a lambda expression to the map method, we passed the
+ * method reference Car::getModel. Likewise, instead of passing the lambda
+ * expression car -> car.getYear() to the comparing method, we passed the method
+ * reference Car::getYear. Method references are short, concise, and expressive.
+ * It is best to use them wherever possible.
+ * 
+ */
+public class FunctionalProgramming {
+  private FunctionalProgramming() {
+  }
+
+  /**
+   * Method to get models using for collection pipeline.
+   * 
+   * @param cars {@link List} of {@link Car} to be used for filtering
+   * @return {@link List} of {@link String} representing models built after year 2000
+   */
+  public static List<String> getModelsAfter2000UsingPipeline(List<Car> cars) {
+    return cars.stream().filter(car -> car.getYear() > 2000)
+      .sorted(Comparator.comparing(Car::getYear))
+      .map(Car::getModel).collect(Collectors.toList());
+  }
+}

collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/ImperativeProgramming.java

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+/**
+ * The MIT License
+ * Copyright (c) 2014 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.collectionpipeline;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.List;
+
+/**
+ * Imperative-style programming to iterate over the list and get the names of
+ * cars made later than the year 2000. We then sort the models in ascending
+ * order by year.
+ * 
+ * <p>As you can see, there's a lot of looping in this code. First, the
+ * getModelsAfter2000UsingFor method takes a list of cars as its parameter. It
+ * extracts or filters out cars made after the year 2000, putting them into a
+ * new list named carsSortedByYear. Next, it sorts that list in ascending order
+ * by year-of-make. Finally, it loops through the list carsSortedByYear to get
+ * the model names and returns them in a list.
+ * 
+ * <p>This short example demonstrates what I call the effect of statements. While
+ * functions and methods in general can be used as expressions, the {@link Collections}
+ * sort method doesn't return a result. Because it is used as a statement, it
+ * mutates the list given as argument. Both of the for loops also mutate lists
+ * as they iterate. Being statements, that's just how these elements work. As a
+ * result, the code contains unnecessary garbage variables
+ */
+public class ImperativeProgramming {
+  private ImperativeProgramming() {
+  }
+
+  /**
+   * Method to return the car models built after year 2000 using for loops.
+   * @param cars {@link List} of {@link Car} to iterate over
+   * @return {@link List} of {@link String} of car models built after year 2000
+   */
+  public static List<String> getModelsAfter2000UsingFor(List<Car> cars) {
+    List<Car> carsSortedByYear = new ArrayList<>();
+
+    for (Car car : cars) {
+      if (car.getYear() > 2000) {
+        carsSortedByYear.add(car);
+      }
+    }
+
+    Collections.sort(carsSortedByYear, new Comparator<Car>() {
+      public int compare(Car car1, Car car2) {
+        return new Integer(car1.getYear()).compareTo(car2.getYear());
+      }
+    });
+
+    List<String> models = new ArrayList<>();
+    for (Car car : carsSortedByYear) {
+      models.add(car.getModel());
+    }
+
+    return models;
+  }
+}

collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/Iterating.java

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+/**
+ * The MIT License
+ * Copyright (c) 2014 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.collectionpipeline;
+
+import java.util.Arrays;
+import java.util.List;
+
+/**
+ * A factory class to create a collection of {@link Car} instances.
+ */
+public class Iterating {
+  private Iterating() {
+  }
+
+  /**
+   * Factory method to create a {@link List} of {@link Car} instances.
+   * @return {@link List} of {@link Car}
+   */
+  public static List<Car> createCars() {
+    return Arrays.asList(new Car("Jeep", "Wrangler", 2011), new Car("Jeep", "Comanche", 1990),
+        new Car("Dodge", "Avenger", 2010),
+        new Car("Buick", "Cascada", 2016),
+        new Car("Ford", "Focus", 2012),
+        new Car("Chevrolet", "Geo Metro", 1992));
+  }
+}

collection-pipeline/src/test/java/com/iluwatar/collectionpipeline/AppTest.java

@@ -0,0 +1,50 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 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.collectionpipeline;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.Arrays;
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Tests that Collection Pipeline methods work as expected.
+ */
+public class AppTest {
+  
+  private List<Car> cars = Iterating.createCars();
+  
+  @Test
+  public void testGetModelsAfter2000UsingFor() {
+    List<String> models = ImperativeProgramming.getModelsAfter2000UsingFor(cars);
+    assertEquals(models, Arrays.asList("Avenger", "Wrangler", "Focus", "Cascada"));
+  }
+  
+  @Test
+  public void testGetModelsAfter2000UsingPipeline() {
+    List<String> models = FunctionalProgramming.getModelsAfter2000UsingPipeline(cars);
+    assertEquals(models, Arrays.asList("Avenger", "Wrangler", "Focus", "Cascada"));
+  }
+}

pom.xml

@@ -161,6 +161,7 @@
         <module>dirty-flag</module>
         <module>trampoline</module>
         <module>serverless</module>
+	    <module>collection-pipeline</module>
     </modules>
 
     <repositories>