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#496 Pipeline pattern (#967)

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* #496 Add pipeline module to parent pom ✨

* #496: Add main application class and test for pipeline

* #496: Checkstyle format and add log messages on pipeline stages 🎨

* #496: Fill readme sections of pipeline ✨

* #496: Javadocs and checkstyle formatting 🎨

* #496: Follow PMD checks and add more explanation as block comment on App.java

* #496: Apply requested PR changes by iluwatar 🎨
This commit is contained in:
Joshua Jimenez 2019-10-08 14:19:28 +08:00 committed by Ilkka Seppälä
parent 84c4b034a9
commit f903d7e9a9
11 changed files with 464 additions and 0 deletions
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pipeline/README.md Normal file
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---
layout: pattern
title: Pipeline
folder: pipeline
permalink: /patterns/pipeline/
categories: Behavioral
tags:
- Java
- Functional
- Difficulty-Intermediate
---
## Intent
Allows processing of data in a series of stages by giving in an initial input and passing the processed output to be used by the next stages.
## Applicability
Use the Pipeline pattern when you want to
* execute individual stages that yields a final value
* add readability to complex sequence of operations by providing a fluent builder as an interface
* improve testability of code since stages will most likely be doing a single thing, complying to the [Single Responsibility Principle (SRP)](https://java-design-patterns.com/principles/#single-responsibility-principle)
## Typical Use Case
* implement stages and execute them in an ordered manner
## Real world examples
* [java.util.Stream](https://docs.oracle.com/javase/8/docs/api/java/util/stream/package-summary.html)
* [Maven Build Lifecycle](http://maven.apache.org/guides/introduction/introduction-to-the-lifecycle.html)
* [Functional Java](https://github.com/functionaljava/functionaljava)
## Credits
* [The Pipeline Pattern — for fun and profit](https://medium.com/@aaronweatherall/the-pipeline-pattern-for-fun-and-profit-9b5f43a98130)
* [The Pipeline design pattern (in Java)](https://medium.com/@deepakbapat/the-pipeline-design-pattern-in-java-831d9ce2fe21)
* [Pipelines | Microsoft Docs](https://docs.microsoft.com/en-us/previous-versions/msp-n-p/ff963548(v=pandp.10))

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<?xml version="1.0"?>
<!--
The MIT License
Copyright (c) 2014-2016 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>pipeline</artifactId>
<dependencies>
<dependency>
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter-engine</artifactId>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.mockito</groupId>
<artifactId>mockito-core</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
</project>

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pipeline/src/main/java/com.iluwatar.pipeline/App.java Normal file
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/**
* The MIT License
* Copyright (c) 2014-2016 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.pipeline;
/**
* The Pipeline pattern uses ordered stages to process a sequence of input values.
* Each implemented task is represented by a stage of the pipeline. You can think of
* pipelines as similar to assembly lines in a factory, where each item in the assembly
* line is constructed in stages. The partially assembled item is passed from one assembly
* stage to another. The outputs of the assembly line occur in the same order as that of the
* inputs.
*
* Classes used in this example are suffixed with "Handlers", and synonymously refers to the
* "stage".
*/
public class App {
/**
* Specify the initial input type for the first stage handler and the expected output type
* of the last stage handler as type parameters for Pipeline. Use the fluent builder by
* calling addHandler to add more stage handlers on the pipeline.
*/
public static void main(String[] args) {
/*
Suppose we wanted to pass through a String to a series of filtering stages and convert it
as a char array on the last stage.
- Stage handler 1 (pipe): Removing the alphabets, accepts a String input and returns the
processed String output. This will be used by the next handler as its input.
- Stage handler 2 (pipe): Removing the digits, accepts a String input and returns the
processed String output. This shall also be used by the last handler we have.
- Stage handler 3 (pipe): Converting the String input to a char array handler. We would
be returning a different type in here since that is what's specified by the requirement.
This means that at any stages along the pipeline, the handler can return any type of data
as long as it fulfills the requirements for the next handler's input.
Suppose we wanted to add another handler after ConvertToCharArrayHandler. That handler
then is expected to receive an input of char[] array since that is the type being returned
by the previous handler, ConvertToCharArrayHandler.
*/
new Pipeline<>(new RemoveAlphabetsHandler())
.addHandler(new RemoveDigitsHandler())
.addHandler(new ConvertToCharArrayHandler());
}
}

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pipeline/src/main/java/com.iluwatar.pipeline/ConvertToCharArrayHandler.java Normal file
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/**
* The MIT License
* Copyright (c) 2014-2016 Ilkka Seppälä
* <p>
* 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:
* <p>
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
* <p>
* 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.pipeline;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.util.Arrays;
/**
* Stage handler that converts an input String to its char[] array counterpart.
*/
class ConvertToCharArrayHandler implements Handler<String, char[]> {
private final Logger logger = LoggerFactory.getLogger(ConvertToCharArrayHandler.class);
@Override
public char[] process(String input) {
char[] characters = input.toCharArray();
logger.info(String.format("Current handler: %s, input is %s of type %s, output is %s, of type %s",
ConvertToCharArrayHandler.class, input, String.class, Arrays.toString(characters), Character[].class));
return characters;
}
}

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pipeline/src/main/java/com.iluwatar.pipeline/Handler.java Normal file
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/**
* The MIT License
* Copyright (c) 2014-2016 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.pipeline;
/**
* Forms a contract to all stage handlers to accept a certain type of input and return a processed output.
* @param <I> the input type of the handler
* @param <O> the processed output type of the handler
*/
interface Handler<I, O> {
O process(I input);
}

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pipeline/src/main/java/com.iluwatar.pipeline/Pipeline.java Normal file
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/**
* The MIT License
* Copyright (c) 2014-2016 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.pipeline;
/**
* Main Pipeline class that initially sets the current handler. Processed output
* of the initial handler is then passed as the input to the next stage handlers.
* @param <I> the type of the input for the first stage handler
* @param <O> the final stage handler's output type
*/
class Pipeline<I, O> {
private final Handler<I, O> currentHandler;
Pipeline(Handler<I, O> currentHandler) {
this.currentHandler = currentHandler;
}
<K> Pipeline<I, K> addHandler(Handler<O, K> newHandler) {
return new Pipeline<>(input -> newHandler.process(currentHandler.process(input)));
}
O execute(I input) {
return currentHandler.process(input);
}
}

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pipeline/src/main/java/com.iluwatar.pipeline/RemoveAlphabetsHandler.java Normal file
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/**
* The MIT License
* Copyright (c) 2014-2016 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.pipeline;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* Stage handler that returns a new instance of String without the alphabet characters of the input string.
*/
class RemoveAlphabetsHandler implements Handler<String, String> {
private final Logger logger = LoggerFactory.getLogger(RemoveAlphabetsHandler.class);
@Override
public String process(String input) {
StringBuilder inputWithoutAlphabets = new StringBuilder();
for (int index = 0; index < input.length(); index++) {
char currentCharacter = input.charAt(index);
if (Character.isAlphabetic(currentCharacter)) {
continue;
}
inputWithoutAlphabets.append(currentCharacter);
}
String inputWithoutAlphabetsStr = inputWithoutAlphabets.toString();
logger.info(String.format("Current handler: %s, input is %s of type %s, output is %s, of type %s",
RemoveAlphabetsHandler.class, input, String.class, inputWithoutAlphabetsStr, String.class));
return inputWithoutAlphabetsStr;
}
}

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pipeline/src/main/java/com.iluwatar.pipeline/RemoveDigitsHandler.java Normal file
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/**
* The MIT License
* Copyright (c) 2014-2016 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.pipeline;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* Stage handler that returns a new instance of String without the digit characters of the input string.
*/
class RemoveDigitsHandler implements Handler<String, String> {
private final Logger logger = LoggerFactory.getLogger(RemoveDigitsHandler.class);
@Override
public String process(String input) {
StringBuilder inputWithoutDigits = new StringBuilder();
for (int index = 0; index < input.length(); index++) {
char currentCharacter = input.charAt(index);
if (Character.isDigit(currentCharacter)) {
continue;
}
inputWithoutDigits.append(currentCharacter);
}
String inputWithoutDigitsStr = inputWithoutDigits.toString();
logger.info(String.format("Current handler: %s, input is %s of type %s, output is %s, of type %s",
RemoveDigitsHandler.class, input, String.class, inputWithoutDigitsStr, String.class));
return inputWithoutDigitsStr;
}
}

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/**
* The MIT License
* Copyright (c) 2014 Ilkka Seppälä
* <p>
* 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:
* <p>
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
* <p>
* 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.pipeline;
import org.junit.jupiter.api.Test;
/**
* Application Test
*/
public class AppTest {
@Test
public void test() {
String[] args = {};
App.main(args);
}
}

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/**
* The MIT License
* Copyright (c) 2014 Ilkka Seppälä
* <p>
* 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:
* <p>
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
* <p>
* 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.pipeline;
import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.assertArrayEquals;
/**
* Test for {@link Pipeline}
*/
public class PipelineTest {
@Test
public void testAddHandlersToPipeline() {
Pipeline<String, char[]> filters = new Pipeline<>(new RemoveAlphabetsHandler())
.addHandler(new RemoveDigitsHandler())
.addHandler(new ConvertToCharArrayHandler());
assertArrayEquals(
new char[] {'#', '!', '(', '&', '%', '#', '!'},
filters.execute("#H!E(L&L0O%THE3R#34E!")
);
}
}

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<module>property</module>
<module>intercepting-filter</module>
<module>producer-consumer</module>
<module>pipeline</module>
<module>poison-pill</module>
<module>reader-writer-lock</module>
<module>lazy-loading</module>