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Merge pull request iluwatar#367 from mikulucky/master
Feature Toogle PR
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‎feature-toggle/etc/feature-toggle.png‎

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‎feature-toggle/etc/feature-toggle.ucls‎

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<?xml version="1.0" encoding="UTF-8"?>
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<class-diagram version="1.1.9" icons="true" automaticImage="PNG" always-add-relationships="true" generalizations="true"
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realizations="true" associations="true" dependencies="true" nesting-relationships="true" router="FAN">
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<interface id="1" language="java" name="com.iluwatar.featuretoggle.pattern.Service" project="feature-toggle"
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file="/feature-toggle/src/main/java/com/iluwatar/featuretoggle/pattern/Service.java" binary="false"
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corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="238" y="187"/>
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<display autosize="true" stereotype="true" package="true" initial-value="true" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</interface>
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<class id="2" language="java"
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name="com.iluwatar.featuretoggle.pattern.propertiesversion.PropertiesFeatureToggleVersion" project="feature-toggle"
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file="/feature-toggle/src/main/java/com/iluwatar/featuretoggle/pattern/propertiesversion/PropertiesFeatureToggleVersion.java"
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binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="241" y="449"/>
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<display autosize="true" stereotype="true" package="true" initial-value="true" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</class>
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<class id="3" language="java" name="com.iluwatar.featuretoggle.pattern.tieredversion.TieredFeatureToggleVersion"
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project="feature-toggle"
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file="/feature-toggle/src/main/java/com/iluwatar/featuretoggle/pattern/tieredversion/TieredFeatureToggleVersion.java"
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binary="false" corner="BOTTOM_RIGHT">
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<position height="149" width="230" x="502" y="119"/>
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<display autosize="false" stereotype="true" package="true" initial-value="true" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</class>
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<class id="4" language="java" name="com.iluwatar.featuretoggle.user.User" project="feature-toggle"
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file="/feature-toggle/src/main/java/com/iluwatar/featuretoggle/user/User.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="616" y="453"/>
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<display autosize="true" stereotype="true" package="true" initial-value="true" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</class>
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<class id="5" language="java" name="com.iluwatar.featuretoggle.user.UserGroup" project="feature-toggle"
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file="/feature-toggle/src/main/java/com/iluwatar/featuretoggle/user/UserGroup.java" binary="false"
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corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="956" y="187"/>
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<display autosize="true" stereotype="true" package="true" initial-value="true" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</class>
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<dependency id="6">
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<end type="SOURCE" refId="1"/>
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<end type="TARGET" refId="4"/>
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</dependency>
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<dependency id="7">
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<end type="SOURCE" refId="3"/>
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<end type="TARGET" refId="5"/>
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</dependency>
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<association id="8">
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<bendpoint x="911" y="415"/>
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<end type="SOURCE" refId="5" navigable="false">
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<attribute id="9" name="freeGroup">
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<position height="19" width="63" x="846" y="368"/>
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</attribute>
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<multiplicity id="10" minimum="0" maximum="2147483647">
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<position height="17" width="23" x="707" y="418"/>
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</multiplicity>
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</end>
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<end type="TARGET" refId="4" navigable="true"/>
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<display labels="true" multiplicity="true"/>
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</association>
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<realization id="11">
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<end type="SOURCE" refId="2"/>
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<end type="TARGET" refId="1"/>
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</realization>
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<dependency id="12">
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<end type="SOURCE" refId="2"/>
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<end type="TARGET" refId="4"/>
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</dependency>
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<dependency id="13">
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<end type="SOURCE" refId="3"/>
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<end type="TARGET" refId="4"/>
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</dependency>
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<association id="14">
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<bendpoint x="953" y="459"/>
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<end type="SOURCE" refId="5" navigable="false">
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<attribute id="15" name="paidGroup">
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<position height="19" width="66" x="963" y="419"/>
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</attribute>
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<multiplicity id="16" minimum="0" maximum="2147483647">
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<position height="17" width="23" x="711" y="463"/>
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</multiplicity>
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</end>
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<end type="TARGET" refId="4" navigable="true"/>
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<display labels="true" multiplicity="true"/>
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</association>
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<realization id="17">
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<end type="SOURCE" refId="3"/>
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<end type="TARGET" refId="1"/>
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</realization>
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<classifier-display autosize="true" stereotype="true" package="true" initial-value="true" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</classifier-display>
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<association-display labels="true" multiplicity="true"/>
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</class-diagram>

‎feature-toggle/index.md‎

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---
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layout: pattern
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title: Feature Toggle
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folder: feature-toggle
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permalink: /patterns/feature-toggle/
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categories: Behavioral
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tags:
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- Java
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- Difficulty-Beginner
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---
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## Also known as
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Feature Flag
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## Intent
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Used to switch code execution paths based on properties or groupings. Allowing new features to be released, tested
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and rolled out. Allowing switching back to the older feature quickly if needed. It should be noted that this pattern,
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can easily introduce code complexity. There is also cause for concern that the old feature that the toggle is eventually
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going to phase out is never removed, causing redundant code smells and increased maintainability.
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![alt text](./etc/feature-toggle.png "Feature Toggle")
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## Applicability
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Use the Feature Toogle pattern when
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* Giving different features to different users.
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* Rolling out a new feature incrementally.
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* Switching between development and production environments.
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## Credits
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* [Martin Fowler 29 October 2010 (2010-10-29).](http://martinfowler.com/bliki/FeatureToggle.html)

‎feature-toggle/pom.xml‎

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<?xml version="1.0" encoding="UTF-8"?>
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<!--
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The MIT License
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Copyright (c) 2014 Ilkka Seppälä
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Permission is hereby granted, free of charge, to any person obtaining a copy
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of this software and associated documentation files (the "Software"), to deal
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in the Software without restriction, including without limitation the rights
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to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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copies of the Software, and to permit persons to whom the Software is
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furnished to do so, subject to the following conditions:
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The above copyright notice and this permission notice shall be included in
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all copies or substantial portions of the Software.
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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THE SOFTWARE.
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-->
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<project xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xmlns="http://maven.apache.org/POM/4.0.0"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<parent>
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<artifactId>java-design-patterns</artifactId>
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<groupId>com.iluwatar</groupId>
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<version>1.10.0-SNAPSHOT</version>
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</parent>
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<modelVersion>4.0.0</modelVersion>
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<artifactId>feature-toggle</artifactId>
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<dependencies>
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<dependency>
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<groupId>junit</groupId>
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<artifactId>junit</artifactId>
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<scope>test</scope>
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</dependency>
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</dependencies>
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</project>

‎feature-toggle/src/main/java/com/iluwatar/featuretoggle/App.java‎

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/**
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* The MIT License
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* Copyright (c) 2014 Ilkka Seppälä
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* <p>
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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* <p>
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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* <p>
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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package com.iluwatar.featuretoggle;
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import com.iluwatar.featuretoggle.pattern.Service;
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import com.iluwatar.featuretoggle.pattern.propertiesversion.PropertiesFeatureToggleVersion;
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import com.iluwatar.featuretoggle.user.User;
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import com.iluwatar.featuretoggle.user.UserGroup;
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import java.util.Properties;
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/**
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* The Feature Toggle pattern allows for complete code executions to be turned on or off with ease. This allows features
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* to be controlled by either dynamic methods just as {@link User} information or by {@link Properties}. In the App
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* below there are two examples. Firstly the {@link Properties} version of the feature toggle, where the enhanced
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* version of the welcome message which is personalised is turned either on or off at instance creation. This method
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* is not as dynamic as the {@link User} driven version where the feature of the personalised welcome message is
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* dependant on the {@link UserGroup} the {@link User} is in. So if the user is a memeber of the
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* {@link UserGroup#isPaid(User)} then they get an ehanced version of the welcome message.
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*
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* Note that this pattern can easily introduce code complexity, and if not kept in check can result in redundant
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* unmaintained code within the codebase.
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*
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*/
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public class App {
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/**
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* Block 1 shows the {@link PropertiesFeatureToggleVersion} being run with {@link Properties} setting the feature
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* toggle to enabled.
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*
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* Block 2 shows the {@link PropertiesFeatureToggleVersion} being run with {@link Properties} setting the feature
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* toggle to disabled. Notice the difference with the printed welcome message the username is not included.
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*
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* Block 3 shows the {@link com.iluwatar.featuretoggle.pattern.tieredversion.TieredFeatureToggleVersion} being
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* set up with two users on who is on the free level, while the other is on the paid level. When the
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* {@link Service#getWelcomeMessage(User)} is called with the paid {@link User} note that the welcome message
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* contains their username, while the same service call with the free tier user is more generic. No username is
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* printed.
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*
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* @see User
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* @see UserGroup
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* @see Service
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* @see PropertiesFeatureToggleVersion
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* @see com.iluwatar.featuretoggle.pattern.tieredversion.TieredFeatureToggleVersion;
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*/
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public static void main(String[] args) {
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final Properties properties = new Properties();
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properties.put("enhancedWelcome", true);
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Service service = new PropertiesFeatureToggleVersion(properties);
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final String welcomeMessage = service.getWelcomeMessage(new User("Jamie No Code"));
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System.out.println(welcomeMessage);
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// ---------------------------------------------
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final Properties turnedOff = new Properties();
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turnedOff.put("enhancedWelcome", false);
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Service turnedOffService = new PropertiesFeatureToggleVersion(turnedOff);
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final String welcomeMessageturnedOff = turnedOffService.getWelcomeMessage(new User("Jamie No Code"));
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System.out.println(welcomeMessageturnedOff);
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// --------------------------------------------
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final User paidUser = new User("Jamie Coder");
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final User freeUser = new User("Alan Defect");
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UserGroup.addUserToPaidGroup(paidUser);
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UserGroup.addUserToFreeGroup(freeUser);
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final String welcomeMessagePaidUser = service.getWelcomeMessage(paidUser);
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final String welcomeMessageFreeUser = service.getWelcomeMessage(freeUser);
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System.out.println(welcomeMessageFreeUser);
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System.out.println(welcomeMessagePaidUser);
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}
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}

‎feature-toggle/src/main/java/com/iluwatar/featuretoggle/pattern/Service.java‎

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/**
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* The MIT License
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* Copyright (c) 2014 Ilkka Seppälä
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* <p>
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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* <p>
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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* <p>
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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package com.iluwatar.featuretoggle.pattern;
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import com.iluwatar.featuretoggle.user.User;
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/**
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* Simple interfaces to allow the calling of the method to generate the welcome message for a given user. While there is
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* a helper method to gather the the status of the feature toggle. In some cases there is no need for the
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* {@link Service#isEnhanced()} in {@link com.iluwatar.featuretoggle.pattern.tieredversion.TieredFeatureToggleVersion}
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* where the toggle is determined by the actual {@link User}.
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*
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* @see com.iluwatar.featuretoggle.pattern.propertiesversion.PropertiesFeatureToggleVersion
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* @see com.iluwatar.featuretoggle.pattern.tieredversion.TieredFeatureToggleVersion
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* @see User
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*/
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public interface Service {
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/**
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* Generates a welcome message for the passed user.
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*
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* @param user the {@link User} to be used if the message is to be personalised.
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* @return Generated {@link String} welcome message
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*/
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String getWelcomeMessage(User user);
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/**
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* Returns if the welcome message to be displayed will be the enhanced version.
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*
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* @return Boolean {@value true} if enhanced.
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*/
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boolean isEnhanced();
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}

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