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Module pattern iluwatar#62
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‎module/README.md

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---
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layout: pattern
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title: Module
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folder: module
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permalink: /patterns/module/
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pumlid: JShB3OGm303HLg20nFVjnYGM1CN6ycTfVtFSsnjfzY5jPgUqkLqHwXy0mxUU8wuyqidQ8q4IjJqCO-QBWGOtVh5qyd5AKOmW4mT6Nu2-ZiAekapH_hkcSTNa-GC0
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categories: Creational Pattern
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tags:
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- Java
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- Difficulty-Beginner
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---
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## Intent
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Module pattern is used to implement the concept of software modules, defined by modular programming, in a programming language with incomplete direct support for the concept.
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![alt text](./etc/module.png "Module")
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## Applicability
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The Module pattern can be considered a creational pattern and a structural pattern. It manages the creation and organization of other elements, and groups them as the structural pattern does.
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An object that applies this pattern can provide the equivalent of a namespace, providing the initialization and finalization process of a static class or a class with static members with cleaner, more concise syntax and semantics.
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## Credits
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* [Module](https://en.wikipedia.org/wiki/Module_pattern)

‎module/etc/module.png

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‎module/etc/module.ucls

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<?xml version="1.0" encoding="UTF-8"?>
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<class-diagram version="1.1.9" icons="true" always-add-relationships="false" generalizations="true" realizations="true"
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associations="true" dependencies="false" nesting-relationships="true" router="FAN">
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<class id="1" language="java" name="com.iluwatar.module.FileLoggerModule" project="module"
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file="/module/src/main/java/com/iluwatar/module/FileLoggerModule.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="401" y="190"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" 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="2" language="java" name="com.iluwatar.module.ConsoleLoggerModule" project="module"
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file="/module/src/main/java/com/iluwatar/module/ConsoleLoggerModule.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="686" y="176"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" 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.module.App" project="module"
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file="/module/src/main/java/com/iluwatar/module/App.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="558" y="501"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" 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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<association id="4">
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<end type="SOURCE" refId="1" navigable="false">
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<attribute id="5" name="singleton"/>
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<multiplicity id="6" minimum="0" maximum="1"/>
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</end>
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<end type="TARGET" refId="1" navigable="true"/>
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<display labels="true" multiplicity="true"/>
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</association>
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<association id="7">
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<end type="SOURCE" refId="2" navigable="false">
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<attribute id="8" name="singleton"/>
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<multiplicity id="9" minimum="0" maximum="1"/>
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</end>
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<end type="TARGET" refId="2" navigable="true"/>
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<display labels="true" multiplicity="true"/>
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</association>
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<association id="10">
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<end type="SOURCE" refId="3" navigable="false">
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<attribute id="11" name="consoleLoggerModule"/>
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<multiplicity id="12" minimum="0" maximum="1"/>
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</end>
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<end type="TARGET" refId="2" navigable="true"/>
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<display labels="true" multiplicity="true"/>
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</association>
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<association id="13">
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<end type="SOURCE" refId="3" navigable="false">
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<attribute id="14" name="fileLoggerModule"/>
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<multiplicity id="15" minimum="0" maximum="1"/>
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</end>
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<end type="TARGET" refId="1" navigable="true"/>
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<display labels="true" multiplicity="true"/>
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</association>
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<classifier-display autosize="true" stereotype="true" package="true" initial-value="false" 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>

‎module/etc/module.urm.puml

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@startuml
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package com.iluwatar.module {
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class App {
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+ consoleLoggerModule : ConsoleLoggerModule {static}
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+ fileLoggerModule : FileLoggerModule {static}
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- App()
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+ execute(args : String[]) {static}
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+ main(args : String[]) {static}
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+ prepare() {static}
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+ unprepare() {static}
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}
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class ConsoleLoggerModule {
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- LOGGER : Logger {static}
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+ error : PrintStream
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+ output : PrintStream
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- singleton : ConsoleLoggerModule {static}
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- ConsoleLoggerModule()
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+ getSingleton() : ConsoleLoggerModule {static}
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+ prepare()
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+ printErrorString(value : String)
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+ printString(value : String)
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+ unprepare()
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}
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class FileLoggerModule {
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- ERROR_FILE : String {static}
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- LOGGER : Logger {static}
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- OUTPUT_FILE : String {static}
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+ error : PrintStream
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+ output : PrintStream
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- singleton : FileLoggerModule {static}
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- FileLoggerModule()
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+ getSingleton() : FileLoggerModule {static}
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+ prepare()
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+ printErrorString(value : String)
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+ printString(value : String)
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+ unprepare()
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}
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}
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FileLoggerModule --> "-singleton" FileLoggerModule
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App --> "-consoleLoggerModule" ConsoleLoggerModule
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ConsoleLoggerModule --> "-singleton" ConsoleLoggerModule
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App --> "-fileLoggerModule" FileLoggerModule
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@enduml

‎module/pom.xml

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<?xml version="1.0"?>
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<!--
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The MIT License
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Copyright (c) 2016 Amit Dixit
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Permission is hereby granted, free of charge, to any person obtaining a copy
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of this software and associated documentation files (the "Software"), to deal
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in the Software without restriction, including without limitation the rights
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to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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copies of the Software, and to permit persons to whom the Software is
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furnished to do so, subject to the following conditions:
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The above copyright notice and this permission notice shall be included in
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all copies or substantial portions of the Software.
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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THE SOFTWARE.
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-->
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<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
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<modelVersion>4.0.0</modelVersion>
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<parent>
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<groupId>com.iluwatar</groupId>
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<artifactId>java-design-patterns</artifactId>
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<version>1.14.0-SNAPSHOT</version>
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</parent>
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<artifactId>module</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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<dependency>
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<groupId>log4j</groupId>
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<artifactId>log4j</artifactId>
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</dependency>
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</dependencies>
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</project>

‎module/src/main/java/com/iluwatar/module/App.java

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/**
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* The MIT License Copyright (c) 2014 Ilkka Seppälä
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy of this software and
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* associated documentation files (the "Software"), to deal in the Software without restriction,
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* including without limitation the rights to use, copy, modify, merge, publish, distribute,
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* sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in all copies or
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* substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT
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* NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
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* DAMAGES OR OTHER 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 THE SOFTWARE.
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*/
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package com.iluwatar.module;
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import java.io.FileNotFoundException;
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/**
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* The Module pattern can be considered a Creational pattern and a Structural pattern. It manages
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* the creation and organization of other elements, and groups them as the structural pattern does.
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* An object that applies this pattern can provide the equivalent of a namespace, providing the
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* initialization and finalization process of a static class or a class with static members with
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* cleaner, more concise syntax and semantics.
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* <p>
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* The below example demonstrates a use case for testing two different modules: File Logger and
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* Console Logger
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*
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*/
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public final class App {
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public static FileLoggerModule fileLoggerModule;
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public static ConsoleLoggerModule consoleLoggerModule;
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/**
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* Following method performs the initialization
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*
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* @throws FileNotFoundException if program is not able to find log files (output.txt and
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* error.txt)
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*/
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public static void prepare() throws FileNotFoundException {
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/* Create new singleton objects and prepare their modules */
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fileLoggerModule = FileLoggerModule.getSingleton().prepare();
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consoleLoggerModule = ConsoleLoggerModule.getSingleton().prepare();
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}
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/**
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* Following method performs the finalization
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*/
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public static void unprepare() {
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/* Close all resources */
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fileLoggerModule.unprepare();
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consoleLoggerModule.unprepare();
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}
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/**
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* Following method is main executor
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*
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* @param args for providing default program arguments
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*/
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public static void execute(final String... args) {
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/* Send logs on file system */
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fileLoggerModule.printString("Message");
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fileLoggerModule.printErrorString("Error");
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/* Send logs on console */
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consoleLoggerModule.printString("Message");
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consoleLoggerModule.printErrorString("Error");
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}
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/**
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* Program entry point.
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*
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* @param args command line args.
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* @throws FileNotFoundException if program is not able to find log files (output.txt and
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* error.txt)
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*/
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public static void main(final String... args) throws FileNotFoundException {
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prepare();
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execute(args);
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unprepare();
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}
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private App() {}
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}

‎module/src/main/java/com/iluwatar/module/ConsoleLoggerModule.java

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/**
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* The MIT License Copyright (c) 2014 Ilkka Seppälä
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy of this software and
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* associated documentation files (the "Software"), to deal in the Software without restriction,
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* including without limitation the rights to use, copy, modify, merge, publish, distribute,
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* sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in all copies or
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* substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT
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* NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
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* DAMAGES OR OTHER 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 THE SOFTWARE.
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*/
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package com.iluwatar.module;
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import java.io.PrintStream;
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import org.apache.log4j.Logger;
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/**
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* The ConsoleLoggerModule is responsible for showing logs on System Console
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* <p>
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* The below example demonstrates a Console logger module, which can print simple and error messages
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* in two designated formats
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*/
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public final class ConsoleLoggerModule {
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private static final Logger LOGGER = Logger.getLogger(ConsoleLoggerModule.class);
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private static ConsoleLoggerModule singleton = null;
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public PrintStream output = null;
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public PrintStream error = null;
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private ConsoleLoggerModule() {}
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/**
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* Static method to get single instance of class
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*
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* @return singleton instance of ConsoleLoggerModule
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*/
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public static ConsoleLoggerModule getSingleton() {
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if (ConsoleLoggerModule.singleton == null) {
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ConsoleLoggerModule.singleton = new ConsoleLoggerModule();
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}
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return ConsoleLoggerModule.singleton;
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}
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/**
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* Following method performs the initialization
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*/
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public ConsoleLoggerModule prepare() {
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LOGGER.debug("ConsoleLoggerModule::prepare();");
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this.output = new PrintStream(System.out);
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this.error = new PrintStream(System.err);
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return this;
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}
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/**
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* Following method performs the finalization
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*/
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public void unprepare() {
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if (this.output != null) {
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this.output.flush();
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this.output.close();
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}
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if (this.error != null) {
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this.error.flush();
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this.error.close();
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}
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LOGGER.debug("ConsoleLoggerModule::unprepare();");
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}
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/**
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* Used to print a message
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*
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* @param value will be printed on console
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*/
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public void printString(final String value) {
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this.output.println(value);
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}
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/**
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* Used to print a error message
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*
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* @param value will be printed on error console
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*/
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public void printErrorString(final String value) {
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this.error.println(value);
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}
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}

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