Module pattern #62

module/README.md

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+---
+layout: pattern
+title: Module
+folder: module
+permalink: /patterns/module/
+pumlid: JShB3OGm303HLg20nFVjnYGM1CN6ycTfVtFSsnjfzY5jPgUqkLqHwXy0mxUU8wuyqidQ8q4IjJqCO-QBWGOtVh5qyd5AKOmW4mT6Nu2-ZiAekapH_hkcSTNa-GC0
+categories: Creational Pattern
+tags:
+ - Java
+ - Difficulty-Beginner
+---
+
+## Intent
+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.
+
+![alt text](./etc/module.png "Module")
+
+## Applicability
+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.
+
+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.
+
+## Credits
+
+* [Module](https://en.wikipedia.org/wiki/Module_pattern)

module/etc/module.ucls

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

module/etc/module.urm.puml

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

module/pom.xml

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+<?xml version="1.0"?>
+<!--
+
+    The MIT License
+    Copyright (c) 2016 Amit Dixit
+
+    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>1.14.0-SNAPSHOT</version>
+	</parent>
+	<artifactId>module</artifactId>
+	<dependencies>
+		<dependency>
+			<groupId>junit</groupId>
+			<artifactId>junit</artifactId>
+			<scope>test</scope>
+		</dependency>
+		<dependency>
+			<groupId>log4j</groupId>
+			<artifactId>log4j</artifactId>
+		</dependency>
+	</dependencies>
+</project>

module/src/main/java/com/iluwatar/module/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.module;
+
+import java.io.FileNotFoundException;
+
+/**
+ * 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.
+ * 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.
+ * <p>
+ * The below example demonstrates a use case for testing two different modules: File Logger and
+ * Console Logger
+ * 
+ */
+public final class App {
+
+  public static FileLoggerModule fileLoggerModule;
+  public static ConsoleLoggerModule consoleLoggerModule;
+
+  /**
+   * Following method performs the initialization
+   * 
+   * @throws FileNotFoundException if program is not able to find log files (output.txt and
+   *         error.txt)
+   */
+  public static void prepare() throws FileNotFoundException {
+
+    /* Create new singleton objects and prepare their modules */
+    fileLoggerModule = FileLoggerModule.getSingleton().prepare();
+    consoleLoggerModule = ConsoleLoggerModule.getSingleton().prepare();
+  }
+
+  /**
+   * Following method performs the finalization
+   */
+  public static void unprepare() {
+
+    /* Close all resources */
+    fileLoggerModule.unprepare();
+    consoleLoggerModule.unprepare();
+  }
+
+  /**
+   * Following method is main executor
+   * 
+   * @param args for providing default program arguments
+   */
+  public static void execute(final String... args) {
+
+    /* Send logs on file system */
+    fileLoggerModule.printString("Message");
+    fileLoggerModule.printErrorString("Error");
+
+    /* Send logs on console */
+    consoleLoggerModule.printString("Message");
+    consoleLoggerModule.printErrorString("Error");
+  }
+
+  /**
+   * Program entry point.
+   * 
+   * @param args command line args.
+   * @throws FileNotFoundException if program is not able to find log files (output.txt and
+   *         error.txt)
+   */
+  public static void main(final String... args) throws FileNotFoundException {
+    prepare();
+    execute(args);
+    unprepare();
+  }
+
+  private App() {}
+}

module/src/main/java/com/iluwatar/module/ConsoleLoggerModule.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.module;
+
+import java.io.PrintStream;
+
+import org.apache.log4j.Logger;
+
+/**
+ * The ConsoleLoggerModule is responsible for showing logs on System Console
+ * <p>
+ * The below example demonstrates a Console logger module, which can print simple and error messages
+ * in two designated formats
+ */
+public final class ConsoleLoggerModule {
+
+  private static final Logger LOGGER = Logger.getLogger(ConsoleLoggerModule.class);
+
+  private static ConsoleLoggerModule singleton = null;
+
+  public PrintStream output = null;
+  public PrintStream error = null;
+
+  private ConsoleLoggerModule() {}
+
+  /**
+   * Static method to get single instance of class
+   * 
+   * @return singleton instance of ConsoleLoggerModule
+   */
+  public static ConsoleLoggerModule getSingleton() {
+
+    if (ConsoleLoggerModule.singleton == null) {
+      ConsoleLoggerModule.singleton = new ConsoleLoggerModule();
+    }
+
+    return ConsoleLoggerModule.singleton;
+  }
+
+  /**
+   * Following method performs the initialization
+   */
+  public ConsoleLoggerModule prepare() {
+
+    LOGGER.debug("ConsoleLoggerModule::prepare();");
+
+    this.output = new PrintStream(System.out);
+    this.error = new PrintStream(System.err);
+
+    return this;
+  }
+
+  /**
+   * Following method performs the finalization
+   */
+  public void unprepare() {
+
+    if (this.output != null) {
+
+      this.output.flush();
+      this.output.close();
+    }
+
+    if (this.error != null) {
+
+      this.error.flush();
+      this.error.close();
+    }
+
+    LOGGER.debug("ConsoleLoggerModule::unprepare();");
+  }
+
+  /**
+   * Used to print a message
+   * 
+   * @param value will be printed on console
+   */
+  public void printString(final String value) {
+    this.output.println(value);
+  }
+
+  /**
+   * Used to print a error message
+   * 
+   * @param value will be printed on error console
+   */
+  public void printErrorString(final String value) {
+    this.error.println(value);
+  }
+}