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Amit Dixit
2016-10-26 16:59:36 +05:30
parent 19cb715d20
commit 2a77ac29e9
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---
layout: pattern
title: Module
folder: module
permalink: /patterns/module/
pumlid: JShB3OGm303HLg20nFVjnYGM1CN6ycTfVtFSsnjfzY5jPgUqkLqHwXy0mxUU8wuyqidQ8q4IjJqCO-QBWGOtVh5qyd5AKOmW4mT6Nu2-ZiAekapH_hkcSTNa-GC0
categories: Persistence Tier
tags:
- Java
- Difficulty-Beginner
---
## Intent
A layer of mappers that moves data between objects and a database while keeping them independent of each other and the mapper itself
![alt text](./etc/module.png "Module")
## Applicability
The module pattern is a design pattern used to implement the concept of software modules, defined by modular programming, in a programming language with incomplete direct support for the concept.
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.
It supports specific cases where a class or object can be considered structured, procedural data. And, vice versa, migrate structured, procedural data, and considered as object-oriented.
## Credits
* [Module](https://en.wikipedia.org/wiki/Module_pattern)

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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>

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module/src/main/java/com/iluwatar/module/App.java Normal file
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/**
* 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.
*/
package com.iluwatar.module;
import java.io.FileNotFoundException;
/**
* The Data Mapper (DM) is a layer of software that separates the in-memory
* objects from the database. Its responsibility is to transfer data between the
* two and also to isolate them from each other. With Data Mapper the in-memory
* objects needn't know even that there's a database present; they need no SQL
* interface code, and certainly no knowledge of the database schema. (The
* database schema is always ignorant of the objects that use it.) Since it's a
* form of Mapper , Data Mapper itself is even unknown to the domain layer.
* <p>
* The below example demonstrates basic CRUD operations: Create, Read, Update,
* and Delete.
*
*/
public final class App {
private static final String OUTPUT_FILE = "output.txt";
private static final String ERROR_FILE = "error.txt";
public static FilePrinterModule filePrinterModule = null;
public static void prepare() throws FileNotFoundException {
filePrinterModule = FilePrinterModule.getSingleton();
filePrinterModule.prepare(OUTPUT_FILE, ERROR_FILE);
}
public static void unprepare() {
filePrinterModule.unprepare();
}
public static final void execute(final String... args) {
filePrinterModule.printString("Hello World");
}
/**
* Program entry point.
*
* @param args
* command line args.
* @throws FileNotFoundException
*/
public static final void main(final String... args)
throws FileNotFoundException {
prepare();
execute(args);
unprepare();
}
private App() {
}
}

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module/src/main/java/com/iluwatar/module/FilePrinterModule.java Normal file
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package com.iluwatar.module;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.PrintStream;
import org.apache.log4j.Logger;
/**
* 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.
*/
public final class FilePrinterModule {
private static final Logger logger = Logger
.getLogger(FilePrinterModule.class);
private static FilePrinterModule singleton = null;
public PrintStream output = null;
public PrintStream error = null;
private FilePrinterModule() {
}
public static final FilePrinterModule getSingleton() {
if (FilePrinterModule.singleton == null) {
FilePrinterModule.singleton = new FilePrinterModule();
}
return FilePrinterModule.singleton;
}
/**
*
* @throws FileNotFoundException
*/
public final void prepare(final String outputFile, final String errorFile)
throws FileNotFoundException {
logger.debug("MainModule::prepare();");
this.output = new PrintStream(new FileOutputStream(outputFile));
this.error = new PrintStream(new FileOutputStream(errorFile));
}
/**
*
*/
public final void unprepare() {
if (this.output != null) {
this.output.flush();
this.output.close();
}
if (this.error != null) {
this.error.flush();
this.error.close();
}
logger.debug("MainModule::unprepare();");
}
/**
*
* @param value
*/
public final void printString(final String value) {
this.output.print(value);
}
/**
*
* @param value
*/
public final void printErrorString(final String value) {
this.error.print(value);
}
}

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<?xml version="1.0" encoding="UTF-8" ?>
<!--
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.
-->
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
<log4j:configuration debug="true"
xmlns:log4j='http://jakarta.apache.org/log4j/'>
<appender name="console" class="org.apache.log4j.ConsoleAppender">
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n" />
</layout>
</appender>
<root>
<level value="INFO" />
<appender-ref ref="console" />
</root>
</log4j:configuration>

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/**
* 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.
*/
package com.iluwatar.module;
import java.io.FileNotFoundException;
import com.iluwatar.module.App;
import org.junit.Test;
/**
* Tests that Data-Mapper example runs without errors.
*/
public final class AppTest {
@Test
public void test() throws FileNotFoundException {
final String[] args = {};
App.main(args);
}
}

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/**
* 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.
*/
package com.iluwatar.module;
import static org.junit.Assert.assertEquals;
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import org.apache.log4j.Logger;
import org.junit.Test;
/**
* The Data Mapper (DM) is a layer of software that separates the in-memory
* objects from the database. Its responsibility is to transfer data between the
* two and also to isolate them from each other. With Data Mapper the in-memory
* objects needn't know even that there's a database present; they need no SQL
* interface code, and certainly no knowledge of the database schema. (The
* database schema is always ignorant of the objects that use it.) Since it's a
* form of Mapper , Data Mapper itself is even unknown to the domain layer.
* <p>
*/
public class ModuleTest {
private static final Logger logger = Logger.getLogger(ModuleTest.class);
private static final String OUTPUT_FILE = "output.txt";
private static final String ERROR_FILE = "error.txt";
private static final String MESSAGE = "MESSAGE";
private static final String ERROR = "ERROR";
/**
* This test verify that 'MESSAGE' is perfectly printed in output file
*
* @throws IOException
*/
@Test
public void testPositiveMessage() throws IOException {
/* Prepare the essential sub modules, to perform the sequence of jobs */
final FilePrinterModule filePrinterModule = FilePrinterModule
.getSingleton();
/* Prepare the essential sub modules, to perform the sequence of jobs */
filePrinterModule.prepare(OUTPUT_FILE, ERROR_FILE);
/* Print 'Message' in file */
filePrinterModule.printString(MESSAGE);
/* Test if 'Message' is printed in file */
assertEquals(readFirstLine(OUTPUT_FILE), MESSAGE);
/* Unprepare to cleanup the modules */
filePrinterModule.unprepare();
}
/**
* This test verify that nothing is printed in output file
*
* @throws IOException
*/
@Test
public void testNegativeMessage() throws IOException {
/* Prepare the essential sub modules, to perform the sequence of jobs */
final FilePrinterModule filePrinterModule = FilePrinterModule
.getSingleton();
/* Prepare the essential sub modules, to perform the sequence of jobs */
filePrinterModule.prepare(OUTPUT_FILE, ERROR_FILE);
/* Test if nothing is printed in file */
assertEquals(readFirstLine(OUTPUT_FILE), null);
/* Unprepare to cleanup the modules */
filePrinterModule.unprepare();
}
/**
* This test verify that 'ERROR' is perfectly printed in error file
*
* @throws FileNotFoundException
*/
@Test
public void testPositiveErrorMessage() throws FileNotFoundException {
/* Prepare the essential sub modules, to perform the sequence of jobs */
final FilePrinterModule filePrinterModule = FilePrinterModule
.getSingleton();
/* Prepare the essential sub modules, to perform the sequence of jobs */
filePrinterModule.prepare(OUTPUT_FILE, ERROR_FILE);
/* Print 'Error' in file */
filePrinterModule.printErrorString(ERROR);
/* Test if 'Message' is printed in file */
assertEquals(readFirstLine(ERROR_FILE), ERROR);
/* Unprepare to cleanup the modules */
filePrinterModule.unprepare();
}
/**
* This test verify that nothing is printed in error file
*
* @throws FileNotFoundException
*/
@Test
public void testNegativeErrorMessage() throws FileNotFoundException {
/* Prepare the essential sub modules, to perform the sequence of jobs */
final FilePrinterModule filePrinterModule = FilePrinterModule
.getSingleton();
/* Prepare the essential sub modules, to perform the sequence of jobs */
filePrinterModule.prepare(OUTPUT_FILE, ERROR_FILE);
/* Test if nothing is printed in file */
assertEquals(readFirstLine(ERROR_FILE), null);
/* Unprepare to cleanup the modules */
filePrinterModule.unprepare();
}
/**
* Utility method to read first line of a file
*
* @param file
* @return
*/
private static final String readFirstLine(final String file) {
String firstLine = null;
BufferedReader bufferedReader = null;
try {
/* Create a buffered reader */
bufferedReader = new BufferedReader(new FileReader(file));
/* Read the line */
firstLine = bufferedReader.readLine();
logger.info("ModuleTest::readFile() : firstLine : " + firstLine);
} catch (final IOException e) {
logger.error("ModuleTest::readFile()", e);
} finally {
if (bufferedReader != null) {
try {
bufferedReader.close();
} catch (final IOException e) {
logger.error("ModuleTest::readFile()", e);
}
}
}
return firstLine;
}
}