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basic implementation ++
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‎data-mapper/index.md‎

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---
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layout: pattern
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title: Data Mapper
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folder: data-mapper
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permalink: /patterns/dm/
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categories: Persistence Tier
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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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Object provides an abstract interface to some type of database or
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other persistence mechanism.
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![alt text](./etc/dm.png "Data Mapper")
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## Applicability
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Use the Data Mapper in any of the following situations
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* when you want to consolidate how the data layer is accessed
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* when you want to avoid writing multiple data retrieval/persistence layers
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## Credits
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* [Data Mapper](http://richard.jp.leguen.ca/tutoring/soen343-f2010/tutorials/implementing-data-mapper/)

‎data-mapper/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) 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
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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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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>1.11.0-SNAPSHOT</version>
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</parent>
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<artifactId>data-mapper</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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<build>
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<!--
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log4j.xml file will be copied both in ${project.build.outputDirectory}
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and ${project.build.directory}. Thanks to Sean Patrick Floyd
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(http://stackoverflow.com/questions/5637532/maven-how-to-place-resource-file-together-with-jar)
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-->
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<resources>
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<resource> <!-- regular processing for every resource file -->
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<directory>src/main/resources</directory>
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</resource>
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<resource> <!-- processing with a different output directory for log4j.xml -->
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<directory>src/main/resources</directory>
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<includes>
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<include>log4j.xml</include>
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</includes>
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<targetPath>..</targetPath> <!-- relative to target/classes i.e. ${project.build.directory} -->
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</resource>
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</resources>
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<plugins>
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<!--
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This will exclude log4j.xml file from generated JAR
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-->
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<plugin>
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<groupId>org.apache.maven.plugins</groupId>
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<artifactId>maven-jar-plugin</artifactId>
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<version>2.6</version>
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<configuration>
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<excludes>
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<exclude>log4j.xml</exclude>
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</excludes>
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<archive>
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<manifest>
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<addClasspath>true</addClasspath>
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</manifest>
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</archive>
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</configuration>
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</plugin>
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</plugins>
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</build>
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</project>

‎data-mapper/src/main/java/com/iluwatar/datamapper/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.datamapper;
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import java.util.Optional;
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import java.util.UUID;
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import org.apache.log4j.Logger;
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/**
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*
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* The Data Mapper (DM) is a layer of software that separates the in-memory objects from the
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* database. Its responsibility is to transfer data between the two and also to isolate them from
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* each other. With Data Mapper the in-memory objects needn't know even that there's a database
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* present; they need no SQL interface code, and certainly no knowledge of the database schema. (The
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* database schema is always ignorant of the objects that use it.) Since it's a form of Mapper ,
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* Data Mapper itself is even unknown to the domain layer.
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* <p>
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* The below example demonstrates basic CRUD operations: select, add, update, and delete.
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*
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*/
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public final class App {
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private static Logger log = Logger.getLogger(App.class);
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private static final String DB_TYPE_ORACLE = "Oracle";
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private static final String DB_TYPE_MYSQL = "MySQL";
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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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*/
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public static final void main(final String... args) {
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if (log.isInfoEnabled() & args.length > 0) {
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log.debug("App.main(), db type: " + args[0]);
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}
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StudentDataMapper mapper = null;
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/* Check the desired db type from runtime arguments */
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if (args.length == 0) {
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/* Create default data mapper for mysql */
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mapper = new StudentMySQLDataMapper();
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} else if (args.length > 0 && DB_TYPE_ORACLE.equalsIgnoreCase(args[0])) {
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/* Create new data mapper for mysql */
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mapper = new StudentMySQLDataMapper();
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} else if (args.length > 0 && DB_TYPE_MYSQL.equalsIgnoreCase(args[0])) {
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/* Create new data mapper for oracle */
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mapper = new StudentMySQLDataMapper();
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} else {
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/* Don't couple any Data Mapper to java.sql.SQLException */
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throw new DataMapperException("Following data source(" + args[0] + ") is not supported");
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}
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/* Create new student */
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Student student = new Student(UUID.randomUUID(), 1, "Adam", 'A');
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/* Add student in respectibe db */
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mapper.insert(student);
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/* Find this student */
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final Optional<Student> studentToBeFound = mapper.find(student.getGuId());
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if (log.isDebugEnabled()) {
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log.debug("App.main(), db find returned : " + studentToBeFound);
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}
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/* Update existing student object */
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student = new Student(student.getGuId(), 1, "AdamUpdated", 'A');
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/* Update student in respectibe db */
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mapper.update(student);
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/* Delete student in db */
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mapper.delete(student);
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}
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private App() {}
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}

‎data-mapper/src/main/java/com/iluwatar/datamapper/DataMapperException.java‎

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/**
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* The MIT License Copyright (c) 2016 Amit Dixit
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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.datamapper;
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/**
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*
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* @author amit.dixit
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*
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*/
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public final class DataMapperException extends RuntimeException {
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private static final long serialVersionUID = 1L;
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/**
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* Constructs a new runtime exception with {@code null} as its detail message. The cause is not
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* initialized, and may subsequently be initialized by a call to {@link #initCause}.
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*/
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public DataMapperException() {
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super();
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}
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/**
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* Constructs a new runtime exception with the specified detail message. The cause is not
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* initialized, and may subsequently be initialized by a call to {@link #initCause}.
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*
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* @param message the detail message. The detail message is saved for later retrieval by the
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* {@link #getMessage()} method.
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*/
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public DataMapperException(final String message) {
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super(message);
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}
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/**
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* Constructs a new runtime exception with the specified detail message and cause.
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* <p>
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* Note that the detail message associated with {@code cause} is <i>not</i> automatically
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* incorporated in this runtime exception's detail message.
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*
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* @param message the detail message (which is saved for later retrieval by the
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* {@link #getMessage()} method).
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* @param cause the cause (which is saved for later retrieval by the {@link #getCause()} method).
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* (A <tt>null</tt> value is permitted, and indicates that the cause is nonexistent or
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* unknown.)
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*/
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public DataMapperException(final String message, final Throwable cause) {
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super(message, cause);
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}
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/**
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* Constructs a new runtime exception with the specified cause and a detail message of
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* <tt>(cause==null ? null : cause.toString())</tt> (which typically contains the class and detail
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* message of <tt>cause</tt>). This constructor is useful for runtime exceptions that are little
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* more than wrappers for other throwables.
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*
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* @param cause the cause (which is saved for later retrieval by the {@link #getCause()} method).
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* (A <tt>null</tt> value is permitted, and indicates that the cause is nonexistent or
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* unknown.)
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*/
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public DataMapperException(final Throwable cause) {
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super(cause);
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}
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}

‎data-mapper/src/main/java/com/iluwatar/datamapper/Student.java‎

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/**
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* The MIT License Copyright (c) 2016 Amit Dixit
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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.datamapper;
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import java.io.Serializable;
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import java.util.UUID;
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public final class Student implements Serializable {
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private static final long serialVersionUID = 1L;
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private UUID guid;
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private int studentID;
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private String name;
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private char grade;
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public Student() {
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this.guid = UUID.randomUUID();
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}
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public Student(final UUID guid, final int studentID, final String name, final char grade) {
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super();
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this.guid = guid;
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this.studentID = studentID;
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this.name = name;
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this.grade = grade;
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}
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public Student(final UUID guid) {
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this.guid = guid;
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}
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public final int getStudentId() {
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return studentID;
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}
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public final void setStudentId(final int studentID) {
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this.studentID = studentID;
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}
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public final String getName() {
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return name;
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}
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public final void setName(final String name) {
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this.name = name;
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}
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public final char getGrade() {
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return grade;
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}
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public final void setGrade(final char grade) {
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this.grade = grade;
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}
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public final UUID getGuId() {
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return guid;
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}
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@Override
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public final String toString() {
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return "Student [guid=" + guid + ", studentID=" + studentID + ", name=" + name + ", grade=" + grade + "]";
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}
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}

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