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‎chain/README.md‎

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@@ -16,7 +16,131 @@ Avoid coupling the sender of a request to its receiver by giving
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more than one object a chance to handle the request. Chain the receiving
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objects and pass the request along the chain until an object handles it.
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![alt text](./etc/chain_1.png "Chain of Responsibility")
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## Explanation
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Real world example
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> The Orc King gives loud orders to his army. The closest one to react is the commander, then officer and then soldier. The commander, officer and soldier here form a chain of responsibility.
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In plain words
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> It helps building a chain of objects. Request enters from one end and keeps going from object to object till it finds the suitable handler.
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Wikipedia says
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> In object-oriented design, the chain-of-responsibility pattern is a design pattern consisting of a source of command objects and a series of processing objects. Each processing object contains logic that defines the types of command objects that it can handle; the rest are passed to the next processing object in the chain.
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**Programmatic Example**
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Translating our example with orcs from above. First we have the request class
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```
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public class Request {
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private final RequestType requestType;
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private final String requestDescription;
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private boolean handled;
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public Request(final RequestType requestType, final String requestDescription) {
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this.requestType = Objects.requireNonNull(requestType);
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this.requestDescription = Objects.requireNonNull(requestDescription);
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}
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public String getRequestDescription() { return requestDescription; }
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public RequestType getRequestType() { return requestType; }
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public void markHandled() { this.handled = true; }
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public boolean isHandled() { return this.handled; }
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@Override
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public String toString() { return getRequestDescription(); }
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}
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public enum RequestType {
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DEFEND_CASTLE, TORTURE_PRISONER, COLLECT_TAX
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}
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```
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Then the request handler hierarchy
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```
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public abstract class RequestHandler {
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private static final Logger LOGGER = LoggerFactory.getLogger(RequestHandler.class);
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private RequestHandler next;
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public RequestHandler(RequestHandler next) {
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this.next = next;
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}
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public void handleRequest(Request req) {
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if (next != null) {
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next.handleRequest(req);
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}
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}
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protected void printHandling(Request req) {
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LOGGER.info("{} handling request \"{}\"", this, req);
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}
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@Override
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public abstract String toString();
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}
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public class OrcCommander extends RequestHandler {
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public OrcCommander(RequestHandler handler) {
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super(handler);
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}
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@Override
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public void handleRequest(Request req) {
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if (req.getRequestType().equals(RequestType.DEFEND_CASTLE)) {
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printHandling(req);
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req.markHandled();
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} else {
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super.handleRequest(req);
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}
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}
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@Override
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public String toString() {
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return "Orc commander";
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}
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}
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// OrcOfficer and OrcSoldier are defined similarly as OrcCommander
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```
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Then we have the Orc King who gives the orders and forms the chain
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```
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public class OrcKing {
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RequestHandler chain;
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public OrcKing() {
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buildChain();
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}
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private void buildChain() {
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chain = new OrcCommander(new OrcOfficer(new OrcSoldier(null)));
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}
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public void makeRequest(Request req) {
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chain.handleRequest(req);
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}
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}
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```
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Then it is used as follows
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```
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OrcKing king = new OrcKing();
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king.makeRequest(new Request(RequestType.DEFEND_CASTLE, "defend castle")); // Orc commander handling request "defend castle"
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king.makeRequest(new Request(RequestType.TORTURE_PRISONER, "torture prisoner")); // Orc officer handling request "torture prisoner"
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king.makeRequest(new Request(RequestType.COLLECT_TAX, "collect tax")); // Orc soldier handling request "collect tax"
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```
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## Applicability
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Use Chain of Responsibility when

‎chain/etc/chain.png‎

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‎chain/etc/chain.ucls‎

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‎chain/etc/chain.urm.puml‎

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‎chain/etc/chain_1.png‎

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‎checkstyle.xml‎

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value="LITERAL_TRY, LITERAL_CATCH, LITERAL_FINALLY, LITERAL_IF, LITERAL_ELSE, LITERAL_SWITCH"/>
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</module>
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<module name="NeedBraces"/>
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<module name="LeftCurly">
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<property name="maxLineLength" value="120"/>
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</module>
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<module name="LeftCurly"/>
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<module name="RightCurly"/>
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<module name="RightCurly">
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<property name="option" value="alone"/>

‎dao/src/main/java/com/iluwatar/dao/CustomException.java‎

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/**
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* The MIT License
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* Copyright (c) 2014 Ilkka Seppälä
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*
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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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*
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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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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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package com.iluwatar.dao;
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/**
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*
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* Custom exception
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*
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*/
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public class CustomException extends Exception {
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private static final long serialVersionUID = 1L;
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public CustomException() {}
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public CustomException(String message) {
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super(message);
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}
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public CustomException(String message, Throwable cause) {
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super(message, cause);
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}
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}

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