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ahucoderahucoder
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Merge pull request #8 from ahucoder/dev
The Chain of Responsibility Pattern
2 parents 8253ccb + 3bb43ce commit 61c0bb5

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‎src/main/java/chain/App.java‎

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package chain;
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import chain.dto.ApprovalRequestDto;
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import chain.enums.RequestType;
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import chain.handler.ApprovalHandler;
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import chain.processor.CEO;
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import chain.processor.DepartmentManager;
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import chain.processor.HRManager;
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public class App {
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public static void main(String[] args) {
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// Chain：deptManager -> hrManager -> CEO
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ApprovalHandler deptManager = new DepartmentManager();
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ApprovalHandler hrManager = new HRManager();
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ApprovalHandler ceo = new CEO();
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deptManager.linkWith(hrManager).linkWith(ceo);
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// Different scene requests
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ApprovalRequestDto r1 = new ApprovalRequestDto(RequestType.LEAVE, "Alice", 0, 2);
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ApprovalRequestDto r2 = new ApprovalRequestDto(RequestType.EXPENSE, "Bob", 800, 0);
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ApprovalRequestDto r3 = new ApprovalRequestDto(RequestType.PURCHASE, "Charlie", 5000, 0);
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ApprovalRequestDto r4 = new ApprovalRequestDto(RequestType.LEAVE, "David", 0, 10);
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System.out.println("--- Start processing requests ---");
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System.out.printf("--- r1 start [%s]---%n", r1.getType());
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deptManager.handle(r1);
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System.out.printf("--- r1 end [%s]---%n", r1.getType());
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System.out.printf("--- r2 start [%s]---%n", r2.getType());
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deptManager.handle(r2);
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System.out.printf("--- r2 end [%s]---%n", r2.getType());
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System.out.printf("--- r3 start [%s]---%n", r3.getType());
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deptManager.handle(r3);
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System.out.printf("--- r3 end [%s]---%n", r3.getType());
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System.out.printf("--- r4 start [%s]---%n", r4.getType());
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deptManager.handle(r4);
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System.out.printf("--- r4 end [%s]---%n", r4.getType());
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System.out.println("--- Request processing completed ---");
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}
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}

‎src/main/java/chain/dto/ApprovalRequestDto.java‎

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package chain.dto;
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import chain.enums.RequestType;
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import lombok.AllArgsConstructor;
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import lombok.Getter;
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@AllArgsConstructor
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@Getter
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public class ApprovalRequestDto {
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private final RequestType type;
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private final String applicant;
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private final double amount;
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private final int days;
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}

‎src/main/java/chain/enums/RequestType.java‎

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package chain.enums;
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public enum RequestType {
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LEAVE("Leave Application"),
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EXPENSE("Expense Reimbursement "),
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PURCHASE("Procurement Request"),
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;
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private final String typeName;
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RequestType(String typeName) {
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this.typeName = typeName;
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}
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/**
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* Get a description of the type
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* @return description of the type
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*/
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public String getType() {
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return typeName;
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}
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/**
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* Search for the corresponding enumeration value based on the string (case-insensitive)
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* @param typeStr Type string
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* @return Corresponding enumeration values
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* @throws IllegalArgumentException If no matching enumeration value can be found
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*/
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public static RequestType fromString(String typeStr) {
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for (RequestType type : values()) {
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if (type.typeName.equalsIgnoreCase(typeStr)
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|| type.name().equalsIgnoreCase(typeStr)) {
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return type;
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}
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}
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throw new IllegalArgumentException("Invalid request type: " + typeStr);
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}
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}

‎src/main/java/chain/handler/ApprovalHandler.java‎

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package chain.handler;
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import chain.dto.ApprovalRequestDto;
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import chain.service.ApprovalRuleService;
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import java.util.List;
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public abstract class ApprovalHandler {
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protected ApprovalHandler next;
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private final List<ApprovalRuleService> rules;
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public ApprovalHandler(List<ApprovalRuleService> rules) {
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this.rules = rules;
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}
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//pipeline
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public ApprovalHandler linkWith(ApprovalHandler next) {
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this.next = next;
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return next;
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}
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public void handle(ApprovalRequestDto request) {
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if (rules.stream().anyMatch(rule -> rule.evaluate(request))) {
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System.out.printf("[%s]Approve the %s application for %s: days=%d, amount=%.2f%n",
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getClass().getSimpleName(), request.getApplicant(), request.getType(),
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request.getDays(), request.getAmount());
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} else {
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System.out.printf("[%s]Not in compliance with approval rules, transferred to the next level: %s%n",
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getClass().getSimpleName(), next != null ? next.getClass().getSimpleName() : "Null");
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passToNext(request);
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}
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}
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protected void passToNext(ApprovalRequestDto request) {
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if (next != null) {
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next.handle(request);
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} else {
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System.out.println("[SYSTEM] No one can process this request: " + request.getType());
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}
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}
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}

‎src/main/java/chain/processor/CEO.java‎

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package chain.processor;
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import chain.handler.ApprovalHandler;
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import chain.service.impl.DefaultRuleService;
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import java.util.List;
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public class CEO extends ApprovalHandler {
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public CEO() {
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super(List.of(new DefaultRuleService()));
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}
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}

‎src/main/java/chain/processor/DepartmentManager.java‎

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package chain.processor;
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import chain.handler.ApprovalHandler;
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import chain.service.impl.LeaveDaysRuleService;
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import java.util.List;
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public class DepartmentManager extends ApprovalHandler {
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public DepartmentManager() {
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super(List.of(new LeaveDaysRuleService(3)));
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}
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}

‎src/main/java/chain/processor/HRManager.java‎

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package chain.processor;
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import chain.handler.ApprovalHandler;
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import chain.service.impl.ExpenseAmountRuleService;
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import chain.service.impl.LeaveDaysRuleService;
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import java.util.Arrays;
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public class HRManager extends ApprovalHandler {
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public HRManager() {
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super(Arrays.asList(
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new LeaveDaysRuleService(7),
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new ExpenseAmountRuleService(1000)
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));
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}
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}

‎src/main/java/chain/service/ApprovalRuleService.java‎

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package chain.service;
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import chain.dto.ApprovalRequestDto;
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public interface ApprovalRuleService {
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boolean evaluate(ApprovalRequestDto request);
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String getName();
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}

‎src/main/java/chain/service/impl/DefaultRuleService.java‎

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package chain.service.impl;
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import chain.dto.ApprovalRequestDto;
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import chain.service.ApprovalRuleService;
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public class DefaultRuleService implements ApprovalRuleService {
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@Override
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public boolean evaluate(ApprovalRequestDto request) {
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return true;
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}
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@Override
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public String getName() {
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return "True";
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}
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}

‎src/main/java/chain/service/impl/ExpenseAmountRuleService.java‎

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package chain.service.impl;
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import chain.dto.ApprovalRequestDto;
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import chain.enums.RequestType;
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import chain.service.ApprovalRuleService;
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public class ExpenseAmountRuleService implements ApprovalRuleService {
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private final double maxAmount;
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public ExpenseAmountRuleService(double maxAmount) {
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this.maxAmount = maxAmount;
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}
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@Override
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public boolean evaluate(ApprovalRequestDto req) {
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return req.getType() == RequestType.EXPENSE && req.getAmount() <= maxAmount;
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}
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@Override
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public String getName() {
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return "Expense<=" + maxAmount;
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}
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}

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