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https://github.com/tiennm99/java-design-patterns.git
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BAGHDAD MohamedandGitHub
5d6ff2f0c4
Add an educational rule-engine module demonstrating the Rule Engine pattern. Each business rule is an independent object exposing evaluate (decision) and execute (action); a RuleEngine evaluates a collection of rules against an immutable loan-application context in insertion order, runs the passing rules, and reports every passed and failed rule via an immutable RuleEngineResult. Includes three concrete rules, an App demo, unit tests, README, and class diagram.
92 lines
3.6 KiB
Java
92 lines
3.6 KiB
Java
/*
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* This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
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*
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* The MIT License
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* Copyright © 2014-2022 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.ruleengine;
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import java.util.ArrayList;
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import java.util.List;
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import java.util.Objects;
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/**
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* Orchestrates a fixed collection of {@link Rule rules} against a context.
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*
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* <p>The engine owns the coordination logic that would otherwise live in a large nested {@code
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* if}/{@code else} block: it evaluates every rule in insertion order, runs the action of each rule
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* whose condition is satisfied, and reports the combined outcome as a {@link RuleEngineResult}.
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* Evaluation never stops early, so a single run reports <em>all</em> failing rules rather than only
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* the first, which is what makes rejection reasons useful.
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*
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* <p>The rule collection is copied defensively on construction, making the engine immutable and
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* safe to reuse across many contexts. New behaviour is added by supplying additional {@link Rule}
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* implementations; the engine itself never changes.
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*
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* @param <T> type of the context the rules are evaluated against
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*/
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public class RuleEngine<T> {
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private final List<Rule<T>> rules;
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/**
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* Creates an engine for the given rules.
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*
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* @param rules the rules to evaluate, applied in iteration order; must not be {@code null} or
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* contain {@code null} elements
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* @throws NullPointerException if {@code rules} is {@code null} or contains a {@code null} rule
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*/
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public RuleEngine(List<Rule<T>> rules) {
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this.rules = List.copyOf(rules);
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}
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/**
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* Evaluates every rule against the context and executes the rules that pass.
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*
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* @param context the context inspected by the rules; must not be {@code null}
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* @return the combined outcome of the run
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* @throws NullPointerException if {@code context} is {@code null}
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*/
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public RuleEngineResult run(T context) {
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Objects.requireNonNull(context, "context must not be null");
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List<String> passed = new ArrayList<>();
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List<String> failed = new ArrayList<>();
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for (Rule<T> rule : rules) {
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if (rule.evaluate(context)) {
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rule.execute(context);
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passed.add(rule.name());
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} else {
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failed.add(rule.name());
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}
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}
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return new RuleEngineResult(failed.isEmpty(), passed, failed);
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}
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/**
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* Returns the rules held by this engine.
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*
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* @return an immutable view of the configured rules
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*/
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public List<Rule<T>> rules() {
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return rules;
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}
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}
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