From 520262bcd46fbf5d9d0a4c75bb3258028e993575 Mon Sep 17 00:00:00 2001
From: Amar Wadhwani <ds24m023@technikum-wien.at>
Date: Sun, 27 Apr 2025 20:43:43 +0200
Subject: [PATCH 1/3] BAEL-9210: Stream Gatherers

---
 core-java-modules/core-java-streams-7/pom.xml |  4 +-
 .../streams/gatherer/NumericSumGatherer.java  | 39 ++++++++++
 .../gatherer/SentenceSplitterGatherer.java    | 36 +++++++++
 .../gatherer/SlidingWindowGatherer.java       | 40 ++++++++++
 .../streams/gatherer/GathererUnitTest.java    | 62 +++++++++++++++
 .../gatherer/NumericSumGathererUnitTest.java  | 18 +++++
 .../SentenceSplitterGathererUnitTest.java     | 19 +++++
 .../SlidingWindowGathererUnitTest.java        | 21 +++++
 core-java-modules/pom.xml                     |  2 +-
 pom.xml                                       | 77 +++++++++++++++++++
 10 files changed, 315 insertions(+), 3 deletions(-)
 create mode 100644 core-java-modules/core-java-streams-7/src/main/java/com/baeldung/streams/gatherer/NumericSumGatherer.java
 create mode 100644 core-java-modules/core-java-streams-7/src/main/java/com/baeldung/streams/gatherer/SentenceSplitterGatherer.java
 create mode 100644 core-java-modules/core-java-streams-7/src/main/java/com/baeldung/streams/gatherer/SlidingWindowGatherer.java
 create mode 100644 core-java-modules/core-java-streams-7/src/test/java/com/baeldung/streams/gatherer/GathererUnitTest.java
 create mode 100644 core-java-modules/core-java-streams-7/src/test/java/com/baeldung/streams/gatherer/NumericSumGathererUnitTest.java
 create mode 100644 core-java-modules/core-java-streams-7/src/test/java/com/baeldung/streams/gatherer/SentenceSplitterGathererUnitTest.java
 create mode 100644 core-java-modules/core-java-streams-7/src/test/java/com/baeldung/streams/gatherer/SlidingWindowGathererUnitTest.java

diff --git a/core-java-modules/core-java-streams-7/pom.xml b/core-java-modules/core-java-streams-7/pom.xml
index 892ad66f94f4..39cb2e46aa0b 100644
--- a/core-java-modules/core-java-streams-7/pom.xml
+++ b/core-java-modules/core-java-streams-7/pom.xml
@@ -35,8 +35,8 @@
     </build>
 
     <properties>
-        <maven.compiler.source>12</maven.compiler.source>
-        <maven.compiler.target>12</maven.compiler.target>
+        <maven.compiler.source>24</maven.compiler.source>
+        <maven.compiler.target>24</maven.compiler.target>
         <vavr.version>0.10.2</vavr.version>
         <assertj-core.version>3.23.1</assertj-core.version>
         <commons-lang3.version>3.12.0</commons-lang3.version>
diff --git a/core-java-modules/core-java-streams-7/src/main/java/com/baeldung/streams/gatherer/NumericSumGatherer.java b/core-java-modules/core-java-streams-7/src/main/java/com/baeldung/streams/gatherer/NumericSumGatherer.java
new file mode 100644
index 000000000000..62ac79880f94
--- /dev/null
+++ b/core-java-modules/core-java-streams-7/src/main/java/com/baeldung/streams/gatherer/NumericSumGatherer.java
@@ -0,0 +1,39 @@
+package com.baeldung.streams.gatherer;
+
+import java.util.ArrayList;
+import java.util.function.BiConsumer;
+import java.util.function.Supplier;
+import java.util.stream.Gatherer;
+
+public class NumericSumGatherer implements Gatherer<Integer, ArrayList<Integer>, Integer> {
+
+    @Override
+    public Supplier<ArrayList<Integer>> initializer() {
+        return ArrayList::new;
+    }
+
+    @Override
+    public Integrator<ArrayList<Integer>, Integer, Integer> integrator() {
+        return new Integrator<>() {
+            @Override
+            public boolean integrate(ArrayList<Integer> state, Integer element, Downstream<? super Integer> downstream) {
+                if (state.isEmpty()) {
+                    state.add(element);
+                } else {
+                    state.addFirst(state.getFirst() + element);
+                }
+                return true;
+            }
+        };
+    }
+
+    @Override
+    public BiConsumer<ArrayList<Integer>, Downstream<? super Integer>> finisher() {
+        return (state, downstream) -> {
+            if (!downstream.isRejecting() && !state.isEmpty()) {
+                downstream.push(state.getFirst());
+                state.clear();
+            }
+        };
+    }
+}
diff --git a/core-java-modules/core-java-streams-7/src/main/java/com/baeldung/streams/gatherer/SentenceSplitterGatherer.java b/core-java-modules/core-java-streams-7/src/main/java/com/baeldung/streams/gatherer/SentenceSplitterGatherer.java
new file mode 100644
index 000000000000..af3b2f7acd74
--- /dev/null
+++ b/core-java-modules/core-java-streams-7/src/main/java/com/baeldung/streams/gatherer/SentenceSplitterGatherer.java
@@ -0,0 +1,36 @@
+package com.baeldung.streams.gatherer;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.function.BinaryOperator;
+import java.util.function.Supplier;
+import java.util.stream.Gatherer;
+
+public class SentenceSplitterGatherer implements Gatherer<String, List<String>,String> {
+
+    @Override
+    public Supplier<List<String>> initializer() {
+        return ArrayList::new;
+    }
+
+    @Override
+    public BinaryOperator<List<String>> combiner() {
+        return (left, right) -> {
+            left.addAll(right);
+            return left;
+        };
+    }
+
+    @Override
+    public Integrator<List<String>, String, String> integrator() {
+        return (state, element, downstream) -> {
+            var words = element.split("\\s+");
+            for (var word : words) {
+                state.add(word);
+                downstream.push(word);
+            }
+            return true;
+        };
+    }
+}
diff --git a/core-java-modules/core-java-streams-7/src/main/java/com/baeldung/streams/gatherer/SlidingWindowGatherer.java b/core-java-modules/core-java-streams-7/src/main/java/com/baeldung/streams/gatherer/SlidingWindowGatherer.java
new file mode 100644
index 000000000000..4b85ab58663b
--- /dev/null
+++ b/core-java-modules/core-java-streams-7/src/main/java/com/baeldung/streams/gatherer/SlidingWindowGatherer.java
@@ -0,0 +1,40 @@
+package com.baeldung.streams.gatherer;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.function.BiConsumer;
+import java.util.function.Supplier;
+import java.util.stream.Gatherer;
+
+public class SlidingWindowGatherer implements Gatherer<Integer, ArrayList<Integer>, List<Integer>> {
+
+    @Override
+    public Supplier<ArrayList<Integer>> initializer() {
+        return ArrayList::new;
+    }
+
+    @Override
+    public Integrator<ArrayList<Integer>, Integer, List<Integer>> integrator() {
+        return new Integrator<>() {
+            @Override
+            public boolean integrate(ArrayList<Integer> state, Integer element, Downstream<? super List<Integer>> downstream) {
+                state.add(element);
+                if (state.size() == 3) {
+                    downstream.push(new ArrayList<>(state));
+                    state.removeFirst();
+                }
+                return true;
+            }
+        };
+    }
+
+    @Override
+    public BiConsumer<ArrayList<Integer>, Downstream<? super List<Integer>>> finisher() {
+        return (state, downstream) -> {
+            if (state.size()==3) {
+                downstream.push(new ArrayList<>(state));
+            }
+        };
+
+    }
+}
diff --git a/core-java-modules/core-java-streams-7/src/test/java/com/baeldung/streams/gatherer/GathererUnitTest.java b/core-java-modules/core-java-streams-7/src/test/java/com/baeldung/streams/gatherer/GathererUnitTest.java
new file mode 100644
index 000000000000..5373745dea96
--- /dev/null
+++ b/core-java-modules/core-java-streams-7/src/test/java/com/baeldung/streams/gatherer/GathererUnitTest.java
@@ -0,0 +1,62 @@
+package com.baeldung.streams.gatherer;
+
+import java.util.List;
+import java.util.stream.Gatherer;
+import java.util.stream.Gatherers;
+import java.util.stream.Stream;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+class GathererUnitTest {
+
+    @Test
+    void givenNumbers_whenFolded_thenSumIsEmitted() {
+        Stream<Integer> numbers = Stream.of(1, 2, 3, 4, 5);
+        Stream<Integer> folded = numbers.gather(Gatherers.fold(() -> 0, Integer::sum));
+        List<Integer> resultList = folded.toList();
+        Assertions.assertEquals(1, resultList.size());
+        Assertions.assertEquals(Integer.valueOf(15), resultList.getFirst());
+    }
+
+    @Test
+    void givenWords_whenMappedConcurrently_thenUppercasedWordsAreEmitted() {
+        Stream<String> words = Stream.of("a", "b", "c", "d");
+        List<String> resultList = words.gather(Gatherers.mapConcurrent(2, String::toUpperCase))
+            .toList();
+        Assertions.assertEquals(4, resultList.size());
+        Assertions.assertEquals(List.of("A", "B", "C", "D"), resultList);
+    }
+
+    @Test
+    void givenNumbers_whenScanned_thenRunningTotalsAreEmitted() {
+        Stream<Integer> numbers = Stream.of(1, 2, 3, 4);
+        List<Integer> resultList = numbers.gather(Gatherers.scan(() -> 0, Integer::sum))
+            .toList();
+        Assertions.assertEquals(4, resultList.size());
+        Assertions.assertEquals(List.of(1, 3, 6, 10), resultList);
+    }
+
+    @Test
+    void givenNumbers_whenWindowedSliding_thenOverlappingWindowsAreEmitted() {
+        List<List<Integer>> expectedOutput = List.of(List.of(1, 2, 3), List.of(2, 3, 4), List.of(3, 4, 5));
+        Stream<Integer> numbers = Stream.of(1, 2, 3, 4, 5);
+        List<List<Integer>> resultList = numbers.gather(Gatherers.windowSliding(3))
+            .toList();
+        Assertions.assertEquals(3, resultList.size());
+        Assertions.assertEquals(expectedOutput, resultList);
+    }
+
+    @Test
+    void givenStrings_whenUsingCustomGatherer_thenLengthsAreCalculated() {
+        List<Integer> expectedOutput = List.of(5, 6, 3);
+        Stream<String> inputStrings = Stream.of("apple", "banana", "cat");
+        List<Object> resultList = inputStrings.gather(Gatherer.of((state, element, downstream) -> {
+                downstream.push(element.length());
+                return true;
+            }))
+            .toList();
+        Assertions.assertEquals(3, resultList.size());
+        Assertions.assertEquals(expectedOutput, resultList);
+    }
+}
diff --git a/core-java-modules/core-java-streams-7/src/test/java/com/baeldung/streams/gatherer/NumericSumGathererUnitTest.java b/core-java-modules/core-java-streams-7/src/test/java/com/baeldung/streams/gatherer/NumericSumGathererUnitTest.java
new file mode 100644
index 000000000000..df16bf8f05f5
--- /dev/null
+++ b/core-java-modules/core-java-streams-7/src/test/java/com/baeldung/streams/gatherer/NumericSumGathererUnitTest.java
@@ -0,0 +1,18 @@
+package com.baeldung.streams.gatherer;
+
+import java.util.List;
+import java.util.stream.Stream;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+class NumericSumGathererUnitTest {
+
+    @Test
+    void givenNumbers_whenUsingCustomManyToOneGatherer_thenSumIsCalculated() {
+        Stream<Integer> inputValues = Stream.of(1, 2, 3, 4, 5, 6);
+        List<Integer> result = inputValues.gather(new NumericSumGatherer())
+            .toList();
+        Assertions.assertEquals(Integer.valueOf(21), result.getFirst());
+    }
+}
\ No newline at end of file
diff --git a/core-java-modules/core-java-streams-7/src/test/java/com/baeldung/streams/gatherer/SentenceSplitterGathererUnitTest.java b/core-java-modules/core-java-streams-7/src/test/java/com/baeldung/streams/gatherer/SentenceSplitterGathererUnitTest.java
new file mode 100644
index 000000000000..8a1b9eb4bf7e
--- /dev/null
+++ b/core-java-modules/core-java-streams-7/src/test/java/com/baeldung/streams/gatherer/SentenceSplitterGathererUnitTest.java
@@ -0,0 +1,19 @@
+package com.baeldung.streams.gatherer;
+
+import java.util.List;
+import java.util.stream.Stream;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+class SentenceSplitterGathererUnitTest {
+
+    @Test
+    void givenSentences_whenUsingCustomOneToManyGatherer_thenWordsAreExtracted() {
+        List<String> expectedOutput = List.of("hello", "world", "java", "streams");
+        Stream<String> sentences = Stream.of("hello world", "java streams");
+        List<String> words = sentences.gather(new SentenceSplitterGatherer())
+            .toList();
+        Assertions.assertEquals(expectedOutput, words);
+    }
+}
diff --git a/core-java-modules/core-java-streams-7/src/test/java/com/baeldung/streams/gatherer/SlidingWindowGathererUnitTest.java b/core-java-modules/core-java-streams-7/src/test/java/com/baeldung/streams/gatherer/SlidingWindowGathererUnitTest.java
new file mode 100644
index 000000000000..99e6f02018e0
--- /dev/null
+++ b/core-java-modules/core-java-streams-7/src/test/java/com/baeldung/streams/gatherer/SlidingWindowGathererUnitTest.java
@@ -0,0 +1,21 @@
+package com.baeldung.streams.gatherer;
+
+import java.util.List;
+import java.util.stream.Stream;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+class SlidingWindowGathererUnitTest {
+
+    @Test
+    void givenNumbers_whenWindowedSliding_thenOverlappingWindowsAreEmitted() {
+        List<List<Integer>> expectedOutput = List.of(List.of(1, 2, 3), List.of(2, 3, 4), List.of(3, 4, 5));
+        Stream<Integer> numbers = Stream.of(1, 2, 3, 4, 5);
+        List<List<Integer>> resultList = numbers.gather(new SlidingWindowGatherer())
+            .toList();
+        Assertions.assertEquals(3, resultList.size());
+        Assertions.assertEquals(expectedOutput, resultList);
+    }
+
+}
\ No newline at end of file
diff --git a/core-java-modules/pom.xml b/core-java-modules/pom.xml
index 93c923a683eb..66fd2c39031e 100644
--- a/core-java-modules/pom.xml
+++ b/core-java-modules/pom.xml
@@ -61,7 +61,7 @@
         <module>core-java-streams-4</module>
         <module>core-java-streams-5</module>
         <module>core-java-streams-6</module>
-        <module>core-java-streams-7</module>
+        <!-- <module>core-java-streams-7</module> requires JDK 24-->
         <module>core-java-streams-collect</module>
         <module>core-java-streams-maps</module>
         <module>core-java-string-operations-3</module>
diff --git a/pom.xml b/pom.xml
index 73621491ce6d..780b2396ed31 100644
--- a/pom.xml
+++ b/pom.xml
@@ -921,6 +921,47 @@
 
         </profile>
 
+        <profile>
+            <id>default-jdk24</id>
+            <build>
+                <plugins>
+                    <plugin>
+                        <groupId>org.apache.maven.plugins</groupId>
+                        <artifactId>maven-surefire-plugin</artifactId>
+                        <configuration>
+                            <forkCount>3</forkCount>
+                            <reuseForks>true</reuseForks>
+                            <includes>
+                                <include>SpringContextTest</include>
+                                <include>**/*UnitTest</include>
+                            </includes>
+                            <excludes>
+                                <exclude>**/*IntegrationTest.java</exclude>
+                                <exclude>**/*IntTest.java</exclude>
+                                <exclude>**/*LongRunningUnitTest.java</exclude>
+                                <exclude>**/*ManualTest.java</exclude>
+                                <exclude>**/JdbcTest.java</exclude>
+                                <exclude>**/*LiveTest.java</exclude>
+                            </excludes>
+                        </configuration>
+                    </plugin>
+                </plugins>
+            </build>
+
+            <modules>
+                <module>core-java-modules/core-java-streams-7</module>
+            </modules>
+
+            <properties>
+                <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+                <java.version>24</java.version>
+                <maven.compiler.source>24</maven.compiler.source>
+                <maven.compiler.target>24</maven.compiler.target>
+                <maven-pmd-plugin.version>3.26.0</maven-pmd-plugin.version>
+            </properties>
+
+        </profile>
+
         <profile>
             <id>integration-jdk17</id>
             <build>
@@ -1299,6 +1340,42 @@
 
         </profile>
 
+        <profile>
+            <id>integration-jdk24</id>
+            <build>
+                <plugins>
+                    <plugin>
+                        <groupId>org.apache.maven.plugins</groupId>
+                        <artifactId>maven-surefire-plugin</artifactId>
+                        <version>${maven-surefire-plugin.version}</version>
+                        <configuration>
+                            <excludes>
+                                <exclude>**/*ManualTest.java</exclude>
+                                <exclude>**/*LiveTest.java</exclude>
+                            </excludes>
+                            <includes>
+                                <include>**/*IntegrationTest.java</include>
+                                <include>**/*IntTest.java</include>
+                            </includes>
+                        </configuration>
+                    </plugin>
+                </plugins>
+            </build>
+
+            <modules>
+                <module>core-java-modules/core-java-streams-7</module>
+            </modules>
+
+            <properties>
+                <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+                <java.version>24</java.version>
+                <maven.compiler.source>24</maven.compiler.source>
+                <maven.compiler.target>24</maven.compiler.target>
+                <maven-pmd-plugin.version>3.26.0</maven-pmd-plugin.version>
+            </properties>
+
+        </profile>
+
         <profile>
             <id>live-all</id>
             <build>

From fc9bf77eec8b86e9747d40576a0987d9da66c646 Mon Sep 17 00:00:00 2001
From: Amar Wadhwani <ds24m023@technikum-wien.at>
Date: Sat, 9 Aug 2025 13:46:01 +0530
Subject: [PATCH 2/3] BAEL-9162: Simple Rule Engine

---
 rule-engines-modules/pom.xml                  |  1 +
 .../simple-rule-engine/pom.xml                | 43 +++++++++++++++++++
 ...irstOrderHighValueSpecialDiscountRule.java | 17 ++++++++
 .../java/com/baeldung/ruleengine/IRule.java   |  8 ++++
 .../ruleengine/LoyaltyDiscountRule.java       | 16 +++++++
 .../com/baeldung/ruleengine/RuleEngine.java   | 21 +++++++++
 .../com/baeldung/ruleengine/SpelRule.java     | 31 +++++++++++++
 .../baeldung/ruleengine/model/Customer.java   | 26 +++++++++++
 .../com/baeldung/ruleengine/model/Order.java  | 25 +++++++++++
 .../src/main/resources/logback.xml            | 13 ++++++
 .../ruleengine/RuleEngineUnitTest.java        | 40 +++++++++++++++++
 .../baeldung/ruleengine/SpelRuleUnitTest.java | 34 +++++++++++++++
 .../src/test/resources/logback.xml            | 13 ++++++
 13 files changed, 288 insertions(+)
 create mode 100644 rule-engines-modules/simple-rule-engine/pom.xml
 create mode 100644 rule-engines-modules/simple-rule-engine/src/main/java/com/baeldung/ruleengine/FirstOrderHighValueSpecialDiscountRule.java
 create mode 100644 rule-engines-modules/simple-rule-engine/src/main/java/com/baeldung/ruleengine/IRule.java
 create mode 100644 rule-engines-modules/simple-rule-engine/src/main/java/com/baeldung/ruleengine/LoyaltyDiscountRule.java
 create mode 100644 rule-engines-modules/simple-rule-engine/src/main/java/com/baeldung/ruleengine/RuleEngine.java
 create mode 100644 rule-engines-modules/simple-rule-engine/src/main/java/com/baeldung/ruleengine/SpelRule.java
 create mode 100644 rule-engines-modules/simple-rule-engine/src/main/java/com/baeldung/ruleengine/model/Customer.java
 create mode 100644 rule-engines-modules/simple-rule-engine/src/main/java/com/baeldung/ruleengine/model/Order.java
 create mode 100644 rule-engines-modules/simple-rule-engine/src/main/resources/logback.xml
 create mode 100644 rule-engines-modules/simple-rule-engine/src/test/java/com/baeldung/ruleengine/RuleEngineUnitTest.java
 create mode 100644 rule-engines-modules/simple-rule-engine/src/test/java/com/baeldung/ruleengine/SpelRuleUnitTest.java
 create mode 100644 rule-engines-modules/simple-rule-engine/src/test/resources/logback.xml

diff --git a/rule-engines-modules/pom.xml b/rule-engines-modules/pom.xml
index dcd97c5f275a..bc163f8034a6 100644
--- a/rule-engines-modules/pom.xml
+++ b/rule-engines-modules/pom.xml
@@ -18,6 +18,7 @@
         <module>evrete</module>
         <module>openl-tablets</module>
         <module>rulebook</module>
+        <module>simple-rule-engine</module>
         <!-- <module>jess</module> --> <!-- requires dependencies which are not publicly available -->
     </modules>
 
diff --git a/rule-engines-modules/simple-rule-engine/pom.xml b/rule-engines-modules/simple-rule-engine/pom.xml
new file mode 100644
index 000000000000..0ff8b0427e66
--- /dev/null
+++ b/rule-engines-modules/simple-rule-engine/pom.xml
@@ -0,0 +1,43 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <groupId>com.baeldung.simpleruleengine</groupId>
+    <artifactId>simple-rule-engine</artifactId>
+    <version>1.0</version>
+    <name>simple-rule-engine</name>
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <configuration>
+                    <source>9</source>
+                    <target>9</target>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>rule-engines-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.projectlombok</groupId>
+            <artifactId>lombok</artifactId>
+            <version>${lombok.version}</version>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework</groupId>
+            <artifactId>spring-expression</artifactId>
+            <version>7.0.0-M7</version>
+        </dependency>
+    </dependencies>
+
+</project>
\ No newline at end of file
diff --git a/rule-engines-modules/simple-rule-engine/src/main/java/com/baeldung/ruleengine/FirstOrderHighValueSpecialDiscountRule.java b/rule-engines-modules/simple-rule-engine/src/main/java/com/baeldung/ruleengine/FirstOrderHighValueSpecialDiscountRule.java
new file mode 100644
index 000000000000..514cc74ad4cd
--- /dev/null
+++ b/rule-engines-modules/simple-rule-engine/src/main/java/com/baeldung/ruleengine/FirstOrderHighValueSpecialDiscountRule.java
@@ -0,0 +1,17 @@
+package com.baeldung.ruleengine;
+
+import com.baeldung.ruleengine.model.Order;
+
+public class FirstOrderHighValueSpecialDiscountRule implements IRule {
+
+    @Override
+    public boolean evaluate(Order order) {
+        return order.getCustomer()
+            .isFirstOrder() && order.getAmount() > 500;
+    }
+
+    @Override
+    public String description() {
+        return "First Order Special Discount Rule: First Time customer with high value order";
+    }
+}
diff --git a/rule-engines-modules/simple-rule-engine/src/main/java/com/baeldung/ruleengine/IRule.java b/rule-engines-modules/simple-rule-engine/src/main/java/com/baeldung/ruleengine/IRule.java
new file mode 100644
index 000000000000..1f79f49fdd4b
--- /dev/null
+++ b/rule-engines-modules/simple-rule-engine/src/main/java/com/baeldung/ruleengine/IRule.java
@@ -0,0 +1,8 @@
+package com.baeldung.ruleengine;
+
+import com.baeldung.ruleengine.model.Order;
+
+public interface IRule {
+    boolean evaluate(Order order);
+    String description();
+}
diff --git a/rule-engines-modules/simple-rule-engine/src/main/java/com/baeldung/ruleengine/LoyaltyDiscountRule.java b/rule-engines-modules/simple-rule-engine/src/main/java/com/baeldung/ruleengine/LoyaltyDiscountRule.java
new file mode 100644
index 000000000000..86bd39fab28a
--- /dev/null
+++ b/rule-engines-modules/simple-rule-engine/src/main/java/com/baeldung/ruleengine/LoyaltyDiscountRule.java
@@ -0,0 +1,16 @@
+package com.baeldung.ruleengine;
+
+import com.baeldung.ruleengine.model.Order;
+
+public class LoyaltyDiscountRule implements IRule{
+
+    @Override
+    public boolean evaluate(Order order) {
+        return order.getCustomer().getLoyaltyPoints() > 500;
+    }
+
+    @Override
+    public String description() {
+        return "Loyalty Discount Rule: Customer has more than 500 points";
+    }
+}
diff --git a/rule-engines-modules/simple-rule-engine/src/main/java/com/baeldung/ruleengine/RuleEngine.java b/rule-engines-modules/simple-rule-engine/src/main/java/com/baeldung/ruleengine/RuleEngine.java
new file mode 100644
index 000000000000..cc199cfa85da
--- /dev/null
+++ b/rule-engines-modules/simple-rule-engine/src/main/java/com/baeldung/ruleengine/RuleEngine.java
@@ -0,0 +1,21 @@
+package com.baeldung.ruleengine;
+
+import java.util.List;
+import java.util.stream.Collectors;
+
+import com.baeldung.ruleengine.model.Order;
+
+public class RuleEngine {
+    private final List<IRule> rules;
+
+    public RuleEngine(List<IRule> rules) {
+        this.rules = rules;
+    }
+
+    public List<String> evaluate(Order order) {
+        return rules.stream()
+            .filter(rule -> rule.evaluate(order))
+            .map(IRule::description)
+            .collect(Collectors.toList());
+    }
+}
diff --git a/rule-engines-modules/simple-rule-engine/src/main/java/com/baeldung/ruleengine/SpelRule.java b/rule-engines-modules/simple-rule-engine/src/main/java/com/baeldung/ruleengine/SpelRule.java
new file mode 100644
index 000000000000..9a386bf9f2f4
--- /dev/null
+++ b/rule-engines-modules/simple-rule-engine/src/main/java/com/baeldung/ruleengine/SpelRule.java
@@ -0,0 +1,31 @@
+package com.baeldung.ruleengine;
+
+import org.springframework.expression.ExpressionParser;
+import org.springframework.expression.spel.standard.SpelExpressionParser;
+import org.springframework.expression.spel.support.StandardEvaluationContext;
+
+import com.baeldung.ruleengine.model.Order;
+
+
+public class SpelRule {
+
+    private final String expression;
+    private final String description;
+
+    public SpelRule(String expression, String description) {
+        this.expression = expression;
+        this.description = description;
+    }
+
+    public boolean evaluate(Order order) {
+        ExpressionParser parser = new SpelExpressionParser();
+        StandardEvaluationContext context = new StandardEvaluationContext(order);
+        context.setVariable("order", order);
+        return parser.parseExpression(expression)
+            .getValue(context, Boolean.class);
+    }
+
+    public String getDescription() {
+        return description;
+    }
+}
diff --git a/rule-engines-modules/simple-rule-engine/src/main/java/com/baeldung/ruleengine/model/Customer.java b/rule-engines-modules/simple-rule-engine/src/main/java/com/baeldung/ruleengine/model/Customer.java
new file mode 100644
index 000000000000..8264a6afaf4e
--- /dev/null
+++ b/rule-engines-modules/simple-rule-engine/src/main/java/com/baeldung/ruleengine/model/Customer.java
@@ -0,0 +1,26 @@
+package com.baeldung.ruleengine.model;
+
+import lombok.AccessLevel;
+import lombok.Getter;
+import lombok.Setter;
+import lombok.experimental.FieldDefaults;
+
+@Setter
+@Getter
+@FieldDefaults(level = AccessLevel.PRIVATE)
+public class Customer {
+
+    String name;
+    int loyaltyPoints;
+    boolean firstOrder;
+
+    public Customer() {
+    }
+
+    public Customer(String name, int loyaltyPoints, boolean firstOrder) {
+        this.name = name;
+        this.loyaltyPoints = loyaltyPoints;
+        this.firstOrder = firstOrder;
+    }
+
+}
diff --git a/rule-engines-modules/simple-rule-engine/src/main/java/com/baeldung/ruleengine/model/Order.java b/rule-engines-modules/simple-rule-engine/src/main/java/com/baeldung/ruleengine/model/Order.java
new file mode 100644
index 000000000000..4f9d0c7979f7
--- /dev/null
+++ b/rule-engines-modules/simple-rule-engine/src/main/java/com/baeldung/ruleengine/model/Order.java
@@ -0,0 +1,25 @@
+package com.baeldung.ruleengine.model;
+
+import lombok.AccessLevel;
+import lombok.AllArgsConstructor;
+import lombok.Data;
+import lombok.Getter;
+import lombok.NoArgsConstructor;
+import lombok.Setter;
+import lombok.experimental.FieldDefaults;
+
+@Getter
+@Setter
+public class Order {
+
+    private Double amount;
+    private Customer customer;
+
+    public Order() {
+    }
+
+    public Order(Double amount, Customer customer) {
+        this.amount = amount;
+        this.customer = customer;
+    }
+}
diff --git a/rule-engines-modules/simple-rule-engine/src/main/resources/logback.xml b/rule-engines-modules/simple-rule-engine/src/main/resources/logback.xml
new file mode 100644
index 000000000000..7d900d8ea884
--- /dev/null
+++ b/rule-engines-modules/simple-rule-engine/src/main/resources/logback.xml
@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<configuration>
+    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
+        <encoder>
+            <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n
+            </pattern>
+        </encoder>
+    </appender>
+
+    <root level="INFO">
+        <appender-ref ref="STDOUT" />
+    </root>
+</configuration>
\ No newline at end of file
diff --git a/rule-engines-modules/simple-rule-engine/src/test/java/com/baeldung/ruleengine/RuleEngineUnitTest.java b/rule-engines-modules/simple-rule-engine/src/test/java/com/baeldung/ruleengine/RuleEngineUnitTest.java
new file mode 100644
index 000000000000..c6f792e01776
--- /dev/null
+++ b/rule-engines-modules/simple-rule-engine/src/test/java/com/baeldung/ruleengine/RuleEngineUnitTest.java
@@ -0,0 +1,40 @@
+package com.baeldung.ruleengine;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.List;
+
+import com.baeldung.ruleengine.model.Customer;
+import com.baeldung.ruleengine.model.Order;
+
+public class RuleEngineUnitTest {
+
+    @Test
+    void whenTwoRulesTriggered_thenBothDescriptionsReturned() {
+        Customer customer = new Customer("Max", 550, true);
+        Order order = new Order(600.0, customer);
+
+        RuleEngine engine = new RuleEngine(List.of(new LoyaltyDiscountRule(), new FirstOrderHighValueSpecialDiscountRule()));
+
+        List<String> results = engine.evaluate(order);
+
+        assertEquals(2, results.size());
+        assertTrue(results.contains("Loyalty Discount Rule: Customer has more than 500 points"));
+        assertTrue(results.contains("First Order Special Discount Rule: First Time customer with high value order"));
+    }
+
+    @Test
+    void whenNoRulesTriggered_thenEmptyListReturned() {
+        Customer customer = new Customer("Max", 50, false);
+        Order order = new Order(200.0, customer);
+
+        RuleEngine engine = new RuleEngine(List.of(new LoyaltyDiscountRule(), new FirstOrderHighValueSpecialDiscountRule()));
+
+        List<String> results = engine.evaluate(order);
+
+        assertTrue(results.isEmpty());
+    }
+}
diff --git a/rule-engines-modules/simple-rule-engine/src/test/java/com/baeldung/ruleengine/SpelRuleUnitTest.java b/rule-engines-modules/simple-rule-engine/src/test/java/com/baeldung/ruleengine/SpelRuleUnitTest.java
new file mode 100644
index 000000000000..3d4a2c131027
--- /dev/null
+++ b/rule-engines-modules/simple-rule-engine/src/test/java/com/baeldung/ruleengine/SpelRuleUnitTest.java
@@ -0,0 +1,34 @@
+package com.baeldung.ruleengine;
+
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import com.baeldung.ruleengine.model.Customer;
+import com.baeldung.ruleengine.model.Order;
+
+public class SpelRuleUnitTest {
+
+    @Test
+    void whenLoyalCustomer_thenEligibleForDiscount() {
+        Customer customer = new Customer("Bob", 730, false);
+        Order order = new Order(200.0, customer);
+
+        SpelRule rule = new SpelRule(
+            "#order.customer.loyaltyPoints > 500",
+            "Loyalty discount rule"
+        );
+        assertTrue(rule.evaluate(order));
+    }
+
+    @Test
+    void whenFirstOrderHighAmount_thenEligibleForSpecialDiscount() {
+        Customer customer = new Customer("Bob", 0, true);
+        Order order = new Order(800.0, customer);
+
+        SpelRule approvalRule = new SpelRule(
+            "#order.customer.firstOrder and #order.amount > 500",
+            "First-time customer with high order gets special discount"
+        );
+        assertTrue(approvalRule.evaluate(order));
+    }
+}
diff --git a/rule-engines-modules/simple-rule-engine/src/test/resources/logback.xml b/rule-engines-modules/simple-rule-engine/src/test/resources/logback.xml
new file mode 100644
index 000000000000..7d900d8ea884
--- /dev/null
+++ b/rule-engines-modules/simple-rule-engine/src/test/resources/logback.xml
@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<configuration>
+    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
+        <encoder>
+            <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n
+            </pattern>
+        </encoder>
+    </appender>
+
+    <root level="INFO">
+        <appender-ref ref="STDOUT" />
+    </root>
+</configuration>
\ No newline at end of file

From 07b4b731a06dc1342b91e7cf0e6777877fb8f051 Mon Sep 17 00:00:00 2001
From: Amar Wadhwani <ds24m023@technikum-wien.at>
Date: Fri, 22 Aug 2025 22:50:17 +0530
Subject: [PATCH 3/3] BAEL-9162: Simple Rule Engine

---
 .../simple-rule-engine/pom.xml                 | 18 +++++-------------
 1 file changed, 5 insertions(+), 13 deletions(-)

diff --git a/rule-engines-modules/simple-rule-engine/pom.xml b/rule-engines-modules/simple-rule-engine/pom.xml
index 0ff8b0427e66..4911464dfe7a 100644
--- a/rule-engines-modules/simple-rule-engine/pom.xml
+++ b/rule-engines-modules/simple-rule-engine/pom.xml
@@ -7,18 +7,6 @@
     <artifactId>simple-rule-engine</artifactId>
     <version>1.0</version>
     <name>simple-rule-engine</name>
-    <build>
-        <plugins>
-            <plugin>
-                <groupId>org.apache.maven.plugins</groupId>
-                <artifactId>maven-compiler-plugin</artifactId>
-                <configuration>
-                    <source>9</source>
-                    <target>9</target>
-                </configuration>
-            </plugin>
-        </plugins>
-    </build>
 
     <parent>
         <groupId>com.baeldung</groupId>
@@ -36,8 +24,12 @@
         <dependency>
             <groupId>org.springframework</groupId>
             <artifactId>spring-expression</artifactId>
-            <version>7.0.0-M7</version>
+            <version>${spring-expression.version}</version>
         </dependency>
     </dependencies>
 
+    <properties>
+        <spring-expression.version>7.0.0-M7</spring-expression.version>
+    </properties>
+
 </project>
\ No newline at end of file