feat: Added Map Reduce Design Pattern (#3184)

* MapReduce design pattern added * Updated README.md * added module to parent pom
2026-05-22 04:25:35 +00:00 · 2025-02-22 13:08:05 -05:00
parent e17f138223
commit 6785b53b02
14 changed files with 815 additions and 0 deletions
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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).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package com.iluwatar;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.Map;
+import java.util.logging.Logger;
+
+/**
+ * The Main class serves as the entry point for executing the MapReduce program.
+ * It processes a list of text inputs, applies the MapReduce pattern, and prints the results.
+ */
+public class Main {
+  private static final Logger logger = Logger.getLogger(Main.class.getName());
+  /**
+   * The main method initiates the MapReduce process and displays the word count results.
+   *
+   * @param args Command-line arguments (not used).
+   */
+  public static void main(String[] args) {
+    List<String> inputs = Arrays.asList(
+        "Hello world hello",
+        "MapReduce is fun",
+        "Hello from the other side",
+        "Hello world"
+    );
+    List<Map.Entry<String, Integer>> result = MapReduce.mapReduce(inputs);
+    for (Map.Entry<String, Integer> entry : result) {
+      logger.info(entry.getKey() + ": " + entry.getValue());
+    }
+  }
+}
@@ -0,0 +1,55 @@
+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package com.iluwatar;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * The MapReduce class orchestrates the MapReduce process,
+ * calling the Mapper, Shuffler, and Reducer components.
+ */
+public class MapReduce {
+  private MapReduce() {
+    throw new UnsupportedOperationException("MapReduce is a utility class and cannot be instantiated.");
+  }
+  /**
+   * Executes the MapReduce process on the given list of input strings.
+   *
+   * @param inputs List of input strings to be processed.
+   * @return A list of word counts sorted in descending order.
+   */
+  public static List<Map.Entry<String, Integer>> mapReduce(List<String> inputs) {
+    List<Map<String, Integer>> mapped = new ArrayList<>();
+    for (String input : inputs) {
+      mapped.add(Mapper.map(input));
+    }
+
+    Map<String, List<Integer>> grouped = Shuffler.shuffleAndSort(mapped);
+
+    return Reducer.reduce(grouped);
+  }
+}
@@ -0,0 +1,56 @@
+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package com.iluwatar;
+
+import java.util.HashMap;
+import java.util.Map;
+
+
+/**
+ * The Mapper class is responsible for processing an input string
+ * and generating a map of word occurrences.
+ */
+public class Mapper {
+  private Mapper() {
+    throw new UnsupportedOperationException("Mapper is a utility class and cannot be instantiated.");
+  }
+  /**
+   * Splits a given input string into words and counts their occurrences.
+   *
+   * @param input The input string to be mapped.
+   * @return A map where keys are words and values are their respective counts.
+   */
+  public static Map<String, Integer> map(String input) {
+    Map<String, Integer> wordCount = new HashMap<>();
+    String[] words = input.split("\\s+");
+    for (String word : words) {
+      word = word.toLowerCase().replaceAll("[^a-z]", "");
+      if (!word.isEmpty()) {
+        wordCount.put(word, wordCount.getOrDefault(word, 0) + 1);
+      }
+    }
+    return wordCount;
+  }
+}
@@ -0,0 +1,56 @@
+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package com.iluwatar;
+
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * The Reducer class is responsible for aggregating word counts from the shuffled data.
+ */
+public class Reducer {
+  private Reducer() {
+    throw new UnsupportedOperationException("Reducer is a utility class and cannot be instantiated.");
+  }
+  /**
+   * Sums the occurrences of each word and sorts the results in descending order.
+   *
+   * @param grouped A map where keys are words and values are lists of their occurrences.
+   * @return A sorted list of word counts in descending order.
+   */
+  public static List<Map.Entry<String, Integer>> reduce(Map<String, List<Integer>> grouped) {
+    Map<String, Integer> reduced = new HashMap<>();
+    for (Map.Entry<String, List<Integer>> entry : grouped.entrySet()) {
+      reduced.put(entry.getKey(), entry.getValue().stream().mapToInt(Integer::intValue).sum());
+    }
+
+    List<Map.Entry<String, Integer>> result = new ArrayList<>(reduced.entrySet());
+    result.sort(Map.Entry.comparingByValue(Comparator.reverseOrder()));
+    return result;
+  }
+}
@@ -0,0 +1,56 @@
+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package com.iluwatar;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * The Shuffler class is responsible for grouping word occurrences from multiple mappers.
+ */
+public class Shuffler {
+
+  private Shuffler() {
+    throw new UnsupportedOperationException("Shuffler is a utility class and cannot be instantiated.");
+  }
+  /**
+   * Merges multiple word count maps into a single grouped map.
+   *
+   * @param mapped List of maps containing word counts from the mapping phase.
+   * @return A map where keys are words and values are lists of their occurrences across inputs.
+   */
+  public static Map<String, List<Integer>> shuffleAndSort(List<Map<String, Integer>> mapped) {
+    Map<String, List<Integer>> grouped = new HashMap<>();
+    for (Map<String, Integer> map : mapped) {
+      for (Map.Entry<String, Integer> entry : map.entrySet()) {
+        grouped.putIfAbsent(entry.getKey(), new ArrayList<>());
+        grouped.get(entry.getKey()).add(entry.getValue());
+      }
+    }
+    return grouped;
+  }
+}
@@ -0,0 +1,48 @@
+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package com.iluwatar;
+
+import org.junit.jupiter.api.Test;
+import java.util.*;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class MapReduceTest {
+
+  @Test
+  void testMapReduce() {
+    List<String> inputs = Arrays.asList(
+        "Hello world hello",
+        "MapReduce is fun",
+        "Hello from the other side"
+    );
+
+    List<Map.Entry<String, Integer>> result = MapReduce.mapReduce(inputs);
+
+    assertEquals("hello", result.get(0).getKey());  // hello = 3
+    assertEquals(3, result.get(0).getValue());
+    assertEquals(1, result.get(1).getValue());
+  }
+}
@@ -0,0 +1,50 @@
+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package com.iluwatar;
+
+import org.junit.jupiter.api.Test;
+import java.util.Map;
+import static org.junit.jupiter.api.Assertions.*;
+
+class MapperTest {
+
+  @Test
+  void testMapSingleSentence() {
+    String input = "Hello world hello";
+    Map<String, Integer> result = Mapper.map(input);
+
+    assertEquals(2, result.get("hello"));
+    assertEquals(1, result.get("world"));
+  }
+
+  @Test
+  void testMapCaseInsensitivity() {
+    String input = "HeLLo WoRLd hello WORLD";
+    Map<String, Integer> result = Mapper.map(input);
+
+    assertEquals(2, result.get("hello"));
+    assertEquals(2, result.get("world"));
+  }
+}
@@ -0,0 +1,74 @@
+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package com.iluwatar;
+
+import org.junit.jupiter.api.Test;
+import java.util.*;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class ReducerTest {
+
+  @Test
+  void testReduceWithMultipleWords() {
+    Map<String, List<Integer>> input = new HashMap<>();
+    input.put("apple", Arrays.asList(2, 3, 1));
+    input.put("banana", Arrays.asList(1, 1));
+    input.put("cherry", List.of(4));
+
+    List<Map.Entry<String, Integer>> result = Reducer.reduce(input);
+
+    assertEquals(3, result.size());
+    assertEquals("apple", result.get(0).getKey());
+    assertEquals(6, result.get(0).getValue());
+    assertEquals("cherry", result.get(1).getKey());
+    assertEquals(4, result.get(1).getValue());
+    assertEquals("banana", result.get(2).getKey());
+    assertEquals(2, result.get(2).getValue());
+  }
+
+  @Test
+  void testReduceWithEmptyInput() {
+    Map<String, List<Integer>> input = new HashMap<>();
+
+    List<Map.Entry<String, Integer>> result = Reducer.reduce(input);
+
+    assertTrue(result.isEmpty());
+  }
+
+  @Test
+  void testReduceWithTiedCounts() {
+    Map<String, List<Integer>> input = new HashMap<>();
+    input.put("tie1", Arrays.asList(2, 2));
+    input.put("tie2", Arrays.asList(1, 3));
+
+    List<Map.Entry<String, Integer>> result = Reducer.reduce(input);
+
+    assertEquals(2, result.size());
+    assertEquals(4, result.get(0).getValue());
+    assertEquals(4, result.get(1).getValue());
+    // Note: The order of tie1 and tie2 is not guaranteed in case of a tie
+  }
+}
@@ -0,0 +1,47 @@
+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package com.iluwatar;
+
+import org.junit.jupiter.api.Test;
+import java.util.*;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class ShufflerTest {
+
+  @Test
+  void testShuffleAndSort() {
+    List<Map<String, Integer>> mappedData = Arrays.asList(
+        Map.of("hello", 1, "world", 2),
+        Map.of("hello", 2, "java", 1)
+    );
+
+    Map<String, List<Integer>> grouped = Shuffler.shuffleAndSort(mappedData);
+
+    assertEquals(Arrays.asList(1, 2), grouped.get("hello"));
+    assertEquals(List.of(2), grouped.get("world"));
+    assertEquals(List.of(1), grouped.get("java"));
+  }
+}