BAEL-2018

core-java-8/src/main/java/com/baeldung/convertlisttomap/Animal.java

@@ -0,0 +1,27 @@
+package com.baeldung.convertlisttomap;
+
+public class Animal {
+    private int id;
+    private String name;
+
+    public Animal(int id, String name) {
+        this.id = id;
+        this.setName(name);
+    }
+
+    public int getId() {
+        return id;
+    }
+
+    public void setId(int id) {
+        this.id = id;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+}

core-java-8/src/main/java/com/baeldung/convertlisttomap/ConvertListToMapService.java

@@ -0,0 +1,52 @@
+package com.baeldung.convertlisttomap;
+
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+import org.apache.commons.collections4.IterableUtils;
+import org.apache.commons.collections4.MapUtils;
+import com.google.common.collect.Maps;
+
+public class ConvertListToMapService {
+
+    public Map<Integer, Animal> convertListBeforeJava8(List<Animal> list) {
+        Map<Integer, Animal> map = new HashMap<Integer, Animal>();
+        for (Animal animal : list) {
+            map.put(animal.getId(), animal);
+        }
+        return map;
+    }
+
+    public Map<Integer, Animal> convertListAfterJava8(List<Animal> list) {
+        Map<Integer, Animal> map = list.stream().collect(Collectors.toMap(Animal::getId, animal -> animal));
+        return map;
+    }
+
+    public Map<Integer, Animal> convertListWithGuava(List<Animal> list) {
+
+        Map<Integer, Animal> map = Maps.uniqueIndex(list, Animal::getId);
+        return map;
+    }
+
+    public Map<Integer, Animal> convertListWithApacheCommons1(List<Animal> list) {
+
+        Map<Integer, Animal> map = new HashMap<Integer, Animal>();
+
+        IterableUtils.forEach(list, animal -> {
+            map.put(animal.getId(), animal);
+        });
+
+        return map;
+    }
+
+    public Map<Integer, Animal> convertListWithApacheCommons2(List<Animal> list) {
+
+        Map<Integer, Animal> map = new HashMap<Integer, Animal>();
+
+        MapUtils.populateMap(map, list, Animal::getId);
+
+        return map;
+    }
+}

core-java-8/src/test/java/com/baeldung/convertlisttomap/ConvertListToMapServiceUnitTest.java

@@ -0,0 +1,73 @@
+package com.baeldung.convertlisttomap;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.*;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+
+import org.junit.Before;
+import org.junit.Test;
+
+public class ConvertListToMapServiceUnitTest {
+    List<Animal> list;
+
+    private ConvertListToMapService convertListService;
+
+    @Before
+    public void init() {
+        this.convertListService = new ConvertListToMapService();
+        this.list = new ArrayList<>();
+
+        Animal cat = new Animal(1, "Cat");
+        list.add(cat);
+        Animal dog = new Animal(2, "Dog");
+        list.add(dog);
+        Animal pig = new Animal(3, "Pig");
+        list.add(pig);
+        Animal cow = new Animal(4, "Cow");
+        list.add(cow);
+        Animal goat = new Animal(5, "Goat");
+        list.add(goat);
+    }
+
+    @Test
+    public void givenAList_whenConvertBeforeJava8_thenReturnMapWithTheSameElements() {
+
+        Map<Integer, Animal> map = convertListService.convertListBeforeJava8(list);
+
+        assertThat(map.values(), containsInAnyOrder(list.toArray()));
+    }
+
+    @Test
+    public void givenAList_whenConvertAfterJava8_thenReturnMapWithTheSameElements() {
+
+        Map<Integer, Animal> map = convertListService.convertListAfterJava8(list);
+
+        assertThat(map.values(), containsInAnyOrder(list.toArray()));
+    }
+
+    @Test
+    public void givenAList_whenConvertWithGuava_thenReturnMapWithTheSameElements() {
+
+        Map<Integer, Animal> map = convertListService.convertListWithGuava(list);
+
+        assertThat(map.values(), containsInAnyOrder(list.toArray()));
+    }
+
+    @Test
+    public void givenAList_whenConvertWithApacheCommons1_thenReturnMapWithTheSameElements() {
+
+        Map<Integer, Animal> map = convertListService.convertListWithApacheCommons1(list);
+
+        assertThat(map.values(), containsInAnyOrder(list.toArray()));
+    }
+
+    @Test
+    public void givenAList_whenConvertWithApacheCommons2_thenReturnMapWithTheSameElements() {
+
+        Map<Integer, Animal> map = convertListService.convertListWithApacheCommons2(list);
+
+        assertThat(map.values(), containsInAnyOrder(list.toArray()));
+    }
+}