feat: Java 8 – Convert List to Map.

src/main/java/br/com/somejava8examples/commons/entities/Hosting.java

@@ -0,0 +1,64 @@
+package br.com.somejava8examples.commons.entities;
+
+import java.util.Objects;
+
+public class Hosting {
+
+    private int Id;
+    private String name;
+    private long websites;
+
+    public Hosting(int id, String name, long websites) {
+        Id = id;
+        this.name = name;
+        this.websites = websites;
+    }
+
+    public int getId() {
+        return Id;
+    }
+
+    public void setId(int id) {
+        Id = id;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public long getWebsites() {
+        return websites;
+    }
+
+    public void setWebsites(long websites) {
+        this.websites = websites;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (!(o instanceof Hosting)) return false;
+        Hosting hosting = (Hosting) o;
+        return getId() == hosting.getId() &&
+                getWebsites() == hosting.getWebsites() &&
+                Objects.equals(getName(), hosting.getName());
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(getId(), getName(), getWebsites());
+    }
+
+    @Override
+    public String toString() {
+        return "Hosting{" +
+                "Id=" + Id +
+                ", name='" + name + '\'' +
+                ", websites=" + websites +
+                '}';
+    }
+}

src/main/java/br/com/somejava8examples/map/ConvertListToMapService.java

@@ -0,0 +1,92 @@
+package br.com.somejava8examples.map;
+
+import br.com.somejava8examples.commons.entities.Hosting;
+import org.springframework.stereotype.Service;
+
+import java.util.*;
+import java.util.stream.Collectors;
+
+@Service
+public class ConvertListToMapService {
+
+    private List<Hosting> getList() {
+        List<Hosting> list = new ArrayList<>();
+        list.add(new Hosting(1, "liquidweb.com", 80000));
+        list.add(new Hosting(2, "linode.com", 90000));
+        list.add(new Hosting(3, "digitalocean.com", 120000));
+        list.add(new Hosting(4, "aws.amazon.com", 200000));
+        list.add(new Hosting(5, "google.com", 1));
+        return list;
+    }
+
+    public Map<Integer, String> listToMapCollectorsToMap() {
+        List<Hosting> list = getList();
+
+        // key = id, value - websites
+        Map<Integer, String> result1 = list.stream().collect(Collectors.toMap(Hosting::getId, Hosting::getName));
+
+        System.out.println("Result 1 : " + result1);
+
+        // key = name, value - websites
+        Map<String, Long> result2 = list.stream().collect(Collectors.toMap(Hosting::getName, Hosting::getWebsites));
+
+        System.out.println("Result 2 : " + result2);
+
+        // Same with result1, just different syntax
+        // key = id, value = name
+        Map<Integer, String> result3 = list.stream().collect(Collectors.toMap(x -> x.getId(), x -> x.getName()));
+
+        System.out.println("Result 3 : " + result3);
+
+        return result3;
+    }
+
+    public Map<String, Long> listToMapDuplicatedKeyDuplicated() {
+        List<Hosting> list = getList();
+
+        list.add(new Hosting(6, "linode.com", 100000)); // new line
+
+        // key = name, value - websites , but the key 'linode' is duplicated!?
+        Map<String, Long> result1 = list.stream().collect(Collectors.toMap(Hosting::getName, Hosting::getWebsites));
+
+        System.out.println("Result 1 : " + result1);
+
+        return result1;
+    }
+
+    public Map<String, Long> listToMapDuplicatedKeyMerge() {
+        List<Hosting> list = getList();
+
+        list.add(new Hosting(6, "linode.com", 100000)); // new line
+
+        Map<String, Long> result1 = list.stream().collect(
+                Collectors.toMap(Hosting::getName, Hosting::getWebsites,
+                        (oldValue, newValue) -> oldValue
+                )
+        );
+
+        System.out.println("Result 1 : " + result1);
+
+        return result1;
+    }
+
+    public Map listToMapSortCollect() {
+        List<Hosting> list = getList();
+        list.add(new Hosting(6, "linode.com", 100000));
+
+        //example 1
+        Map result1 = list.stream()
+                .sorted(Comparator.comparingLong(Hosting::getWebsites).reversed())
+                .collect(
+                        Collectors.toMap(
+                                Hosting::getName, Hosting::getWebsites, // key = name, value = websites
+                                (oldValue, newValue) -> oldValue,       // se a mesma chave, pegue a chave antiga
+                                LinkedHashMap::new                      // returns a LinkedHashMap, keep order
+                        ));
+
+        System.out.println("Result 1 : " + result1);
+
+        return result1;
+    }
+
+}

src/test/java/br/com/somejava8examples/map/ConvertListToMapTest.java

@@ -0,0 +1,42 @@
+package br.com.somejava8examples.map;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.context.ActiveProfiles;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+@SpringBootTest
+@ActiveProfiles("test")
+public class ConvertListToMapTest {
+
+    @Autowired
+    private ConvertListToMapService service;
+
+    @Test
+    public void listToMapCollectorsToMapTest() {
+        assertFalse(service.listToMapCollectorsToMap().isEmpty(), "List is empty");
+    }
+
+    @Test
+    public void listToMapDuplicatedKeyDuplicatedTest() {
+        Exception exception = assertThrows(IllegalStateException.class, () -> {service.listToMapDuplicatedKeyDuplicated();});
+
+        String expectedMessage = "Duplicate key linode.com (attempted merging values 90000 and 100000)";
+        String actualMessage = exception.getMessage();
+
+        assertEquals(actualMessage, expectedMessage);
+    }
+
+    @Test
+    public void listToMapDuplicatedKeyMergeTest() {
+        assertFalse(service.listToMapDuplicatedKeyMerge().isEmpty(), "List is empty");
+    }
+
+    @Test
+    public void listToMapSortCollectTest() {
+        assertFalse(service.listToMapSortCollect().isEmpty(), "List is empty");
+    }
+
+}

src/test/java/br/com/somejava8examples/stream/StreamHasAlreadyBeenOperatedUponOrClosedTest.java

@@ -18,11 +18,8 @@ public class StreamHasAlreadyBeenOperatedUponOrClosedTest {
     private StreamHasAlreadyBeenOperatedUponOrClosedService service;
 
     @Test
-    @DisplayName("Test Spring @Autowired Integration")
     public void streamIsClosedTest() {
-        Exception exception = assertThrows(IllegalStateException.class, () -> {
-            service.streamIsClosed();
-        });
+        Exception exception = assertThrows(IllegalStateException.class, () -> {service.streamIsClosed();});
 
         String expectedMessage = "stream has already been operated upon or closed";
         String actualMessage = exception.getMessage();