Enhance toList and add toSet in CollectionUtil (#25)

pom.xml

@@ -6,7 +6,7 @@
 
     <groupId>com.baidu.hugegraph</groupId>
     <artifactId>hugegraph-common</artifactId>
-    <version>1.6.2</version>
+    <version>1.6.3</version>
 
     <name>hugegraph-common</name>
     <url>https://github.com/hugegraph/hugegraph-common</url>
@@ -212,7 +212,7 @@
                         <manifestEntries>
                             <!-- Must be on one line, otherwise the automatic
                                  upgrade script cannot replace the version number -->
-                            <Implementation-Version>1.6.2.0</Implementation-Version>
+                            <Implementation-Version>1.6.3.0</Implementation-Version>
                         </manifestEntries>
                     </archive>
                 </configuration>

src/main/java/com/baidu/hugegraph/util/CollectionUtil.java

@@ -33,19 +33,33 @@
 
 public final class CollectionUtil {
 
+    public static <T> Set<T> toSet(Object object) {
+        E.checkNotNull(object, "object");
+        Set<T> set = InsertionOrderUtil.newSet();
+        fillCollection(set, object);
+        return set;
+    }
+
+    public static <T> List<T> toList(Object object) {
+        E.checkNotNull(object, "object");
+        List<T> list = new ArrayList<>();
+        fillCollection(list, object);
+        return list;
+    }
+
     @SuppressWarnings("unchecked")
-    public static <T> List<T> toList(Object array) {
-        E.checkNotNull(array, "array");
-        E.checkArgument(array.getClass().isArray(),
-                        "The parameter of toList() must be an array: '%s'",
-                        array.getClass().getSimpleName());
-
-        int length = Array.getLength(array);
-        List<T> list = new ArrayList<>(length);
-        for (int i = 0; i < length; i++) {
-            list.add((T) Array.get(array, i));
+    private static <T> void fillCollection(Collection<T> collection,
+                                           Object object) {
+        if (object.getClass().isArray()) {
+            int length = Array.getLength(object);
+            for (int i = 0; i < length; i++) {
+                collection.add((T) Array.get(object, i));
+            }
+        } else if (object instanceof Collection) {
+            collection.addAll((Collection<T>) object);
+        } else {
+            collection.add((T) object);
         }
-        return list;
     }
 
     public static <T> boolean prefixOf(List<T> prefix, List<T> all) {

src/main/java/com/baidu/hugegraph/version/CommonVersion.java

@@ -27,5 +27,5 @@ public class CommonVersion {
 
     // The second parameter of Version.of() is for all-in-one JAR
     public static final Version VERSION = Version.of(CommonVersion.class,
-                                                     "1.6.2");
+                                                     "1.6.3");
 }

src/test/java/com/baidu/hugegraph/unit/util/CollectionUtilTest.java

@@ -37,8 +37,37 @@
 
 public class CollectionUtilTest extends BaseUnitTest {
 
+    @Test
+    public void testToSet() {
+        Assert.assertThrows(NullPointerException.class, () -> {
+            CollectionUtil.toSet(null);
+        });
+
+        Object array1 = new Integer[]{1, 2, 3};
+        Assert.assertEquals(ImmutableSet.of(1, 2, 3),
+                            CollectionUtil.toSet(array1));
+
+        Object array2 = new String[]{"1", "2", "3"};
+        Assert.assertEquals(ImmutableSet.of("1", "2", "3"),
+                            CollectionUtil.toSet(array2));
+
+        Set<Integer> set = ImmutableSet.of(1, 2, 3);
+        Assert.assertEquals(ImmutableSet.of(1, 2, 3),
+                            CollectionUtil.toSet(set));
+
+        List<Integer> list = ImmutableList.of(1, 2, 3);
+        Assert.assertEquals(ImmutableSet.of(1, 2, 3),
+                            CollectionUtil.toSet(list));
+
+        Assert.assertEquals(ImmutableSet.of(1), CollectionUtil.toSet(1));
+    }
+
     @Test
     public void testToList() {
+        Assert.assertThrows(NullPointerException.class, () -> {
+            CollectionUtil.toList(null);
+        });
+
         Object array1 = new Integer[]{1, 2, 3};
         Assert.assertEquals(ImmutableList.of(1, 2, 3),
                             CollectionUtil.toList(array1));
@@ -47,13 +76,16 @@ public void testToList() {
         Assert.assertEquals(ImmutableList.of("1", "2", "3"),
                             CollectionUtil.toList(array2));
 
-        Assert.assertThrows(NullPointerException.class, () -> {
-            CollectionUtil.toList(null);
-        });
+        Set<Integer> set = ImmutableSet.of(1, 2, 3);
+        Assert.assertEquals(ImmutableList.of(1, 2, 3),
+                            CollectionUtil.toList(set));
 
-        Assert.assertThrows(IllegalArgumentException.class, () -> {
-            CollectionUtil.toList("123");
-        });
+        List<Integer> list = ImmutableList.of(1, 2, 3);
+        Assert.assertEquals(ImmutableList.of(1, 2, 3),
+                            CollectionUtil.toList(list));
+
+        Assert.assertEquals(ImmutableList.of("123"),
+                            CollectionUtil.toList("123"));
     }
 
     @Test