!750 CollUtil新增addIfAbsent方法

Merge pull request !750 from 这是一个腊鸡/v5-dev

hutool-core/src/main/java/cn/hutool/core/collection/CollUtil.java

@@ -2075,6 +2075,32 @@ public class CollUtil {
 		return IterUtil.toMap(null == values ? null : values.iterator(), map, keyFunc, valueFunc);
 	}
 
+	/**
+	 * 一个对象不为空且不存在于该集合中时，加入到该集合中<br>
+	 * <pre>
+	 *     null, null => false
+	 *     [], null => false
+	 *     null, "123" => false
+	 *     ["123"], "123" => false
+	 *     [], "123" => true
+	 *     ["456"], "123" => true
+	 *     [Animal{"name": "jack"}], Dog{"name": "jack"} => true
+	 * </pre>
+	 * @param collection 被加入的集合
+	 * @param object 要添加到集合的对象
+	 * @param <T> 集合元素类型
+	 * @param <S> 要添加的元素类型【为集合元素类型的类型或子类型】
+	 * @return 是否添加成功
+	 * @author Cloud-Style
+	 */
+	public static <T, S extends T> boolean addIfAbsent(Collection<T> collection, S object) {
+		if (object == null || collection == null || collection.contains(object)) {
+			return false;
+		}
+
+		return collection.add(object);
+	}
+
 	/**
 	 * 将指定对象全部加入到集合中<br>
 	 * 提供的对象如果为集合类型，会自动转换为目标元素类型<br>

hutool-core/src/test/java/cn/hutool/core/collection/CollUtilTest.java

@@ -7,6 +7,9 @@ import cn.hutool.core.map.MapUtil;
 import cn.hutool.core.util.StrUtil;
 import lombok.AllArgsConstructor;
 import lombok.Data;
+import lombok.EqualsAndHashCode;
+import lombok.NoArgsConstructor;
+import lombok.ToString;
 import org.junit.Assert;
 import org.junit.Test;
 
@@ -745,6 +748,24 @@ public class CollUtilTest {
 		Assert.assertEquals("d", map.get("keyd"));
 	}
 
+	@Test
+	public void addIfAbsentTest() {
+		// 为false的情况
+		Assert.assertFalse(CollUtil.addIfAbsent(null, null));
+		Assert.assertFalse(CollUtil.addIfAbsent(CollUtil.newArrayList(), null));
+		Assert.assertFalse(CollUtil.addIfAbsent(null, "123"));
+		Assert.assertFalse(CollUtil.addIfAbsent(CollUtil.newArrayList("123"), "123"));
+		Assert.assertFalse(CollUtil.addIfAbsent(CollUtil.newArrayList(new Animal("jack", 20)),
+				new Animal("jack", 20)));
+
+		// 正常情况
+		Assert.assertTrue(CollUtil.addIfAbsent(CollUtil.newArrayList("456"), "123"));
+		Assert.assertTrue(CollUtil.addIfAbsent(CollUtil.newArrayList(new Animal("jack", 20)),
+				new Dog("jack", 20)));
+		Assert.assertTrue(CollUtil.addIfAbsent(CollUtil.newArrayList(new Animal("jack", 20)),
+				new Animal("tom", 20)));
+	}
+
 	@Test
 	public void mapToMapTest(){
 		final HashMap<String, String> oldMap = new HashMap<>();
@@ -951,4 +972,22 @@ public class CollUtilTest {
 		private String gender;
 		private Integer id;
 	}
+
+	@Data
+	@AllArgsConstructor
+	@NoArgsConstructor
+	static class Animal {
+		private String name;
+		private Integer age;
+	}
+
+	@ToString(callSuper = true)
+	@EqualsAndHashCode(callSuper = true)
+	@Data
+	static class Dog extends Animal {
+
+		public Dog(String name, Integer age) {
+			super(name, age);
+		}
+	}
 }