add method

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

@@ -246,7 +246,7 @@ public class ListUtil {
 		// 每页条目数大于总数直接返回所有
 		if (resultSize <= pageSize) {
 			if (pageNo < (PageUtil.getFirstPageNo() + 1)) {
-				return Collections.unmodifiableList(list);
+				return unmodifiable(list);
 			} else {
 				// 越界直接返回空
 				return new ArrayList<>(0);
@@ -262,11 +262,11 @@ public class ListUtil {
 		if (startEnd[1] > resultSize) {
 			startEnd[1] = resultSize;
 			if (startEnd[0] > startEnd[1]) {
-				return empty();
+				return new ArrayList<>(0);
 			}
 		}
 
-		return list.subList(startEnd[0], startEnd[1]);
+		return sub(list, startEnd[0], startEnd[1]);
 	}
 
 	/**
@@ -366,7 +366,8 @@ public class ListUtil {
 	}
 
 	/**
-	 * 截取集合的部分
+	 * 截取集合的部分<br>
+	 * 此方法与{@link List#subList(int, int)} 不同在于子列表是新的副本，操作子列表不会影响原列表。
 	 *
 	 * @param <T>   集合元素类型
 	 * @param list  被截取的数组
@@ -407,8 +408,8 @@ public class ListUtil {
 			end = size;
 		}
 
-		if (step <= 1) {
-			return list.subList(start, end);
+		if (step < 1) {
+			step = 1;
 		}
 
 		final List<T> result = new ArrayList<>();

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

@@ -101,4 +101,15 @@ public class ListUtilTest {
 		int[] d1 = ListUtil.page(0,8,a).stream().mapToInt(Integer::valueOf).toArray();
 		Assert.assertArrayEquals(new int[]{1,2,3,4,5},d1);
 	}
+
+	@Test
+	public void subTest(){
+		final List<Integer> of = ListUtil.of(1, 2, 3, 4);
+		final List<Integer> sub = ListUtil.sub(of, 2, 4);
+		sub.remove(0);
+
+		// 对子列表操作不影响原列表
+		Assert.assertEquals(4, of.size());
+		Assert.assertEquals(1, sub.size());
+	}
 }

hutool-core/src/test/java/cn/hutool/core/util/IdUtilTest.java

@@ -17,7 +17,7 @@ import java.util.concurrent.CountDownLatch;
 
 /**
  * {@link IdUtil} 单元测试
- * 
+ *
  * @author looly
  *
  */
@@ -31,12 +31,12 @@ public class IdUtilTest {
 		String randomUUID = IdUtil.randomUUID();
 		Assert.assertEquals(36, randomUUID.length());
 	}
-	
+
 	@Test
 	public void fastUUIDTest() {
 		String simpleUUID = IdUtil.fastSimpleUUID();
 		Assert.assertEquals(32, simpleUUID.length());
-		
+
 		String randomUUID = IdUtil.fastUUID();
 		Assert.assertEquals(36, randomUUID.length());
 	}
@@ -60,25 +60,26 @@ public class IdUtilTest {
 		}
 		Console.log(timer.interval());
 	}
-	
+
 	@Test
 	public void objectIdTest() {
 		String id = IdUtil.objectId();
 		Assert.assertEquals(24, id.length());
 	}
-	
+
 	@Test
 	public void createSnowflakeTest() {
 		Snowflake snowflake = IdUtil.createSnowflake(1, 1);
 		long id = snowflake.nextId();
 		Assert.assertTrue(id > 0);
 	}
-	
+
 	@Test
+	@Ignore
 	public void snowflakeBenchTest() {
 		final Set<Long> set = new ConcurrentHashSet<>();
 		final Snowflake snowflake = IdUtil.createSnowflake(1, 1);
-		
+
 		//线程数
 		int threadCount = 100;
 		//每个线程生成的ID数
@@ -94,7 +95,7 @@ public class IdUtilTest {
 				latch.countDown();
 			});
 		}
-		
+
 		//等待全部线程结束
 		try {
 			latch.await();
@@ -103,11 +104,12 @@ public class IdUtilTest {
 		}
 		Assert.assertEquals(threadCount * idCountPerThread, set.size());
 	}
-	
+
 	@Test
+	@Ignore
 	public void snowflakeBenchTest2() {
 		final Set<Long> set = new ConcurrentHashSet<>();
-		
+
 		//线程数
 		int threadCount = 100;
 		//每个线程生成的ID数
@@ -123,7 +125,7 @@ public class IdUtilTest {
 				latch.countDown();
 			});
 		}
-		
+
 		//等待全部线程结束
 		try {
 			latch.await();