add method

CHANGELOG.md

@@ -2,7 +2,7 @@
 # 🚀Changelog
 
 -------------------------------------------------------------------------------------------------------------
-# 5.8.0.M2 (2022-03-30)
+# 5.8.0.M2 (2022-03-31)
 
 ### ❌不兼容特性
 * 【extra  】     【可能兼容问题】BeanCopierCache的key结构变更
@@ -10,6 +10,7 @@
 ### 🐣新特性
 * 【core   】     MapUtil增加entry、ofEntries方法
 * 【core   】     ZipWriter增加add方法重载
+* 【core   】     IterUtil增加filtered，增加FilterIter（issue#2228）
 
 ### 🐞Bug修复
 * 【core   】     IdcardUtil#getCityCodeByIdCard位数问题（issue#2224@Github）

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

@@ -0,0 +1,96 @@
+package cn.hutool.core.collection;
+
+import cn.hutool.core.lang.Assert;
+import cn.hutool.core.lang.Filter;
+
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+
+/**
+ * 包装 {@link Iterator}并根据{@link Filter}定义，过滤元素输出<br>
+ * 类实现来自Apache Commons Collection
+ *
+ * @author apache commons, looly
+ * @since 5.8.0
+ */
+public class FilterIter<E> implements Iterator<E> {
+
+	private final Iterator<? extends E> iterator;
+	private final Filter<? super E> filter;
+
+	/**
+	 * 下一个元素
+	 */
+	private E nextObject;
+	/**
+	 * 标记下一个元素是否被计算
+	 */
+	private boolean nextObjectSet = false;
+
+	/**
+	 * 构造
+	 *
+	 * @param iterator 被包装的{@link Iterator}
+	 * @param filter   过滤函数，{@code null}表示不过滤
+	 */
+	public FilterIter(final Iterator<? extends E> iterator, final Filter<? super E> filter) {
+		this.iterator = Assert.notNull(iterator);
+		this.filter = filter;
+	}
+
+	@Override
+	public boolean hasNext() {
+		return nextObjectSet || setNextObject();
+	}
+
+	@Override
+	public E next() {
+		if (false == nextObjectSet && false == setNextObject()) {
+			throw new NoSuchElementException();
+		}
+		nextObjectSet = false;
+		return nextObject;
+	}
+
+	@Override
+	public void remove() {
+		if (nextObjectSet) {
+			throw new IllegalStateException("remove() cannot be called");
+		}
+		iterator.remove();
+	}
+
+	/**
+	 * 获取被包装的{@link Iterator}
+	 *
+	 * @return {@link Iterator}
+	 */
+	public Iterator<? extends E> getIterator() {
+		return iterator;
+	}
+
+	/**
+	 * 获取过滤函数
+	 *
+	 * @return 过滤函数，可能为{@code null}
+	 */
+	public Filter<? super E> getFilter() {
+		return filter;
+	}
+
+	/**
+	 * 设置下一个元素，如果存在返回{@code true}，否则{@code false}
+	 */
+	private boolean setNextObject() {
+		while (iterator.hasNext()) {
+			final E object = iterator.next();
+			if (null != filter && filter.accept(object)) {
+				nextObject = object;
+				nextObjectSet = true;
+				return true;
+			}
+		}
+		return false;
+	}
+
+}

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

@@ -745,17 +745,20 @@ public class IterUtil {
 	 * @since 5.7.22
 	 */
 	public static <E> List<E> filterToList(Iterator<E> iter, Filter<E> filter) {
-		final List<E> result = new ArrayList<>();
-		if (null != iter) {
-			E ele;
-			while (iter.hasNext()) {
-				ele = iter.next();
-				if (null == filter || filter.accept(ele)) {
-					result.add(ele);
-				}
-			}
-		}
-		return result;
+		return toList(filtered(iter, filter));
+	}
+
+	/**
+	 * 获取一个新的 {@link FilterIter}，用于过滤指定元素
+	 *
+	 * @param iterator  被包装的 {@link Iterator}
+	 * @param filter 过滤断言，当{@link Filter#accept(Object)}为{@code true}时保留元素，{@code false}抛弃元素
+	 * @param <E>       元素类型
+	 * @return {@link FilterIter}
+	 * @since 5.8.0
+	 */
+	public static <E> FilterIter<E> filtered(final Iterator<? extends E> iterator, final Filter<? super E> filter) {
+		return new FilterIter<>(iterator, filter);
 	}
 
 	/**

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

@@ -24,7 +24,7 @@ public class TransIter<F, T> implements Iterator<T> {
 	 * @param backingIterator 源{@link Iterator}
 	 * @param func            转换函数
 	 */
-	public TransIter(Iterator<? extends F> backingIterator, Function<? super F, ? extends T> func) {
+	public TransIter(final Iterator<? extends F> backingIterator, final Function<? super F, ? extends T> func) {
 		this.backingIterator = Assert.notNull(backingIterator);
 		this.func = Assert.notNull(func);
 	}

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

@@ -103,4 +103,37 @@ public class IterUtilTest {
 		private String carNumber;
 		private String carName;
 	}
+
+	@Test
+	public void filterTest(){
+		List<String> obj2 = ListUtil.toList("3");
+		List<String> obj = ListUtil.toList("1", "3");
+
+		IterUtil.filter(obj.iterator(), obj2::contains);
+
+		Assert.assertEquals(1, obj.size());
+		Assert.assertEquals("3", obj.get(0));
+	}
+
+	@Test
+	public void filteredTest(){
+		List<String> obj2 = ListUtil.toList("3");
+		List<String> obj = ListUtil.toList("1", "3");
+
+		final FilterIter<String> filtered = IterUtil.filtered(obj.iterator(), obj2::contains);
+
+		Assert.assertEquals("3", filtered.next());
+		Assert.assertFalse(filtered.hasNext());
+	}
+
+	@Test
+	public void filterToListTest(){
+		List<String> obj2 = ListUtil.toList("3");
+		List<String> obj = ListUtil.toList("1", "3");
+
+		final List<String> filtered = IterUtil.filterToList(obj.iterator(), obj2::contains);
+
+		Assert.assertEquals(1, filtered.size());
+		Assert.assertEquals("3", filtered.get(0));
+	}
 }