依赖关系

<!-- https://mvnrepository.com/artifact/org.apache.commons/commons-collections4 -->
<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-collections4</artifactId>
    <version>4.4</version>
</dependency>

代码结构

// 判空
CollectionUtils.isEmpty(collA);   // return (coll == null || coll.isEmpty())
CollectionUtils.isNotEmpty(list)

// 交集
CollectionUtils.retainAll(collA, collB);

List list1 = Arrays.asList(1,2,3,7);
List list2 = Arrays.asList(1,2,3,4,5,6);
System.out.println(CollectionUtils.retainAll(list1,list2)); // [1, 2, 3]

// 并集
CollectionUtils.union(collA, collB);

List list1 = Arrays.asList(1,2,3,7);
List list2 = Arrays.asList(1,2,3,4,5,6);
System.out.println(CollectionUtils.union(list1,list2));  // [1, 2, 3, 4, 5, 6, 7]

// 差集
CollectionUtils.subtract(collA, collB);

List list1 = Arrays.asList(1,2,3,7);
List list2 = Arrays.asList(1,2,3,4,5,6);
System.out.println(CollectionUtils.subtract(list1,list2));  // [7]

// 交集的补集
CollectionUtils.disjunction(listA,listB)

List list1 = Arrays.asList(1,2,3,7);
List list2 = Arrays.asList(1,2,3,4,5,6);
System.out.println(CollectionUtils.disjunction(list1,list2));  // [4, 5, 6, 7]

// 不可修改的集合 
Collection unmodifiableCollection(Collection collection)

// 判等
CollectionUtils.isEqualCollection(collA, collB);