使用org.apache.commons.collections.CollectionUtils进行List与List比较

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集合判断：

例1: 判断集合是否为空:

CollectionUtils.isEmpty(null): true

CollectionUtils.isEmpty(new ArrayList()): true

CollectionUtils.isEmpty({a,b}): false

例2: 判断集合是否不为空:

CollectionUtils.isNotEmpty(null): false

CollectionUtils.isNotEmpty(new ArrayList()): false

CollectionUtils.isNotEmpty({a,b}): true

2个集合间的操作：

集合a: {1,2,3,3,4,5}

集合b: {3,4,4,5,6,7}

CollectionUtils.union(a, b)(并集): {1,2,3,3,4,4,5,6,7}

CollectionUtils.intersection(a, b)(交集): {3,4,5}

CollectionUtils.disjunction(a, b)(交集的补集): {1,2,3,4,6,7}

CollectionUtils.disjunction(b, a)(交集的补集): {1,2,3,4,6,7}

CollectionUtils.subtract(a, b)(A与B的差): {1,2,3}

CollectionUtils.subtract(b, a)(B与A的差): {4,6,7}