isEmpty对集合校验null

需要注意使用**isEmpty**可能会出现空指针异常情况，推荐使用CollectionUtils.isEmpty

  public static void main(String[] args) {
        /*----------------【Start】isEmpty方法检查-----------------*/
        List<String> strList1 = Lists.newArrayList();
        System.out.println(CollectionUtils.isEmpty(strList1));//true
        System.out.println(CollectionUtils.isEmpty(new ArrayList()));//true
        System.out.println(strList1 == null);//false
        System.out.println(strList1.size());//0
        List<String> strList2 = new ArrayList<>();
        System.out.println(strList2 == null);//false
        strList2 = null;
        System.out.println(strList2 == null);//true
        System.out.println(CollectionUtils.isEmpty(strList2));//true
        /*----------------【END】isEmpty方法检查-----------------*/
        List<String> strList3 = Lists.newArrayList();
        List<String> strings = new ArrayList<>();
        System.out.println("strList3 = " + strList3.isEmpty());//true
        System.out.println("strings.isEmpty() = " + strings.isEmpty());//true
        strings = null;
        System.out.println("strings.isEmpty() null = " + strings.isEmpty());//空指针异常
    }

总结

1：刚创建出来的List长度为0，但不为null

2：CollectionUtils.isEmpty()方法可以检查null和长度为0的list