集合判空CollectionUtils.isEmpty()

先了解集合

刚创建出来的List长度为0，但不为null

        List strList2 = new ArrayList<>();
        System.out.println(strList2 == null);//false
        strList2=null;
        System.out.println(strList2 == null);//true
        System.out.println(CollectionUtils.isEmpty(strList2));//true

 CollectionUtils.isEmpty()可以同时判空和长度，不会报空指针异常

 

if (images == null || images.size() == 0)   //原


if (CollectionUtils.isEmpty(images))    //now

 

List.isEmpty()与CollectionUtils.isEmpty的区别

List.isEmpty()发现当list为null的时候，list.isEmpty是会报空指针的，而CollectionUtils.isEmpty则不会。

package com.daylywork.study;

import org.apache.commons.collections.CollectionUtils;

import java.util.ArrayList;
import java.util.List;

public class CollectionandListIsEmepty {
    public static void main(String[] args){
        List listone = new ArrayList();
        System.out.println("CollectionUtils:"+CollectionUtils.isEmpty(listone));
        System.out.println("List:"+listone.isEmpty());
        listone=null;
        System.out.println("CollectionUtils:"+CollectionUtils.isEmpty(listone));
        System.out.println("List:"+listone.isEmpty());
    }
}

CollectionUtils:true
List:true
CollectionUtils:true
Exception in thread "main" java.lang.NullPointerException
	at com.daylywork.study.CollectionandListIsEmepty.main(CollectionandListIsEmepty.java:15)

Process finished with exit code 1