jdk8 Collectors.toMap中的value为null时报NullPointerException

川长思鸟来 2021-09-24 12:06 442阅读 0赞

一、问题说明

如果Map中有个键值对的value为null，在调用Collectors.toMap时会报NullPointerException

代码如下：

public static void main(String[] args) {
    	Map<String, String> map = new HashMap<>();
    	map.put("aaa", "111");
    	map.put("bbb", "222");
    	map.put("ccc", null);
    
    	Map<String, String> resultMap;
    	resultMap = map.entrySet().stream().collect(Collectors.toMap(entry -> entry.getKey(), entry -> entry.getValue()));
    	System.out.println(resultMap);
    }

二、问题解决

源码中可以看到，明确要求value不能为null

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTA5OTk4MDk_size_16_color_FFFFFF_t_70][]

解决思路：当value为null时，更换成""就行了

将上面的代码修改成：

public static void main(String[] args) {
    	Map<String, String> map = new HashMap<>();
    	map.put("aaa", "111");
    	map.put("bbb", "222");
    	map.put("ccc", null);
    
    	Map<String, String> resultMap;
    	resultMap = map.entrySet().stream().collect(Collectors.toMap(entry -> entry.getKey(),
    			entry -> Optional.ofNullable(entry.getValue()).orElse("")));
    	System.out.println(resultMap);
    }

参考链接：

[https://blog.csdn.net/wysnxzm/article/details/81260073][https_blog.csdn.net_wysnxzm_article_details_81260073]

[https://blog.csdn.net/qq\_40223688/article/details/104264461][https_blog.csdn.net_qq_40223688_article_details_104264461]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTA5OTk4MDk_size_16_color_FFFFFF_t_70]: /images/20210923/bd60b0f6e4044088916f0272b871d87f.png
[https_blog.csdn.net_wysnxzm_article_details_81260073]: https://blog.csdn.net/wysnxzm/article/details/81260073
[https_blog.csdn.net_qq_40223688_article_details_104264461]: https://blog.csdn.net/qq_40223688/article/details/104264461