How to convert List of a POJO to Map<String,List> in Java Stream?

[uSy62nMkdH]

List<User> to Map<String,List<User>>

[ebony0319]

what's the key?

[jorneyr]

users.stream().collect(Collectors.toMap(User::getUsername, u -> u, (o, n) -> o));

[anakinsky]

users.stream().collect(Collectors.groupingBy(User::getKey);

[Aresxue]

users.stream().collect(Collectors.groupingBy(User::getKey);

[KingOfUSA]

2 楼的写法好点，当 key 有重复的时候可以容错

[selca]

https://www.google.com/search?q=site%3Astackoverflow.com+How+to+convert+List+of+a+POJO+to+Map%3CString%2CList%3E+in+Java+Stream%3F&rlz=1C1GCEU_zh-CNUS1000US1000&oq=site%3Astackoverflow.com+How+to+convert+List+of+a+POJO+to+Map%3CString%2CList%3E+in+Java+Stream%3F&aqs=chrome..69i57j69i58.9674j0j1&sourceid=chrome&ie=UTF-8

[selca]

@selca #6 问题都是抄的

[lazyfighter]

@KingOfUSA bug 了，看清楚楼主的需求， 二楼的返回值是啥？

[KingOfUSA]

@lazyfighter 啊，我错了，，，

[xuanbg]

3 楼正解，就是按 User 对象的某个字段分组，然后以分组字段的值为 key 把对应分组的内容放进 value 。