如何使用streams Java 8按键分组列表并拆分值

Question

我需要对ABC列表进行分组，同时我还想拆分值。输入：

List<ABC> list = new ArrayList<>();

ABC A1 = new ABC();
A1.setName("OO");
A1.setVal("OO111,OO222,OO333"); // split this while grouping
list.add(A1);

ABC A2 = new ABC();
A2.setName("OO");
A2.setVal("OO1");
list.add(A2);

ABC A3 = new ABC();
A3.setName("YY");
A3.setVal("1333,11444");
list.add(A3);

Output:

```java
Map<String, List<String>> postsPerType;
//Group by Name: ex: OO & YY. Split the Value by "," and add it to list
     Key: 00 Values: List: "OO111","OO222","OO333","OO1"
     Key: YY Values: List: "1333","11444"

请建议，谢谢。

Answer 1

如果您使用Java9+，可以使用collectors.flatmapping()作为按的下游分组：

list.stream().collect(Collectors.groupingBy(ABC::getName,
                    Collectors.flatMapping(a -> Arrays.stream(a.getVal().split(",")), 
                                           Collectors.toList())));

这应该会产生你想要的结果。