我有一个List<Valuta>,可以表示(简化)JSON样式:
I have a List<Valuta> which can be represented (simplified) JSON-style:
[{codice = EUR,描述=欧元,比率= 1},{codice = USD, description =美元,比率= 1.1}]
[ { codice=EUR, description=Euro, ratio=1 }, { codice=USD, description=Dollars, ratio=1.1 } ]
我想像这样在Map<String, Valuta>中对其进行转换:
I want to transform that in a Map<String, Valuta> like this:
{EUR = {codice = EUR,描述=欧元,比率= 1},USD = {codice = USD, description =美元,比率= 1.1}}
{ EUR={ codice=EUR, description=Euro, ratio=1 }, USD={ codice=USD, description=Dollars, ratio=1.1 }}
我写了这样的一句话:
getValute().stream().collect(Collectors.groupingBy(Valuta::getCodice));但是这会返回Map<String, List<Valuta>>而不是我所需要的.
but this returns a Map<String, List<Valuta>> instead of what I need.
我想mapping()函数对我有用,但是不知道如何.
I suppose mapping() function would work for me, but don't know how.
推荐答案实际上,您需要在此处使用Collectors.toMap而不是Collectors.groupingBy:
Actually, you need to use Collectors.toMap here instead of Collectors.groupingBy:
Map<String, Valuta> map = getValute().stream() .collect(Collectors.toMap(Valuta::getCodice, Function.identity()));groupingBy 用于基于分组功能对Stream的元素进行分组.默认情况下,与分组功能具有相同结果的2个Stream元素将被收集到List中.
toMap 会将元素收集到Map中,其中键是应用给定键映射器的结果,而值是应用值映射器的结果.请注意,默认情况下toMap会在遇到重复项时引发异常.
toMap will collect the elements into a Map where the key is the result of applying a given key mapper and the value is the result of applying a value mapper. Note that toMap, by default, will throw an exception if a duplicate is encountered.
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