如何在Java8中将Map流转换为TreeMap [英] How to convert Stream of Map into TreeMap in Java8

问题描述

我有一个接收地图流的方法，应该返回一个TreeMap

I have a method that takes in a Stream of map and should return a TreeMap

public TreeMap<String, String> buildTreeMap(Stream<Map<String, String>> inStream) {
   return stream.collect(toMap(???));
}

如何让它返回TreeMap？

How can I make it return a TreeMap?

推荐答案

stream.collect(TreeMap::new, TreeMap::putAll, 
    (map1, map2) -> { map1.putAll(map2); return map1; });

...假设您想将所有地图合并为一张大地图。

...assuming you want to combine all the maps into one big map.

如果您想要为同一个键合并值的语义不同，请执行以下操作：

If you want different semantics for merging values for the same key, do something like

stream.flatMap(map -> map.entrySet().stream())
   .collect(toMap(
       Entry::getKey, Entry::getValue, (v1, v2) -> merge(v1, v2), TreeMap::new));

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