如何扁平化HashMap? [英] How to Flatten a HashMap?

问题描述

我以这种形式嵌套了HashMap:

{key1=val1, key2=val2, 
    key3=[
            {key4=val4, key5=val5}, 
            {key6=val6, key7=val7} 
        ]
}

我现在想展平该地图，以使所有条目都处于同一级别:

I now want to flatten that map, so that all entries are on the same level:

{key1=val1, key2=val2, key4=val4, key5=val5,key6=val6, key7=val7}

---

当我尝试

---

When I try

map.values().forEach(map.get("key3")::addAll);

如本文中所述 所述，我收到以下错误消息:

as described in this post, I get the following error:

invalid method reference
  cannot find symbol
    symbol:   method addAll(T)
    location: class Object
  where T is a type-variable:
    T extends Object declared in interface Iterable

---

是否有任何通用的方法来扁平化任何给定的Map?

推荐答案

不确定我是否正确理解了这个问题，但是类似的方法可能有效. 尚未检查所有语法，因此某处可能存在一些错误.

Not sure if I understood the question correctly, but something like this might work. Haven't checked all the syntax yet, so there might be some mistake somewhere.

Stream<Map.Entry<String, String>> flatten(Map<String, Object> map) {
  return map.entrySet()
            .stream()
            .flatMap(this::extractValue);         
}

Stream<Map.Entry<String, String>> extractValue(Map.Entry<String, Object> entry) {
   if (entry.getValue() instanceof String) {
      return Stream.of(new AbstractMap.SimpleEntry(entry.getKey(), (String) entry.getValue()));
   } else if (entry.getValue() instanceof Map) {
      return flatten((Map<String, Object>) entry.getValue());
   }
}

那么你可以做:

Map<String, String> flattenedMap = flatten(yourmap)
   .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));

这篇关于如何扁平化HashMap?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！