条目集上的Java 8流映射 [英] Java 8 stream map on entry set

问题描述

我正在尝试对Map对象中的每个条目执行映射操作.

I'm trying to perform a map operation on each entry in a Map object.

我需要在键上取一个前缀，然后将值从一种类型转换为另一种类型.我的代码从Map<String, String>获取配置条目并将其转换为Map<String, AttributeType>(AttributeType只是一个包含一些信息的类.进一步的解释与该问题无关.)

I need to take a prefix off the key and convert the value from one type to another. My code is taking configuration entries from a Map<String, String> and converting to a Map<String, AttributeType> (AttributeType is just a class holding some information. Further explanation is not relevant for this question.)

使用Java 8 Streams我能想到的最好的方法是:

The best I have been able to come up with using the Java 8 Streams is the following:

private Map<String, AttributeType> mapConfig(Map<String, String> input, String prefix) {
   int subLength = prefix.length();
   return input.entrySet().stream().flatMap((Map.Entry<String, Object> e) -> {
      HashMap<String, AttributeType> r = new HashMap<>();
      r.put(e.getKey().substring(subLength), AttributeType.GetByName(e.getValue()));
      return r.entrySet().stream();
   }).collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));
}

由于它是接口而无法构造Map.Entry，因此会导致创建单个条目Map实例并使用flatMap()，这看起来很丑.

Being unable to construct an Map.Entry due to it being an interface causes the creation of the single entry Map instance and the use of flatMap(), which seems ugly.

还有更好的选择吗?使用for循环执行此操作似乎更好:

Is there a better alternative? It seems nicer to do this using a for loop:

private Map<String, AttributeType> mapConfig(Map<String, String> input, String prefix) {
   Map<String, AttributeType> result = new HashMap<>(); 
   int subLength = prefix.length(); 
   for(Map.Entry<String, String> entry : input.entrySet()) {
      result.put(entry.getKey().substring(subLength), AttributeType.GetByName( entry.getValue()));
   }
   return result;
}

我应该避免使用Stream API吗?还是我错过了更好的方法?

Should I avoid the Stream API for this? Or is there a nicer way I have missed?

推荐答案

简单地将旧的for循环方式"转换为流:

Simply translating the "old for loop way" into streams:

private Map<String, String> mapConfig(Map<String, Integer> input, String prefix) {
    int subLength = prefix.length();
    return input.entrySet().stream()
            .collect(Collectors.toMap(
                   entry -> entry.getKey().substring(subLength), 
                   entry -> AttributeType.GetByName(entry.getValue())));
}

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