Java8:使用流将一个地图转换为另一张地图

问题描述

我需要将Java HashMap转换为TreeMap的实例(包括地图内容)

I need to convert a Java HashMap to an instance of TreeMap (including map contents)

HashMap<String, Object> src = ...;
TreeMap<String, Object> dest = src.entrySet().stream()
        .filter( ... )
        .collect(Collectors.toMap( ???, ???, ???, TreeMap::new));

我应该用什么代替???以便使此代码可编译?

What should I put in place of ??? to make this code compilable?

推荐答案

来自 :

 * @param keyMapper a mapping function to produce keys
 * @param valueMapper a mapping function to produce values
 * @param mergeFunction a merge function, used to resolve collisions between
 *                      values associated with the same key, as supplied
 *                      to {@link Map#merge(Object, Object, BiFunction)}
 * @param mapSupplier a function which returns a new, empty {@code Map} into
 *                    which the results will be inserted

例如:

HashMap<String, Object> src = ...;
TreeMap<String, Object> dest = src.entrySet().stream()
      .filter( ... )
      .collect(Collectors.toMap(Map.Entry::getKey , Map.Entry::getValue, (a,b) -> a, TreeMap::new));

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