如何转换Map< String，String>列出< String>使用谷歌收藏 [英] how to transform Map<String,String> to List<String> using google collections

问题描述

我有一个包含字符串的地图，我想将其转换为一个字符串列表，其中作为键值分隔符。是否可以使用谷歌收藏？

I have a map with strings, I want to transform it to a list of strings with " " as a key value separator. Is it possible using google collections?

我想用谷歌收藏品做的代码示例：

Code example that I want to do using google collections:

public static List<String> addLstOfSetEnvVariables(Map<String, String> env)
{
    ArrayList<String> result = Lists.newArrayList();
    for (Entry<String, String> entry : env.entrySet())
    {
        result.add(entry.getKey() + " " + entry.getValue());
    }
    return result;
}

推荐答案

在这里：

private static final Joiner JOINER = Joiner.on(' ');
public List<String> mapToList(final Map<String, String> input){
    return Lists.newArrayList(
        Iterables.transform(
            input.entrySet(), new Function<Map.Entry<String, String>, String>(){
                @Override
                public String apply(final Map.Entry<String, String> input){
                    return JOINER.join(input.getKey(), input.getValue());
                }
            }));
}

更新：优化代码。使用Joiner常量应该比String.concat（）快得多

Update: optimized code. Using a Joiner constant should be much faster than String.concat()

这些天，我当然会这样做Java 8流。不需要外部库。

These days, I would of course do this with Java 8 streams. No external lib needed.

public List<String> mapToList(final Map<String, String> input) {
    return input.entrySet()
                .stream()
                .map(e -> new StringBuilder(
                             e.getKey().length()
                                     + e.getValue().length()
                                     + 1
                     ).append(e.getKey())
                      .append(' ')
                      .append(e.getValue())
                      .toString()
                )
                .collect(Collectors.toList());
}

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