使用 Java 8 Lambda 表达式将 String 数组转换为 Map [英] Convert String array to Map using Java 8 Lambda expressions

问题描述

是否有更好的函数方式使用 Java 8 lambda 语法将key:value"形式的字符串数组转换为 Map?

Is there a better functional way of converting an array of Strings in the form of "key:value" to a Map using the Java 8 lambda syntax?

Arrays.asList("a:1.0", "b:2.0", "c:3.0")
        .stream()
        .map(elem -> elem.split(":")
        .collect(Collectors.toMap(keyMapper?, valueMapper?));

我现在的解决方案似乎并不实用:

The solution I have right now does not seem really functional:

Map<String, Double> kvs = new HashMap<>();
Arrays.asList("a:1.0", "b:2.0", "c:3.0")
        .stream()
        .map(elem -> elem.split(":"))
        .forEach(elem -> kvs.put(elem[0], Double.parseDouble(elem[1])));

推荐答案

您可以修改您的解决方案以将 String 数组的 Stream 收集到 Map(而不是使用 forEach):

You can modify your solution to collect the Stream of String arrays into a Map (instead of using forEach) :

Map<String, Double> kvs =
    Arrays.asList("a:1.0", "b:2.0", "c:3.0")
        .stream()
        .map(elem -> elem.split(":"))
        .collect(Collectors.toMap(e -> e[0], e -> Double.parseDouble(e[1])));

当然，这个解决方案没有针对无效输入的保护.也许您应该添加一个过滤器，以防拆分字符串没有分隔符:

Of course this solution has no protection against invalid input. Perhaps you should add a filter just in case the split String has no separator :

Map<String, Double> kvs =
    Arrays.asList("a:1.0", "b:2.0", "c:3.0")
        .stream()
        .map(elem -> elem.split(":"))
        .filter(elem -> elem.length==2)
        .collect(Collectors.toMap(e -> e[0], e -> Double.parseDouble(e[1])));

这仍然不能保护您免受所有无效输入的侵害(例如，"c:3r" 会导致 parseDouble 抛出 NumberFormatException>).

This still doesn't protect you against all invalid inputs (for example "c:3r" would cause NumberFormatException to be thrown by parseDouble).

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