如何在Collectors.toMap合并函数中获取密钥？ [英] How to get the key in Collectors.toMap merge function?

问题描述

在 Collectors.toMap（）期间找到重复的键条目时，合并函数（o1，o2）被叫。

When a duplicate key entry is found during Collectors.toMap(), the merge function (o1, o2) is called.

问题：如何获得导致重复的密钥？

Question: how can I get the key that caused the duplication?

String keyvalp = "test=one\ntest2=two\ntest2=three";

Pattern.compile("\n")
    .splitAsStream(keyval)
    .map(entry -> entry.split("="))
    .collect(Collectors.toMap(
        split -> split[0],
        split -> split[1],
        (o1, o2) -> {
            //TODO how to access the key that caused the duplicate? o1 and o2 are the values only
            //split[0]; //which is the key, cannot be accessed here
        },
    HashMap::new));

在合并功能中，我想根据键决定我取消映射，或继续并接受这些值。

Inside the merge function I want to decide based on the key which if I cancel the mapping, or continue and take on of those values.

推荐答案

您需要使用自定义收集器或使用不同的方法。

You need to use a custom collector or use a different approach.

Map<String, String> map = new Hashmap<>();
Pattern.compile("\n")
    .splitAsStream(keyval)
    .map(entry -> entry.split("="))
    .forEach(arr -> map.merge(arr[0], arr[1], (o1, o2) -> /* use arr[0]));

编写自定义收集器相当复杂。你需要一个TriConsumer（键和两个值）是类似的，它不在JDK中，这就是为什么我很确定没有使用的内置函数。 ;）

Writing a custom collector is rather more complicated. You need a TriConsumer (key and two values) is similar which is not in the JDK which is why I am pretty sure there is no built in function which uses. ;)

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