Collectors.toMap具有相同的键（打印相同的键）

问题描述

我有这个代码来获取地图：

I have this code to get map:

List<MyObject> myList = myMethod.getList();
myList.stream().collect(
    Collectors.toMap(
        MyObject::getKey,
        MyObject::getValue,
        (e1, e2) -> {
            System.out.println("Duplicate keys !!!");
            return e1;
        },
        LinkedHashMap::new
    )
);

如何使用重复键打印重复密钥消息？

how i can print message "Duplicate keys" with duplicate key?

推荐答案

使用当前代码，您将收到消息Duplicate keys，其中包含 MyObject 列表，其中包含至少2个 MyObject 具有与 getKey（）的值相等的对象，例如 Arrays.asList（new MyObject（foo，bar），新的MyObject（foo，bar2））。

With your current code, you will get the message "Duplicate keys" with a list of MyObject which contains at least 2 instances of MyObject that have equal objects as value for getKey(), for example Arrays.asList(new MyObject("foo", "bar"), new MyObject("foo", "bar2")).

到目前为止，无法获得相应的密钥，您目前获得的密钥来自merge函数的实际上是2个值，这些值使用相同的键映射，需要合并以保留相应键的一个值。

Up to now it is not possible to get the corresponding key, what you currently get from the merge function are actually 2 values mapped with the same key that need to be merged to keep only one value for the corresponding key.

您的问题已在 Java 9 中修复，请参阅了解更多详细信息，相应的修复将允许我们从合并功能获取密钥和要合并的值。

Your problem is a known issue that is fixed in Java 9 see JDK-8040892 for more details, the corresponding fix will allow us to get from the merge function both the key and the values to merge.

另见

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