Java Stream：如何从JSON中查找id？

huangapple
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英文:

Java Stream: How to find id from json?

问题

我有一个以下的 JSON，以及一个与之类似的类 MyClient：

  1. [
  2.     {
  3.         "id": 2,
  4.         "partners": [
  5.             {
  6.                 "configuration": {
  7.                     "connect-fleet-sync": false
  8.                 },
  9.                 "id": "cf89cbc5-0886-48cc-81e7-ca6123bc4857"
  10.             },
  11.             {
  12.                 "configuration": {
  13.                     "connect-fleet-sync": false
  14.                 },
  15.                 "id": "cf89cbc5-0886-48cc-81e7-ca6123bc4967"
  16.             }
  17.         ]
  18.     },
  19.     {
  20.         "id": 3,
  21.         "partners": [
  22.             {
  23.                 "configuration": {
  24.                     "connect-fleet-sync": false
  25.                 },
  26.                 "id": "c3354af5-16e3-4713-b1f5-a5369c0b13d6"
  27.             }
  28.         ]
  29.     }
  30. ]

我需要一个方法，它接收 UUID，然后返回 id。

例如 findClientId("cf89cbc5-0886-48cc-81e7-ca6123bc4967")，然后返回 2：

以下是我尝试过的代码：

  1. public static void findClientId(String partnerId, MyClient[] allMyClients) {
  2.     Stream.of(allMyClients)
  3.         .map(MyClient::getPartners)
  4.         .forEach(partners ->
  5.             partners.stream()
  6.                 .filter(partner -> partner.getId().equals(partnerId))
  7.                 .map(Partner::getClientId)
  8.                 .forEach(System.out::println)
  9.         );
  10. }

但是它报错 Non-static method cannot be referenced from a static context，在 .forEach(Partner::getPartnerId) 这一行。

英文:

I have a json as below and a similar classes respect to it MyClient:

  1. [
  2.     {
  3.         "id": 2,
  4.         "partners": [
  5.             {
  6.                 "configuration": {
  7.                     "connect-fleet-sync": false
  8.                 },
  9.                 "id": "cf89cbc5-0886-48cc-81e7-ca6123bc4857"
  10.             },
  11.             {
  12.                 "configuration": {
  13.                     "connect-fleet-sync": false
  14.                 },
  15.                 "id": "cf89cbc5-0886-48cc-81e7-ca6123bc4967"
  16.             }
  17.         ]
  18.     },
  19.     {
  20.         "id": 3,
  21.         "partners": [
  22.             {
  23.                 "configuration": {
  24.                     "connect-fleet-sync": false
  25.                 },
  26.                 "id": "c3354af5-16e3-4713-b1f5-a5369c0b13d6"
  27.             }
  28.         ]
  29.     }
  30. ]

I need a method which receives the uuid and it returns id.

Fr example findClientId("cf89cbc5-0886-48cc-81e7-ca6123bc4967") and then it returns 2:

Here is what i have tried:

  1.   public static void findClientId(String partnerId, MyClient[] allMyClients) {
  2.     Stream.of(allMyClients)
  3.         .map(MyClient::getPartners)
  4.         .forEach(Partner::getPartnerId)
  5.         .filter(
  6.             partner ->partner.id.equals(partnerId)))
  7.     .map(MyClient::getId);
  8.   }

But it complains Non-static method cannot be referenced from a static context
in the line .forEach(Partner::getPartnerId)

答案1

得分: 2

首先，Stream.forEach 是void类型。在它之后无法调用.filter或任何其他方法。除此之外，.map(MyClient::getPartners) 会使你在流水线中丢失 MyClient 的信息，而你实际上想要的是 MyClient.getId。你需要在每个客户端的合作伙伴列表上使用嵌套流进行过滤。

你的代码应该是：

  1. public static String findClientId(String partnerId, MyClient[] allMyClients) {
  2.     return Stream.of(allMyClients)
  3.             .filter(client -> client.getPartners()
  4.                     .stream()
  5.                     .anyMatch(partner -> partner.getPartnerId().equals(partnerId)))
  6.             .map(MyClient::getId)
  7.             .findAny()
  8.             .orElse(null); // 根据需要更改
  9. }
英文:

First, Stream.forEach is void. You can't invoke .filter or any other method after it. Beside that, .map(MyClient::getPartners) would make you lose MyClient information in the pipeline while it's MyClient.getId that you want. You'd have to use a nested stream to for filtering on partner list in each client.

Your code should be:

  1. public static String findClientId(String partnerId, MyClient[] allMyClients) {
  2. 	return Stream.of(allMyClients)
  3. 			.filter(client -> client.getPartners()
  4. 					.stream()
  5. 					.anyMatch(partner -> partner.getPartnerId().equals(partnerId)))
  6. 			.map(MyClient::getId)
  7. 			.findAny()
  8. 			.orElse(null); // change to whatever is desired
  9. }

huangapple
  • 本文由 发表于 2020年10月20日 10:21:09
  • 转载请务必保留本文链接：https://go.coder-hub.com/64437573.html
  • java
  • java-8
  • java-stream
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