用流解析列表，其中每个元素本身都是链接哈希图的列表

Question

我已经使用 JSON 路径解析了以下 JSON 字符串：

  {
   [
     [
        {
            "ID": "ExternalKey",
            "Name": "ExternalKey",
            "Label": "ExternalKey",
            "ExternalKey": "",
        "TranslatedName": "ExternalKey",
        "Type": "caption",
        "Self": "https://aqb629.saas.contentserv.com/admin/rest/product/Attribute/ExternalKey",
        "Value": "VSCHL01",
        "FormattedValue": "VSCHL01"
        },
        {
        "ID": "PdmarticleID",
        "Name": "PdmarticleID",
        "Label": "PdmarticleID",
        "ExternalKey": "",
        "TranslatedName": "PdmarticleID",
        "Type": "_id",
        "Self": "",
        "Value": 99942,
        "FormattedValue": 99942
        }
    ],
    [
        {
            "ID": "ExternalKey",
            "Name": "ExternalKey",
            "Label": "ExternalKey",
            "ExternalKey": "",
            "TranslatedName": "ExternalKey",
            "Type": "caption",
            "Self": "",
            "Value": "VSCHL02",
            "FormattedValue": "VSCHL02"
        },
        {
            "ID": "PdmarticleID",
            "Name": "PdmarticleID",
            "Label": "PdmarticleID",
            "ExternalKey": "",
            "TranslatedName": "PdmarticleID",
            "Type": "_id",
            "Self": "",
            "Value": 99944,
            "FormattedValue": 99944
        }
    ]
 ] 
}

我得到以下 Java 中的列表列表：

 List<List<LinkedHashMap<String,String>>> productsMasterMap = jsonContext.read(jsonPath);

我想通过流进行搜索，其中 ID = PdmArticleID 和 Value=99924 我可以得到以下结构

     [
        {
            "ID": "ExternalKey",
            "Name": "ExternalKey",
            "Label": "ExternalKey",
            "ExternalKey": "",
        "TranslatedName": "ExternalKey",
        "Type": "caption",
        "Self": "https://aqb629.saas.contentserv.com/admin/rest/product/Attribute/ExternalKey",
        "Value": "VSCHL01",
        "FormattedValue": "VSCHL01"
        },
        {
        "ID": "PdmarticleID",
        "Name": "PdmarticleID",
        "Label": "PdmarticleID",
        "ExternalKey": "",
        "TranslatedName": "PdmarticleID",
        "Type": "_id",
        "Self": "",
        "Value": 99942,
        "FormattedValue": 99942
        }
    ],

这是一个List>对象。我怎样才能做到这一点？我尝试过以下方法：

  List<LinkedHashMap> listOfMaps =    

  productsMasterMap.stream().filter(listOfHashMaps->
                  
  listOfHashMaps.stream().filter(m->m.get("ID").equals("PdmarticleID") &&   

  m.get("Value").equals("99945"))
                       
 .map(m->m).collect(Collectors.toList());

我想获取条件为真的内部列表元素。

Answer 1

您正在寻找 Stream.flatMap()

返回一个流，其中包含将此流的每个元素替换为映射流的内容的结果，该映射流是通过将提供的映射函数应用于每个元素而生成的。

List<List<LinkedHashMap<String,String>>> productsMasterMap = ...;

List<LinkedHashMap<String, String>> listOfMaps = productsMasterMap.stream()
  .flatMap(Collection::stream)
  .filter(element -> current filter condition)
  .toList();

作为旁注，我将使用自定义类，而不是

Map

，元素具有相同的属性。这将使代码更具可读性。

Answer 2

正如@Chaosfire提到的，你需要平面图。 对于您的情况，如果您需要内部列表元素作为过滤结果，则情况如下：

    String searchId = "PdmarticleID";
    Object searchValue = 99924;
    Optional<Map<String, Object>> result = productsMasterMap.stream()
            .flatMap(List::stream) // Flatten the nested lists
            .filter(map -> searchId.equals(map.get("ID")) && searchValue.equals(map.get("Value")))
            .findFirst();