Using streams to extract specific entries of a List of Maps in to a new Map-CodePudding

Given a org.bson.Document

{  
  "doneDate":"",
  "todoEstimates":"",
  "forecastDate":"",
  "cardType":{
    "projectData":[
      {
        "color":"#ffcd03",
        "boardId":"30022"
      },
      {
        "color":"#ffcd03",
        "boardId":"1559427"
      }
    ],
    "cardFields":[
      {
        "fieldName":"id",
        "fieldLabel":"Unique ID",
        "fieldType":"Integer",
        "itemType":"Long",
        "isRequired":"NO",
        "isReadOnly":"Yes",
        "isDisabled":"NO",
        "inputMethod":"System Generated",
        "defaultValue":null,
        "isUserType":"No"
      },
      {
        "fieldName":"name",
        "fieldLabel":"Title",
        "fieldType":"Single-Line Text",
        "itemType":"String",
        "isRequired":"Yes",
        "isReadOnly":"NO",
        "isDisabled":"NO",
        "inputMethod":"Manual Entry",
        "defaultValue":null,
        "isUserType":"No"
       }
    ]
}

How do I extract the values of fieldName and fieldLabel via streams into the following?

{
   "id": "Unique ID",
   "name:" "Title",
   ...
}

I tried the following but I get stuck at the part where I get value of the cardFields list.

document.entrySet().stream().filter(e -> e.getKey().equals("cardType"))
.collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue))
.entrySet().stream().filter(e -> e.getKey().equals("cardFields"))
        .map(e -> (Map)e.getValue()).toList();

CodePudding user response：

Here is a working solution with streams:

Map<String, Object> fields = ((List<Map<String, Object>>) ((Map<String, Object>) document.entrySet()
            .stream()
            .filter(entry -> entry.getKey().equals("cardType"))
            .findFirst()
            .orElseThrow(() -> new RuntimeException("card type not found"))
            .getValue())
            .entrySet()
            .stream()
            .filter(entry -> entry.getKey().equals("cardFields"))
            .findFirst()
            .orElseThrow(() -> new RuntimeException("card fields not found"))
            .getValue())
            .stream()
            .collect(Collectors.toMap(el -> el.get("fieldName").toString(), element -> element.get("fieldLabel")));
Document result = new Document(fields);
System.out.println(result.toJson());

That's probably the worst code i have written - absolutely unreadable and you can't debug it. I would suggest that you do not use stream for this particular task, it isn't the right tool for it. So here is another working solution using Map.get(key):

Map<String, Object> cardType = (Map<String, Object>) document.get("cardType");
List<Map<String, Object>> cardFields = (List<Map<String, Object>>) cardType.get("cardFields");
Document result = new Document();
cardFields.forEach(cardField -> result.put((String) cardField.get("fieldName"), cardField.get("fieldLabel")));
System.out.println(result.toJson());

This is shorter, readable, you can debug it if needed and probably it's more performant. I'd say it's much better overall.

CodePudding user response：

You may be able to parse your document like this:

Document cardType = document.get("cardType", Document.class);
final Class<? extends List> listOfMaps = new ArrayList<Map<String, String>>().getClass();
List<Map<String, String>> fields = cardType.get("cardFields", listOfMaps);
fields.stream().map(f -> {
    System.out.println(f.get("fieldName")   ": "   f.get("fieldLabel"));
    // here you can construct your new object
}).collect(Collectors.toList());

CodePudding user response：

If you don't mind casting a lot, you could try following:

    List cardFields = (List) ((Map) document.get("cardType")).get("cardFields");

    Map<String, String> map = (Map) cardFields.stream()
            .collect(Collectors.toMap(cf -> ((Document) cf).getString("fieldName"),
                    cv -> ((Document) cv).getString("fieldLabel")));
    
    System.out.println(map);

or you can emit omit the casting with the following:

    List<Document> carFields = document.get("cardType", Document.class)
                                       .getList("cardFields", Document.class);
    Map<String, String> map = carFields.stream()
            .collect(Collectors.toMap(k -> k.getString("fieldName"), 
                                      v -> v.getString("fieldLabel")));
    System.out.println(map);