I have task with JSONObject, and exactly two JSONArray to retrieve some key and value values and return them as JSONArray:

the first JSONArray consists of two objects as below:

[{"name": "John", "id": "1"}, {"name": "Adam", "id": "2"}]

the second JSONArray consists of three objects (the one with id = 3 is omitted), where "id" is a link between two JSONArray:

[{"color:" red "," id ":" 1 "," country ":" Poland "}, {" color ":" green "," id ":" 2 "," country ":" Germany " }, {"color:" red "," id ":" 3 "," country ":" England "}]

and finally I would like to get JSONArray where we have two JSONObjects:

[{"color:" red "," name ":" John "," country ":" Poland "}, {" color ":" green "," name ":" Adam "," country ":" Germany " }]

Have any of you ever done similar things and would be able to get a tip?

Regards, Stan

Actually I tried create new JSONObject and next add to JSON Array, but I don't know how get only two JSONObject from second JSONArray and finally get expected result JSONArray.

CodePudding user response：

Assuming you are using the org.json classes JSONObject and JSONArray, something like this should work:

NOTE: it will only accept one value per key in the merged objects, if you want to merge values for the same key or pick a certain value for a key (if multiple exist) based on certain criteria, you will need additional logic

    JSONArray[] arraysToMerge = // array of your json arrays to merge on 'id'
    Map<String, JSONObject> merged = new HashMap<>();
    for (JSONArray array : arraysToMerge) {
      for (int i = 0; i < array.length(); i  ) {
        JSONObject obj = array.optJSONObject(i);
        if (obj != null) {
          String id = obj.optString("id");
          if (id != null) {
            JSONObject existingObj = merged.computeIfAbsent(id, (k) -> {
              obj.remove("id");
              return obj;
            });
            for (String name : JSONObject.getNames(obj)) {
              if (!name.equals("id")) {
                existingObj.put(name, obj.get(name));
              }
            }
          }
        }
      }
    }
    JSONArray mergedArray = new JSONArray(merged.values());

CodePudding user response：

Library Josson & Jossons has join operation.

https://github.com/octomix/josson

// Deserialization
Jossons jossons = new Jossons();
jossons.putDataset("array1",
    Josson.fromJsonString(
        "[{\"name\": \"John\", \"id\": \"1\"},"  
        " {\"name\": \"Adam\", \"id\": \"2\"}]"));
jossons.putDataset("array2",
    Josson.fromJsonString(
        "[{\"color\": \"red\", \"id\": \"1\", \"country\": \"Poland\"},"  
        " {\"color\": \"green\", \"id\": \"2\", \"country\": \"Germany\"},"  
        " {\"color\": \"red\", \"id\": \"3\", \"country\": \"England\"}]"));
// Left join
JsonNode node = jossons.evaluateQuery("array1{id} <=< array2{id}");
// Output
System.out.println(node.toPrettyString());
// Remove "id"
System.out.println(Josson.create(node).getNode("field(id:)").toPrettyString());

Output

[ {
  "name" : "John",
  "id" : "1",
  "color" : "red",
  "country" : "Poland"
}, {
  "name" : "Adam",
  "id" : "2",
  "color" : "green",
  "country" : "Germany"
} ]

Output after removed "id"

[ {
  "name" : "John",
  "color" : "red",
  "country" : "Poland"
}, {
  "name" : "Adam",
  "color" : "green",
  "country" : "Germany"
} ]