在 JsonArray (javax.json.JsonArray) 中通过键或值查找 JsonObject 使用 Java 8 Lambas

Question

I haven't been able to find a concise/up-to-date answer on how to use Java 8 Lambdas to quickly locate a JsonObject in a JsonArray ( javax.json.JsonArray ). All the answers about loops, which are too verbose.

Suppose I have

JsonArray answersArray  = ...

The array is

[   {
        "activityQuestionId": "875",
        "questionType": "STARTTIME",
        "answer": "12:45am"
    }, {
        "activityQuestionId": "876",
        "questionType": "ENDTIME",
        "answer": "1:00am"
    }, 
    ...
    {
        "activityQuestionId": "SPECIAL",
        "questionType": "DROPDOWN",
        "answer": "756", 
        "extra": "SPECIAL/EXTRA"
    }
]

Normally, I can do

JsonArray answersArray  = ...
JsonObject obj1 = answersArray.getJsonObject(1); // This brings back 2nd object 
String str = obj1.getString("answer"); // This brings back 1:00am answer in 2nd object

I need to do the following:

• Find By Key: Locate JsonObject having the key "extra" . Only 1 object has it (the last), so that's the one I should get.
• Find By Value of Some Key: Locate JsonObject having "activityQuestionId": "SPECIAL" . The same last object should be returned.

JsonArray : https://docs.oracle.com/javaee/7/api/javax/json/JsonArray.html

Answer 1

Try this. This should work

 final Optional<Object> extra = IntStream.range(0, jsonArray.length())
                .mapToObj(i -> getJsonObject(jsonArray, i))
                .filter(Objects::nonNull)
                .map(this::getObject)
                .filter(Objects::nonNull)
                .findFirst();
     //if extra.isPresent() then do extra.get() to get the value
    }

   //Instead of returning a generic type try to return specific type
   //Better Exception handling
    private Object getObject(JSONObject entry) {
        try {
            return entry.get("extra");
        } catch (JSONException e) {
            e.printStackTrace();
        }
        return null;
    }

    private JSONObject getJsonObject(JSONArray jsonArray, int i) {
        try {
            return jsonArray.getJSONObject(i);
        } catch (JSONException e) {
            e.printStackTrace();
        }
        return null;
    }

This is not a complete solution. This should give you some idea about how to approach. You should check out how to handle exceptions inside lambdas if you want to use lamdas for this kinda code, because json processing throws lots of checked exceptions. And you cannot just throw those from inside lambdas, you need to handle it.

You need to think if using Streams is a good approach for this scenario or if its a over kill.

Answer 2

Locate JsonObject having key "extra"

JsonObject extraKeyJsonObject = value.stream()
        .map(JsonValue::asJsonObject)
        .filter(jo -> jo.containsKey("extra"))
        .findFirst()
        .orElse(null);// or something else

Locate JsonObject having "activityQuestionId": "SPECIAL"

JsonObject activityIdSpecialJsonObject = value.stream()
        .map(JsonValue::asJsonObject)
        .filter(jo -> "SPECIAL".equals(jo.getString("activityQuestionId", null)))
        .findFirst()
        .orElse(null);// or something else

Answer 3

Solution

List<JsonValue> objects1 = answersArray.stream().filter(obj -> 
            ((JsonObject)obj).getString("extra") != null).collect(Collectors.toList());

List<JsonValue> objects2 = answersArray.stream().filter(obj ->      
            "SPECIAL".equals(((JsonObject)obj).getString("activityQuestionId")).collect(Collectors.toList());

Answer 4

Try This...

JsonObject jsonObject= answersArray.getJsonObject(1) // 1 is the second index in the json array
String activityQuestionId= jsonObject.getString("activityQuestionId");
String questionType= jsonObject.getString("questionType");