How to Get All Keys from a Json-Object as a String Array in Java

How to get all keys from a JSON-Object as a String array in Java

JSONObject implements the Map interface, so you can use the same way you'd use for Map to generate the list of keys. In particular, you can use the .keySet() or .entrySet() method.

For example (adapted from here):

JSONObject jsonObj = ...;
List<String> l = new ArrayList<String>(jsonObj.keySet());

Java - Extract the keys from JSON object in to a string whose values are true

The trick is walking the JSON tree and examining each node to determine if it is a BooleanNode or not.

This code will produce a List of node names that are of BooleanNode type AND have a true value:

    @Test
    public void test4() throws JsonProcessingException, IOException {
        // https://stackoverflow.com/questions/69224118/java-extract-the-keys-from-json-object-in-to-a-string-whose-values-are-true
        final ObjectMapper mapper = new ObjectMapper();
        final InputStream jsonStream = getClass().getClassLoader().getResourceAsStream("test4.json");
        final JsonNode root = mapper.readTree(jsonStream);
        final List<String> nodes = new ArrayList<>();
        walkJsonTree("root", root, nodes);
        System.out.println(nodes);
    }

    private void walkJsonTree(final String name, final JsonNode node, final List<String> trueNodes) {
        if (node.isObject()) {
            final ObjectNode n = (ObjectNode) node;
            final Iterator<String> it = n.fieldNames();
            while (it.hasNext()) {
                final String fn = it.next();
                walkJsonTree(fn, n.get(fn), trueNodes);
            }
        } else if (node.isArray()) {
            final ArrayNode n = (ArrayNode) node;
            final Iterator<JsonNode> it = n.iterator();
            while (it.hasNext()) {
                walkJsonTree("array", it.next(), trueNodes);
            }
        } else if (node.isBoolean()) {
            final BooleanNode n = (BooleanNode) node;
            if (n.booleanValue()) {
                trueNodes.add(name);
            }
        }
    }

Get child key and values from JSON array: Java

Your problem is not related to Java, you just forgot a step.

String currentParentKeyProperties =
fieldsObject.optString(currentParentKey);

is not correct, what you want is to get a JSONObject.

How to get values of keys of inside array in json array

The problem is in this statement bindings is a JsonArray, get it as JsonArray directly

JsonArray array = entry.getValue().getAsJsonObject().getAsJsonArray("bindings");

Solution

for(Map.Entry<String, JsonElement> entry : results.entrySet()) {
        JsonArray array = entry.getValue().getAsJsonArray();
        for (JsonElement jsonElement : array) {
             for (Map.Entry<String, JsonElement> entry1 : jsonElement.getAsJsonObject().entrySet()) {
                 System.out.println("Key = " + entry1.getKey() + " Value = " + entry1.getValue() );
            }
        }

Extracting Keys from a JSONObject using keySet()

The javadoc says:

public interface JsonObject
extends JsonStructure, Map<String,JsonValue>

So, a JSONObject is a Map whose keys are of type String, and whose values are of type JSONValue.

And the javadoc of Map<K, V>.keySet() says:

Set<K> keySet()

Returns a Set view of the keys contained in this map

So, what JSONObject.keySet() returns is a Set<String> (which is quite logical, since keys of JSON objects are strings).

So all that you want is:

Set<String> keys = posts.keySet();

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