Add code for BAEL-5878: Getting a Value in JSONObject (#13157)

* BAEL-5878: Getting a Value in JSONObject. Add JsonObjectValueGetter with unit tests

* Move json-value-getter under json-2 module

* Update packages for the source and unit test files

* Rename test class, move employee.json under test/resources

Co-authored-by: Rafael Engibaryan <rafael.engibaryan.1@gmail.com>

json-modules/json-2/src/main/java/com/baeldung/jsonvaluegetter/JSONObjectValueGetter.java

@@ -0,0 +1,87 @@
+package com.baeldung.jsonvaluegetter;
+
+import org.json.JSONArray;
+import org.json.JSONObject;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class JSONObjectValueGetter {
+
+    /**
+     * Get values associated with the provided key in the given JSONObject instance
+     *
+     * @param jsonObject JSONObject instance in which to search the key
+     * @param key        Key we're interested in
+     *
+     * @return List of values associated with the given key, in the order of appearance.
+     *         If the key is absent, empty list is returned.
+     */
+    public List<String> getValuesInObject(JSONObject jsonObject, String key) {
+        List<String> accumulatedValues = new ArrayList<>();
+        for (String currentKey : jsonObject.keySet()) {
+            Object value = jsonObject.get(currentKey);
+            if (currentKey.equals(key)) {
+                accumulatedValues.add(value.toString());
+            }
+
+            if (value instanceof JSONObject) {
+                accumulatedValues.addAll(getValuesInObject((JSONObject)value, key));
+            } else if (value instanceof JSONArray) {
+                accumulatedValues.addAll(getValuesInArray((JSONArray)value, key));
+            }
+        }
+
+        return accumulatedValues;
+    }
+
+    /**
+     * Get values associated with the provided key in the given JSONArray instance
+     *
+     * @param jsonArray JSONArray instance in which to search the key
+     * @param key       Key we're interested in
+     *
+     * @return List of values associated with the given key, in the order of appearance.
+     *         If the key is absent, empty list is returned.
+     */
+    public List<String> getValuesInArray(JSONArray jsonArray, String key) {
+        List<String> accumulatedValues = new ArrayList<>();
+        for (Object obj : jsonArray) {
+            if (obj instanceof JSONArray) {
+                accumulatedValues.addAll(getValuesInArray((JSONArray)obj, key));
+            } else if (obj instanceof JSONObject) {
+                accumulatedValues.addAll(getValuesInObject((JSONObject)obj, key));
+            }
+        }
+
+        return accumulatedValues;
+    }
+
+    /**
+     * Among all the values associated with the given key, get the N-th value
+     *
+     * @param jsonObject JSONObject instance in which to search the key
+     * @param key        Key we're interested in
+     * @param N          Index of the value to get
+     *
+     * @return N-th value associated with the key, or null if the key is absent or
+     *         the number of values associated with the key is less than N
+     */
+    public String getNthValue(JSONObject jsonObject, String key, int N) {
+        List<String> values = getValuesInObject(jsonObject, key);
+        return (values.size() >= N) ? values.get(N - 1) : null;
+    }
+
+    /**
+     * Count the number of values associated with the given key
+     *
+     * @param jsonObject JSONObject instance in which to count the key
+     * @param key        Key we're interested in
+     *
+     * @return The number of values associated with the given key
+     */
+    public int getCount(JSONObject jsonObject, String key) {
+        List<String> values = getValuesInObject(jsonObject, key);
+        return values.size();
+    }
+}