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/pom.xml

@@ -108,6 +108,17 @@
                 </exclusion>
             </exclusions>
         </dependency>
+        <dependency>
+            <groupId>commons-io</groupId>
+            <artifactId>commons-io</artifactId>
+            <version>2.11.0</version>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter</artifactId>
+            <version>RELEASE</version>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 
     <build>

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();
+    }
+}

json-modules/json-2/src/test/java/com/baeldung/jsonvaluegetter/JSONObjectValueGetterUnitTest.java

@@ -0,0 +1,69 @@
+package com.baeldung.jsonvaluegetter;
+
+import org.apache.commons.io.IOUtils;
+import org.json.JSONArray;
+import org.json.JSONException;
+import org.json.JSONObject;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.List;
+
+public class JSONObjectValueGetterUnitTest {
+
+    private static JSONObject jsonObject;
+    private static JSONObjectValueGetter jsonObjectValueGetter = new JSONObjectValueGetter();
+
+    @BeforeAll
+    public static void loadJsonContent() throws IOException {
+        InputStream inputStream = JSONObjectValueGetterUnitTest.class.getClassLoader().getResourceAsStream("employee.json");
+        String jsonString = IOUtils.toString(inputStream, "UTF-8");
+        jsonObject = new JSONObject(jsonString);
+    }
+
+    @Test
+    public void getValueDirectly() {
+        JSONArray family = jsonObject.getJSONArray("family");
+        JSONObject sonObject = family.getJSONObject(1);
+        JSONObject sonData = sonObject.getJSONObject("son");
+        String sonName = sonData.getString("name");
+        Assertions.assertEquals(sonName, "Peter");
+    }
+
+    @Test
+    public void getAllAssociatedValuesRecursively() {
+        List<String> values = jsonObjectValueGetter.getValuesInObject(jsonObject, "son");
+        Assertions.assertEquals(values.size(), 1);
+
+        String sonString = values.get(0);
+        Assertions.assertTrue(sonString.contains("Peter"));
+        Assertions.assertTrue(sonString.contains("Schoolboy"));
+        Assertions.assertTrue(sonString.contains("11"));
+
+        values = jsonObjectValueGetter.getValuesInObject(jsonObject, "name");
+        Assertions.assertEquals(values.size(), 3);
+
+        Assertions.assertEquals(values.get(0), "Bob");
+        Assertions.assertEquals(values.get(1), "Alice");
+        Assertions.assertEquals(values.get(2), "Peter");
+    }
+
+    @Test
+    public void getNthValueRecursively() {
+        Assertions.assertEquals(jsonObjectValueGetter.getNthValue(jsonObject, "name", 1), "Bob");
+        Assertions.assertEquals(jsonObjectValueGetter.getNthValue(jsonObject, "name", 2), "Alice");
+        Assertions.assertEquals(jsonObjectValueGetter.getNthValue(jsonObject, "name", 3), "Peter");
+        Assertions.assertNull(jsonObjectValueGetter.getNthValue(jsonObject, "nonExistingKey", 1));
+    }
+
+    @Test
+    public void getCountRecursively() {
+        Assertions.assertEquals(jsonObjectValueGetter.getCount(jsonObject, "name"), 3);
+        Assertions.assertEquals(jsonObjectValueGetter.getCount(jsonObject, "age"), 3);
+        Assertions.assertEquals(jsonObjectValueGetter.getCount(jsonObject, "occupation"), 1);
+        Assertions.assertEquals(jsonObjectValueGetter.getCount(jsonObject, "nonExistingKey"), 0);
+    }
+}

json-modules/json-2/src/test/resources/employee.json

@@ -0,0 +1,30 @@
+{
+  "name" : "Bob",
+  "profession" : "Software engineer",
+  "department" : "Research",
+  "age" : 40,
+  "family" : [
+    {
+      "wife" : {
+        "name" : "Alice",
+        "profession" : "Doctor",
+        "age" : 38
+      }
+    },
+    {
+      "son" : {
+        "name" : "Peter",
+        "occupation" : "Schoolboy",
+        "age" : 11
+      }
+    }
+  ],
+  "performance" : [
+    {
+      "2020" : 4.5
+    },
+    {
+      "2021" : 4.8
+    }
+  ]
+}