BAEL-5191-JsonNode-Get-All-Keys-From-A-Json-Structure (eugenp#11451)

* BAEL-5191-JsonNode-Get-All-Keys-From-A-Json-Structure

* Added test cases for GetAllKeysFromJSON class methods

* Updated test class name

jackson-modules/jackson/src/main/java/com/baeldung/jackson/jsonnode/GetAllKeysFromJSON.java

@@ -0,0 +1,172 @@
+package com.baeldung.jackson.jsonnode;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+
+import com.fasterxml.jackson.core.JsonFactory;
+import com.fasterxml.jackson.core.JsonParser;
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.core.JsonToken;
+import com.fasterxml.jackson.core.type.TypeReference;
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.node.ArrayNode;
+
+public class GetAllKeysFromJSON {
+
+    public static List<String> getKeysInJsonUsingMaps(String json, ObjectMapper mapper) {
+        List<String> keys = new ArrayList<>();
+
+        try {
+            Map<String, Object> jsonElements = mapper.readValue(json, new TypeReference<Map<String, Object>>() {
+            });
+            getAllKeys(jsonElements, keys);
+            return keys;
+
+        } catch (JsonProcessingException e) {
+            e.printStackTrace();
+        }
+
+        return keys;
+    }
+
+    public static void getAllKeys(Map<String, Object> jsonElements, List<String> keys) {
+
+        jsonElements.entrySet()
+            .forEach(entry -> {
+                keys.add(entry.getKey());
+                if (entry.getValue() instanceof Map) {
+                    Map<String, Object> map = (Map<String, Object>) entry.getValue();
+                    getAllKeys(map, keys);
+                } else if (entry.getValue() instanceof List) {
+                    List<?> list = (List<?>) entry.getValue();
+                    list.forEach(listEntry -> {
+                        if (listEntry instanceof Map) {
+                            Map<String, Object> map = (Map<String, Object>) listEntry;
+                            getAllKeys(map, keys);
+                        }
+                    });
+                }
+            });
+    }
+
+    public static List<String> getKeysInJsonUsingJsonNodeFieldNames(String json, ObjectMapper mapper) {
+        List<String> keys = new ArrayList<>();
+
+        try {
+            JsonNode jsonNode = mapper.readTree(json);
+            Iterator<String> iterator = jsonNode.fieldNames();
+            iterator.forEachRemaining(e -> keys.add(e));
+
+        } catch (JsonProcessingException e) {
+            e.printStackTrace();
+        }
+        return keys;
+    }
+
+    public static List<String> getAllKeysInJsonUsingJsonNodeFieldNames(String json, ObjectMapper mapper) {
+        List<String> keys = new ArrayList<>();
+
+        try {
+            JsonNode jsonNode = mapper.readTree(json);
+            getAllKeysUsingJsonNodeFieldNames(jsonNode, keys);
+
+        } catch (JsonProcessingException e) {
+            e.printStackTrace();
+        }
+        return keys;
+    }
+
+    public static List<String> getAllKeysInJsonUsingJsonNodeFields(String json, ObjectMapper mapper) {
+        List<String> keys = new ArrayList<>();
+
+        try {
+            JsonNode jsonNode = mapper.readTree(json);
+            getAllKeysUsingJsonNodeFields(jsonNode, keys);
+
+        } catch (JsonProcessingException e) {
+            e.printStackTrace();
+        }
+        return keys;
+    }
+
+    public static void getAllKeysUsingJsonNodeFields(JsonNode jsonNode, List<String> keys) {
+
+        if (jsonNode.isObject()) {
+            Iterator<Entry<String, JsonNode>> fields = jsonNode.fields();
+
+            fields.forEachRemaining(field -> {
+                keys.add(field.getKey());
+                getAllKeysUsingJsonNodeFieldNames((JsonNode) field.getValue(), keys);
+            });
+        } else if (jsonNode.isArray()) {
+            ArrayNode arrayField = (ArrayNode) jsonNode;
+            arrayField.forEach(node -> {
+                getAllKeysUsingJsonNodeFieldNames(node, keys);
+            });
+        }
+
+    }
+
+    public static void getAllKeysUsingJsonNodeFieldNames(JsonNode jsonNode, List<String> keys) {
+
+        if (jsonNode.isObject()) {
+            Iterator<String> fieldNames = jsonNode.fieldNames();
+
+            fieldNames.forEachRemaining(fieldName -> {
+                keys.add(fieldName);
+                getAllKeysUsingJsonNodeFieldNames(jsonNode.get(fieldName), keys);
+            });
+        } else if (jsonNode.isArray()) {
+            ArrayNode arrayField = (ArrayNode) jsonNode;
+            arrayField.forEach(node -> {
+                getAllKeysUsingJsonNodeFieldNames(node, keys);
+            });
+        }
+
+    }
+
+    public static List<String> getKeysInJsonUsingJsonParser(String json, ObjectMapper mapper) {
+        List<String> keys = new ArrayList<>();
+
+        try {
+            JsonNode jsonNode = mapper.readTree(json);
+            JsonParser jsonParser = jsonNode.traverse();
+            while (!jsonParser.isClosed()) {
+                if (jsonParser.nextToken() == JsonToken.FIELD_NAME) {
+                    keys.add((jsonParser.getCurrentName()));
+                }
+            }
+        } catch (JsonProcessingException e) {
+            e.printStackTrace();
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+
+        return keys;
+    }
+
+    public static List<String> getKeysInJsonUsingJsonParser(String json) {
+        List<String> keys = new ArrayList<>();
+
+        try {
+            JsonFactory factory = new JsonFactory();
+            JsonParser jsonParser = factory.createParser(json);
+            while (!jsonParser.isClosed()) {
+                if (jsonParser.nextToken() == JsonToken.FIELD_NAME) {
+                    keys.add((jsonParser.getCurrentName()));
+                }
+            }
+        } catch (JsonProcessingException e) {
+            e.printStackTrace();
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+
+        return keys;
+    }
+}

jackson-modules/jackson/src/test/java/com/baeldung/jackson/jsonnode/GetAllKeysFromJSONUnitTest.java

@@ -0,0 +1,56 @@
+package com.baeldung.jackson.jsonnode;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+
+public class GetAllKeysFromJSONUnitTest {
+
+    private static String json = "{\r\n" + "   \"Name\":\"Craig\",\r\n" + "   \"Age\":10,\r\n" + "   \"BookInterests\":[\r\n" + "      {\r\n" + "         \"Book\":\"The Kite Runner\",\r\n" + "         \"Author\":\"Khaled Hosseini\"\r\n" + "      },\r\n"
+        + "      {\r\n" + "         \"Book\":\"Harry Potter\",\r\n" + "         \"Author\":\"J. K. Rowling\"\r\n" + "      }\r\n" + "   ],\r\n" + "   \"FoodInterests\":{\r\n" + "      \"Breakfast\":[\r\n" + "         {\r\n"
+        + "            \"Bread\":\"Whole wheat\",\r\n" + "            \"Beverage\":\"Fruit juice\"\r\n" + "         },\r\n" + "         {\r\n" + "            \"Sandwich\":\"Vegetable Sandwich\",\r\n" + "            \"Beverage\":\"Coffee\"\r\n"
+        + "         }\r\n" + "      ]\r\n" + "   }\r\n" + "}";
+
+    private static ObjectMapper mapper = new ObjectMapper();
+
+    // Top level keys : [Name, Age, BookInterests, FoodInterests]
+    // All keys: [Name, Age, BookInterests, Book, Author, Book, Author, FoodInterests, Breakfast, Bread, Beverage, Sandwich, Beverage]
+
+    @Test
+    public void givenAJsonNode_whenUsingFieldNamesMethod_thenWeGetTopFieldNames() {
+        List<String> keys = GetAllKeysFromJSON.getKeysInJsonUsingJsonNodeFieldNames(json, mapper);
+        assertEquals(4, keys.size());
+    }
+
+    @Test
+    public void givenAJsonNode_whenUsingFieldNamesMethodForAllNodes_thenWeGetAllFieldNames() {
+        List<String> keys = GetAllKeysFromJSON.getAllKeysInJsonUsingJsonNodeFieldNames(json, mapper);
+        assertEquals(13, keys.size());
+    }
+
+    @Test
+    public void givenAJsonNode_whenUsingFieldsMethod_thenWeGetAllFieldNames() {
+        List<String> keys = GetAllKeysFromJSON.getAllKeysInJsonUsingJsonNodeFields(json, mapper);
+        assertEquals(13, keys.size());
+    }
+
+    @Test
+    public void givenAJsonNode_whenUsingJsonParserMethod_thenWeGetAllFieldNames() {
+        List<String> keys = GetAllKeysFromJSON.getKeysInJsonUsingJsonParser(json, mapper);
+        assertEquals(13, keys.size());
+
+        keys = GetAllKeysFromJSON.getKeysInJsonUsingJsonParser(json);
+        assertEquals(13, keys.size());
+    }
+
+    @Test
+    public void givenAJsonNode_whenUsingMaps_thenWeGetAllFieldNames() {
+        List<String> keys = GetAllKeysFromJSON.getKeysInJsonUsingMaps(json, mapper);
+        assertEquals(13, keys.size());
+    }
+
+}