add JsonExpressionUtils.java

sql/catalyst/src/main/java/org/apache/spark/sql/catalyst/expressions/json/JsonExpressionUtils.java

@@ -0,0 +1,60 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.spark.sql.catalyst.expressions.json;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+
+import com.fasterxml.jackson.core.JsonParser;
+import com.fasterxml.jackson.core.JsonToken;
+
+import org.apache.spark.sql.catalyst.expressions.SharedFactory;
+import org.apache.spark.sql.catalyst.json.CreateJacksonParser;
+import org.apache.spark.sql.catalyst.util.GenericArrayData;
+import org.apache.spark.unsafe.types.UTF8String;
+
+public class JsonExpressionUtils {
+
+  public static GenericArrayData jsonObjectKeys(UTF8String json) {
+    // return null for `NULL` input
+    if (json == null) {
+      return null;
+    }
+    try (JsonParser jsonParser =
+        CreateJacksonParser.utf8String(SharedFactory.jsonFactory(), json)) {
+      // return null if an empty string or any other valid JSON string is encountered
+      if (jsonParser.nextToken() == null || jsonParser.currentToken() != JsonToken.START_OBJECT) {
+        return null;
+      }
+      // Parse the JSON string to get all the keys of outermost JSON object
+      List<UTF8String> arrayBufferOfKeys = new ArrayList<>();
+
+      // traverse until the end of input and ensure it returns valid key
+      while (jsonParser.nextValue() != null && jsonParser.currentName() != null) {
+        // add current fieldName to the ArrayBuffer
+        arrayBufferOfKeys.add(UTF8String.fromString(jsonParser.currentName()));
+
+        // skip all the children of inner object or array
+        jsonParser.skipChildren();
+      }
+      return new GenericArrayData(arrayBufferOfKeys.toArray());
+    } catch (IOException e) {
+      return null;
+    }
+  }
+}