Add isJson UDF

pinot-common/src/main/java/org/apache/pinot/common/function/scalar/StringFunctions.java

@@ -31,6 +31,7 @@
 import org.apache.commons.lang3.StringUtils;
 import org.apache.pinot.common.utils.RegexpPatternConverterUtils;
 import org.apache.pinot.spi.annotations.ScalarFunction;
+import org.apache.pinot.spi.utils.JsonUtils;
 
 
 /**
@@ -831,4 +832,24 @@ public static boolean like(String inputStr, String likePatternStr) {
     String regexPatternStr = RegexpPatternConverterUtils.likeToRegexpLike(likePatternStr);
     return regexpLike(inputStr, regexPatternStr);
   }
+
+  /**
+   * Checks whether the input string can be parsed into a json node or not. Useful for scenarios where we want
+   * to filter out malformed json. In case of nulls we return null itself, as null can be treated as valid json
+   * in partial-upsert scenarios. Upto the user to use null response accordingly.
+   *
+   * @param inputStr Input string to test for valid json
+   * @return in case of null value, it returns null. In case of non-null, it returns true in case of valid json
+   * parsing else false
+   *
+   */
+  @ScalarFunction(names = {"isJson", "is_json"})
+  public static boolean isJson(String inputStr) {
+    try {
+      JsonUtils.stringToJsonNode(inputStr);
+      return true;
+    } catch (Exception e) {
+      return false;
+    }
+  }
 }

pinot-common/src/test/java/org/apache/pinot/common/function/scalar/StringFunctionsTest.java

@@ -0,0 +1,43 @@
+/**
+ * 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.pinot.common.function.scalar;
+
+import org.testng.annotations.DataProvider;
+import org.testng.annotations.Test;
+
+import static org.testng.Assert.assertEquals;
+
+
+public class StringFunctionsTest {
+
+  @DataProvider(name = "isJson")
+  public static Object[][] isJsonTestCases() {
+    return new Object[][]{
+        {"", true},
+        {"{\"key\": \"value\"}", true},
+        {"{\"key\": \"value\", }", false},
+        {"{\"key\": \"va", false}
+    };
+  }
+
+  @Test(dataProvider = "isJson")
+  public void testIsJson(String input, boolean expectedValue) {
+    assertEquals(StringFunctions.isJson(input), expectedValue);
+  }
+}