[GitHub] [nifi] MikeThomsen commented on a diff in pull request #6574: [NIFI-10612] Initial check in of isJson code.

[GitBox <gi...@apache.org>]

MikeThomsen commented on code in PR #6574:
URL: https://github.com/apache/nifi/pull/6574#discussion_r1004660449


##########
nifi-commons/nifi-expression-language/src/main/java/org/apache/nifi/attribute/expression/language/evaluation/functions/IsJsonEvaluator.java:
##########
@@ -0,0 +1,56 @@
+/*
+ * 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.nifi.attribute.expression.language.evaluation.functions;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import org.apache.commons.lang3.StringUtils;
+import org.apache.nifi.attribute.expression.language.EvaluationContext;
+import org.apache.nifi.attribute.expression.language.evaluation.BooleanEvaluator;
+import org.apache.nifi.attribute.expression.language.evaluation.BooleanQueryResult;
+import org.apache.nifi.attribute.expression.language.evaluation.Evaluator;
+import org.apache.nifi.attribute.expression.language.evaluation.QueryResult;
+
+import java.io.IOException;
+
+public class IsJsonEvaluator extends BooleanEvaluator {
+    private static final ObjectMapper MAPPER = new ObjectMapper();
+    private final Evaluator<String> subject;
+
+    public IsJsonEvaluator(Evaluator<String> subject) {
+        this.subject = subject;
+    }
+
+    @Override
+    public QueryResult<Boolean> evaluate(EvaluationContext evaluationContext) {
+        final String subjectValue = subject.evaluate(evaluationContext).getValue();

Review Comment:
   You should consider checking the first and last characters for opening and closing JSON blocks (array and object open/close) so that you can short circuit the evaluation of strings which don't even superficially resemble JSON. While literals can technically be valid JSON, I'm not sure if the trade off is worth it.



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