Github user markap14 commented on a diff in the pull request:
https://github.com/apache/nifi/pull/303#discussion_r64234770
--- Diff:
nifi-commons/nifi-expression-language/src/main/java/org/apache/nifi/attribute/expression/language/evaluation/functions/JsonPathEvaluator.java
---
@@ -0,0 +1,98 @@
+/*
+ * 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 java.util.List;
+import java.util.Map;
+import java.util.Objects;
+
+import org.apache.nifi.attribute.expression.language.evaluation.Evaluator;
+import
org.apache.nifi.attribute.expression.language.evaluation.QueryResult;
+import
org.apache.nifi.attribute.expression.language.evaluation.StringEvaluator;
+import
org.apache.nifi.attribute.expression.language.evaluation.StringQueryResult;
+
+import com.jayway.jsonpath.Configuration;
+import com.jayway.jsonpath.DocumentContext;
+import com.jayway.jsonpath.InvalidJsonException;
+import com.jayway.jsonpath.JsonPath;
+import com.jayway.jsonpath.spi.json.JacksonJsonProvider;
+import com.jayway.jsonpath.spi.json.JsonProvider;
+
+
+public class JsonPathEvaluator extends StringEvaluator {
+
+ private static final StringQueryResult NULL_RESULT = new
StringQueryResult("");
+ private static final Configuration STRICT_PROVIDER_CONFIGURATION =
Configuration.builder().jsonProvider(new JacksonJsonProvider()).build();
+ private static final JsonProvider JSON_PROVIDER =
STRICT_PROVIDER_CONFIGURATION.jsonProvider();
+
+ private final Evaluator<String> subject;
+ private final Evaluator<String> jsonPathExp;
+
+ public JsonPathEvaluator(final Evaluator<String> subject, final
Evaluator<String> jsonPathExp) {
+ this.subject = subject;
+ this.jsonPathExp = jsonPathExp;
+ }
+
+ @Override
+ public QueryResult<String> evaluate(final Map<String, String>
attributes) {
+ final String subjectValue =
subject.evaluate(attributes).getValue();
+ if (subjectValue == null || subjectValue.length() == 0) {
+ return NULL_RESULT;
+ }
+ DocumentContext documentContext = null;
+ try {
+ documentContext =
validateAndEstablishJsonContext(subjectValue);
+ } catch (InvalidJsonException e) {
+ return NULL_RESULT;
+ }
+
+ final JsonPath compiledJsonPath =
JsonPath.compile(jsonPathExp.evaluate(attributes).getValue());
--- End diff --
In the vast majority of use cases, I would expect that the JSON Path will
be a literal string that does not reference any attributes. In this case, I
would want to avoid compiling the JSON Path every time. Would recommend that if
the jsonPathExp is an instance of the StringLiteralEvaluator, we pre-compile
the JSON Path. We follow a similar pattern with the MatchesEvaluator for
pre-compiling regular expressions, and it can make a pretty huge difference on
performance.
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