NIFI-12121 Added Transform Result Filter to JSLTTransformJSON

This closes #7922

Signed-off-by: David Handermann <exceptionfactory@apache.org>

nifi-nar-bundles/nifi-jslt-bundle/nifi-jslt-processors/src/main/java/org/apache/nifi/processors/jslt/JSLTTransformJSON.java

@@ -62,6 +62,7 @@ import java.io.BufferedReader;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.InputStreamReader;
+import java.io.StringReader;
 import java.io.UncheckedIOException;
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -87,6 +88,8 @@ import static org.apache.nifi.processors.jslt.JSLTTransformJSON.TransformationSt
         + "fails, the original FlowFile is routed to the 'failure' relationship.")
 public class JSLTTransformJSON extends AbstractProcessor {
 
+    public static String JSLT_FILTER_DEFAULT = ". != null and . != {} and . != []";
+
     public static final PropertyDescriptor JSLT_TRANSFORM = new PropertyDescriptor.Builder()
             .name("jslt-transform-transformation")
             .displayName("JSLT Transformation")
@@ -127,6 +130,18 @@ public class JSLTTransformJSON extends AbstractProcessor {
             .required(true)
             .build();
 
+    public static final PropertyDescriptor RESULT_FILTER = new PropertyDescriptor.Builder()
+            .name("jslt-transform-result-filter")
+            .displayName("Transform Result Filter")
+            .description("A filter for output JSON results using a JSLT expression. This property supports changing the default filter,"
+                    + " which removes JSON objects with null values, empty objects and empty arrays from the output JSON."
+                    + " This JSLT must return true for each JSON object to be included and false for each object to be removed."
+                    + " Using a filter value of \"true\" to disables filtering.")
+            .addValidator(StandardValidators.NON_EMPTY_VALIDATOR)
+            .required(true)
+            .defaultValue(JSLT_FILTER_DEFAULT)
+            .build();
+
     public static final Relationship REL_SUCCESS = new Relationship.Builder()
             .name("success")
             .description("The FlowFile with transformed content will be routed to this relationship")
@@ -146,7 +161,8 @@ public class JSLTTransformJSON extends AbstractProcessor {
                         JSLT_TRANSFORM,
                         TRANSFORMATION_STRATEGY,
                         PRETTY_PRINT,
-                        TRANSFORM_CACHE_SIZE
+                        TRANSFORM_CACHE_SIZE,
+                        RESULT_FILTER
                 )
         );
 
@@ -174,26 +190,33 @@ public class JSLTTransformJSON extends AbstractProcessor {
     protected Collection<ValidationResult> customValidate(ValidationContext validationContext) {
         final List<ValidationResult> results = new ArrayList<>(super.customValidate(validationContext));
 
-        final ValidationResult.Builder transformBuilder = new ValidationResult.Builder().subject(JSLT_TRANSFORM.getDisplayName());
-
         final PropertyValue transformProperty = validationContext.getProperty(JSLT_TRANSFORM);
         if (transformProperty.isExpressionLanguagePresent()) {
-            transformBuilder.valid(true);
+            final ValidationResult.Builder transformBuilder = new ValidationResult.Builder().subject(JSLT_TRANSFORM.getDisplayName());
+            results.add(transformBuilder.valid(true).build());
         } else {
-            try {
-                final String transform = readTransform(transformProperty);
-                Parser.compileString(transform);
-                transformBuilder.valid(true);
-            } catch (final RuntimeException e) {
-                final String explanation = String.format("JSLT Transform not valid: %s", e.getMessage());
-                transformBuilder.valid(false).explanation(explanation);
-            }
+            results.add(validateJSLT(JSLT_TRANSFORM, transformProperty));
         }
 
-        results.add(transformBuilder.build());
+        final PropertyValue filterProperty = validationContext.getProperty(RESULT_FILTER);
+        results.add(validateJSLT(RESULT_FILTER, filterProperty));
+
         return results;
     }
 
+    private ValidationResult validateJSLT(PropertyDescriptor property, PropertyValue value) {
+        final ValidationResult.Builder builder = new ValidationResult.Builder().subject(property.getDisplayName());
+        try {
+            final String transform = readTransform(value);
+            getJstlExpression(transform, null);
+            builder.valid(true);
+        } catch (final RuntimeException e) {
+            final String explanation = String.format("%s not valid: %s", property.getDisplayName(), e.getMessage());
+            builder.valid(false).explanation(explanation);
+        }
+        return builder.build();
+    }
+
     @OnScheduled
     public void onScheduled(final ProcessContext context) {
         int maxTransformsToCache = context.getProperty(TRANSFORM_CACHE_SIZE).asInteger();
@@ -202,10 +225,11 @@ public class JSLTTransformJSON extends AbstractProcessor {
                 .build();
         // Precompile the transform if it hasn't been done already (and if there is no Expression Language present)
         final PropertyValue transformProperty = context.getProperty(JSLT_TRANSFORM);
+        final PropertyValue filterProperty = context.getProperty(RESULT_FILTER);
         if (!transformProperty.isExpressionLanguagePresent()) {
             try {
                 final String transform = readTransform(transformProperty);
-                transformCache.put(transform, Parser.compileString(transform));
+                transformCache.put(transform, getJstlExpression(transform, filterProperty.getValue()));
             } catch (final RuntimeException e) {
                 throw new ProcessException("JSLT Transform compilation failed", e);
             }
@@ -223,12 +247,13 @@ public class JSLTTransformJSON extends AbstractProcessor {
         final StopWatch stopWatch = new StopWatch(true);
 
         final PropertyValue transformProperty = context.getProperty(JSLT_TRANSFORM);
+        final PropertyValue filterProperty = context.getProperty(RESULT_FILTER);
         FlowFile transformed;
         final JsonFactory jsonFactory = new JsonFactory();
 
         try {
             final String transform = readTransform(transformProperty, original);
-            final Expression jsltExpression = transformCache.get(transform, currString -> Parser.compileString(transform));
+            final Expression jsltExpression = transformCache.get(transform, currString -> getJstlExpression(transform, filterProperty.getValue()));
             final boolean prettyPrint = context.getProperty(PRETTY_PRINT).asBoolean();
 
             transformed = session.write(original, (inputStream, outputStream) -> {
@@ -296,8 +321,19 @@ public class JSLTTransformJSON extends AbstractProcessor {
     @OnStopped
     @OnShutdown
     public void onStopped() {
+        if (transformCache != null) {
             transformCache.cleanUp();
         }
+    }
+
+    private Expression getJstlExpression(String transform, String jsltFilter) {
+        Parser parser = new Parser(new StringReader(transform))
+                .withSource("<inline>");
+        if (jsltFilter != null && !jsltFilter.isEmpty() && !jsltFilter.equals(JSLT_FILTER_DEFAULT)) {
+            parser = parser.withObjectFilter(jsltFilter);
+        }
+        return parser.compile();
+    }
 
     private JsonNode readJson(final InputStream in) throws IOException {
         try {
@@ -321,6 +357,9 @@ public class JSLTTransformJSON extends AbstractProcessor {
 
     private String readTransform(final PropertyValue propertyValue) {
         final ResourceReference resourceReference = propertyValue.asResource();
+        if (resourceReference == null) {
+            return propertyValue.getValue();
+        }
         try (final BufferedReader reader = new BufferedReader(new InputStreamReader(resourceReference.read()))) {
             return reader.lines().collect(Collectors.joining());
         } catch (final IOException e) {

nifi-nar-bundles/nifi-jslt-bundle/nifi-jslt-processors/src/test/java/org/apache/nifi/processors/jslt/TestJSLTTransformJSON.java

@@ -151,6 +151,30 @@ public class TestJSLTTransformJSON {
         flowFile.assertContentEquals(new byte[0]);
     }
 
+    @Test
+    public void testTransformWithNullValueRemoved() {
+        runner.setProperty(JSLTTransformJSON.RESULT_FILTER, ". != null and . != {} and . != []");
+        runTransform("inputWithNull.json", "simpleTransform.json", "simpleOutputWithoutNull.json");
+    }
+
+    @Test
+    public void testTransformWithNullValueIncluded() {
+        runner.setProperty(JSLTTransformJSON.RESULT_FILTER, ". != {} and . != []");
+        runTransform("inputWithNull.json", "simpleTransform.json", "simpleOutputWithNull.json");
+    }
+
+    @Test
+    public void testTransformWithNoFilter() {
+        runner.setProperty(JSLTTransformJSON.RESULT_FILTER, "true");
+        runTransform("inputWithNull.json", "simpleTransform.json", "simpleOutputWithNull.json");
+    }
+
+    // This test verifies transformCache cleanup does not throw an exception
+    @Test
+    public void testShutdown() {
+        runner.stop();
+    }
+
     private void runTransform(final String inputFileName, final String transformFileName, final String outputFileName) {
         setTransformEnqueueJson(transformFileName, inputFileName);
 

nifi-nar-bundles/nifi-jslt-bundle/nifi-jslt-processors/src/test/resources/inputWithNull.json

@@ -0,0 +1,13 @@
+{
+  "rating": {
+    "primary": {
+      "value": 3
+    },
+    "series": {
+      "value": [5,4]
+    },
+    "quality": {
+      "value": null
+    }
+  }
+}

nifi-nar-bundles/nifi-jslt-bundle/nifi-jslt-processors/src/test/resources/simpleOutputWithNull.json

@@ -0,0 +1,8 @@
+{
+  "SecondaryRatings" : {
+    "quality" : {
+      "Value" : 3,
+      "RatingRange" : null
+    }
+  }
+}

nifi-nar-bundles/nifi-jslt-bundle/nifi-jslt-processors/src/test/resources/simpleOutputWithoutNull.json

@@ -0,0 +1,7 @@
+{
+  "SecondaryRatings" : {
+    "quality" : {
+      "Value" : 3
+    }
+  }
+}