NIFI-9587 Add json output for Prometheus metrics

nifi-nar-bundles/nifi-framework-bundle/nifi-framework/nifi-web/nifi-web-api/src/main/java/org/apache/nifi/web/api/FlowResource.java

@@ -111,6 +111,7 @@
 import org.apache.nifi.web.api.entity.VersionedFlowSnapshotMetadataEntity;
 import org.apache.nifi.web.api.entity.VersionedFlowSnapshotMetadataSetEntity;
 import org.apache.nifi.web.api.entity.VersionedFlowsEntity;
+import org.apache.nifi.web.api.metrics.JsonFormatPrometheusMetricsWriter;
 import org.apache.nifi.web.api.metrics.TextFormatPrometheusMetricsWriter;
 import org.apache.nifi.web.api.metrics.PrometheusMetricsWriter;
 import org.apache.nifi.web.api.request.BulletinBoardPatternParameter;
@@ -428,7 +429,11 @@ public Response getFlowMetrics(
             @ApiParam(
                     value = "Regular Expression Pattern to be applied against the sample label value field"
             )
-            @QueryParam("sampleLabelValue") final String sampleLabelValue
+            @QueryParam("sampleLabelValue") final String sampleLabelValue,
+            @ApiParam(
+                    value = "Name of the first field of JSON object. Applicable for JSON producer only."
+            )
+            @QueryParam("rootFieldName") final String rootFieldName
     ) {
 
         authorizeFlow();
@@ -442,6 +447,16 @@ public Response getFlowMetrics(
                 prometheusMetricsWriter.write(registries, outputStream);
             });
             return generateOkResponse(response).type(TextFormat.CONTENT_TYPE_004).build();
+
+        } else if (FlowMetricsProducer.JSON.getProducer().equals(producer)) {
+            final StreamingOutput output = outputStream -> {
+                final JsonFormatPrometheusMetricsWriter jsonPrometheusMetricsWriter = new JsonFormatPrometheusMetricsWriter(sampleName, sampleLabelValue, rootFieldName);
+                jsonPrometheusMetricsWriter.write(registries, outputStream);
+            };
+            return generateOkResponse(output)
+                    .type(MediaType.APPLICATION_JSON_TYPE)
+                    .build();
+
         } else {
             throw new ResourceNotFoundException("The specified producer is missing or invalid.");
         }

nifi-nar-bundles/nifi-framework-bundle/nifi-framework/nifi-web/nifi-web-api/src/main/java/org/apache/nifi/web/api/metrics/AbstractPrometheusMetricsWriter.java

@@ -0,0 +1,49 @@
+/*
+ * 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.web.api.metrics;
+
+import io.prometheus.client.Collector;
+import io.prometheus.client.CollectorRegistry;
+import org.apache.commons.lang3.StringUtils;
+import java.util.Enumeration;
+import java.util.regex.Pattern;
+
+public abstract class AbstractPrometheusMetricsWriter implements PrometheusMetricsWriter {
+    private final Pattern sampleNamePattern;
+
+    private final Pattern sampleLabelValuePattern;
+
+    private final boolean filteringDisabled;
+
+    public AbstractPrometheusMetricsWriter(
+            final String sampleName,
+            final String sampleLabelValue
+    ) {
+        this.sampleNamePattern = StringUtils.isBlank(sampleName) ? null : Pattern.compile(sampleName);
+        this.sampleLabelValuePattern = StringUtils.isBlank(sampleLabelValue) ? null : Pattern.compile(sampleLabelValue);
+        this.filteringDisabled = StringUtils.isAllBlank(sampleName, sampleLabelValue);
+    }
+
+    Enumeration<Collector.MetricFamilySamples> getSamples(final CollectorRegistry registry) {
+        final Enumeration<Collector.MetricFamilySamples> samples = registry.metricFamilySamples();
+        return filteringDisabled ? samples : new FilteringMetricFamilySamplesEnumeration(
+                samples,
+                sampleNamePattern,
+                sampleLabelValuePattern
+        );
+    }
+}

nifi-nar-bundles/nifi-framework-bundle/nifi-framework/nifi-web/nifi-web-api/src/main/java/org/apache/nifi/web/api/metrics/JsonFormatPrometheusMetricsWriter.java

@@ -0,0 +1,69 @@
+/*
+ * 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.web.api.metrics;
+
+import com.fasterxml.jackson.core.JsonFactory;
+import com.fasterxml.jackson.core.JsonGenerator;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import io.prometheus.client.Collector;
+import io.prometheus.client.CollectorRegistry;
+
+import java.io.BufferedWriter;
+import java.io.IOException;
+import java.io.OutputStream;
+import java.io.OutputStreamWriter;
+import java.io.Writer;
+import java.util.Collection;
+import java.util.Enumeration;
+
+/**
+ * Prometheus Metrics Writer with Json output format and optional filtering
+ */
+public class JsonFormatPrometheusMetricsWriter extends AbstractPrometheusMetricsWriter {
+    private final String firstFieldName;
+
+    public JsonFormatPrometheusMetricsWriter(final String sampleName, final String sampleLabelValue, final String firstFieldName) {
+        super(sampleName, sampleLabelValue);
+        this.firstFieldName = firstFieldName == null ? "samples" : firstFieldName;
+    }
+
+    @Override
+    public void write(final Collection<CollectorRegistry> registries, final OutputStream outputStream) throws IOException {
+        JsonFactory factory = new JsonFactory();
+        try (final Writer writer = new BufferedWriter(new OutputStreamWriter(outputStream));
+        final JsonGenerator generator = factory.createGenerator(writer)) {
+            generator.setCodec(new ObjectMapper());
+            generator.writeStartObject();
+            generator.writeFieldName(firstFieldName);
+            generator.writeStartArray();
+            for (final CollectorRegistry collectorRegistry : registries) {
+                final Enumeration<Collector.MetricFamilySamples> samples = getSamples(collectorRegistry);
+                while (samples.hasMoreElements()) {
+                    final Collector.MetricFamilySamples samples2 = samples.nextElement();
+                    for (Collector.MetricFamilySamples.Sample sample : samples2.samples) {
+                        generator.writeObject(sample);
+                        generator.flush();
+                    }
+                    generator.flush();
+                }
+            }
+            generator.writeEndArray();
+            generator.writeEndObject();
+            generator.flush();
+        }
+    }
+}

nifi-nar-bundles/nifi-framework-bundle/nifi-framework/nifi-web/nifi-web-api/src/main/java/org/apache/nifi/web/api/metrics/TextFormatPrometheusMetricsWriter.java

@@ -19,7 +19,6 @@
 import io.prometheus.client.Collector;
 import io.prometheus.client.CollectorRegistry;
 import io.prometheus.client.exporter.common.TextFormat;
-import org.apache.commons.lang3.StringUtils;
 
 import java.io.BufferedWriter;
 import java.io.IOException;
@@ -28,25 +27,14 @@
 import java.io.Writer;
 import java.util.Collection;
 import java.util.Enumeration;
-import java.util.regex.Pattern;
 
 /**
  * Prometheus Metrics Writer supporting Prometheus Text Version 0.0.4 with optional filtering
  */
-public class TextFormatPrometheusMetricsWriter implements PrometheusMetricsWriter {
-    private final Pattern sampleNamePattern;
+public class TextFormatPrometheusMetricsWriter extends AbstractPrometheusMetricsWriter {
 
-    private final Pattern sampleLabelValuePattern;
-
-    private final boolean filteringDisabled;
-
-    public TextFormatPrometheusMetricsWriter(
-            final String sampleName,
-            final String sampleLabelValue
-    ) {
-        this.sampleNamePattern = StringUtils.isBlank(sampleName) ? null : Pattern.compile(sampleName);
-        this.sampleLabelValuePattern = StringUtils.isBlank(sampleLabelValue) ? null : Pattern.compile(sampleLabelValue);
-        this.filteringDisabled = StringUtils.isAllBlank(sampleName, sampleLabelValue);
+    public TextFormatPrometheusMetricsWriter(final String sampleName, final String sampleLabelValue) {
+        super(sampleName, sampleLabelValue);
     }
 
     @Override
@@ -59,13 +47,4 @@ public void write(final Collection<CollectorRegistry> registries, final OutputSt
             }
         }
     }
-
-    private Enumeration<Collector.MetricFamilySamples> getSamples(final CollectorRegistry registry) {
-        final Enumeration<Collector.MetricFamilySamples> samples = registry.metricFamilySamples();
-        return filteringDisabled ? samples : new FilteringMetricFamilySamplesEnumeration(
-                samples,
-                sampleNamePattern,
-                sampleLabelValuePattern
-        );
-    }
 }

nifi-nar-bundles/nifi-framework-bundle/nifi-framework/nifi-web/nifi-web-api/src/main/java/org/apache/nifi/web/api/request/FlowMetricsProducer.java

@@ -20,7 +20,8 @@
  * Flow Metrics Producers supported
  */
 public enum FlowMetricsProducer {
-    PROMETHEUS("prometheus");
+    PROMETHEUS("prometheus"),
+    JSON("json");
 
     private final String producer;