/
MetricsServlet.java
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/
MetricsServlet.java
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/*
* Licensed to The OpenNMS Group, Inc (TOG) under one or more
* contributor license agreements. See the LICENSE.md file
* distributed with this work for additional information
* regarding copyright ownership.
*
* TOG licenses this file to You under the GNU Affero General
* Public License Version 3 (the "License") or (at your option)
* any later version. You may not use this file except in
* compliance with the License. You may obtain a copy of the
* License at:
*
* https://www.gnu.org/licenses/agpl-3.0.txt
*
* 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.opennms.horizon.minion.observability.metrics.internal;
import com.codahale.metrics.MetricRegistry;
import io.prometheus.client.Collector.MetricFamilySamples;
import io.prometheus.client.CollectorRegistry;
import io.prometheus.client.dropwizard.DropwizardExports;
import io.prometheus.client.exporter.common.TextFormat;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.Writer;
import java.util.Enumeration;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class MetricsServlet extends HttpServlet {
private static final Logger log = LoggerFactory.getLogger(MetricsServlet.class);
private final CollectorRegistry collectorRegistry;
public MetricsServlet(MetricRegistry metricRegistry) {
collectorRegistry = new CollectorRegistry();
collectorRegistry.register(new DropwizardExports(metricRegistry));
}
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) {
Enumeration<MetricFamilySamples> samples = collectorRegistry.metricFamilySamples();
try (ServletOutputStream outputStream = resp.getOutputStream()) {
try (Writer writer = new OutputStreamWriter(outputStream)) {
TextFormat.write004(writer, samples);
}
flush(outputStream, resp);
} catch (IOException e) {
log.error("Failed to write samples to output stream", e);
resp.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
}
}
private void flush(ServletOutputStream outputStream, HttpServletResponse resp) {
try {
outputStream.flush();
} catch (IOException e) {
log.error("Failed to flush samples to output stream", e);
resp.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
}
}
}