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Apache Hadoop Common

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/**
 * 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.hadoop.http;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

import org.apache.hadoop.metrics2.lib.DefaultMetricsSystem;
import org.apache.hadoop.metrics2.sink.PrometheusMetricsSink;

/**
 * Servlet to publish hadoop metrics in prometheus format.
 */
public class PrometheusServlet extends HttpServlet {

  public PrometheusMetricsSink getPrometheusSink() {
    return
        (PrometheusMetricsSink) getServletContext().getAttribute(
            HttpServer2.PROMETHEUS_SINK);
  }

  @Override
  protected void doGet(HttpServletRequest req, HttpServletResponse resp)
      throws ServletException, IOException {
    DefaultMetricsSystem.instance().publishMetricsNow();
    getPrometheusSink().writeMetrics(resp.getWriter());
    resp.getWriter().flush();
  }
}