bookkeeper-stats-providers/prometheus-metrics-provider/src/main/java/org/apache/bookkeeper/stats/prometheus/PrometheusServlet.java

/**
 * 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.bookkeeper.stats.prometheus;

import io.prometheus.client.exporter.common.TextFormat;

import java.io.IOException;
import java.io.Writer;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet used to export metrics in prometheus text format.
 */
public class PrometheusServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    private final transient PrometheusMetricsProvider provider;

    public PrometheusServlet(PrometheusMetricsProvider provider) {
        this.provider = provider;
    }

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setStatus(HttpServletResponse.SC_OK);
        resp.setContentType(TextFormat.CONTENT_TYPE_004);

        Writer writer = resp.getWriter();
        try {
            provider.writeAllMetrics(writer);
            writer.flush();
        } finally {
            writer.close();
        }
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }

}