content: /*
   * The Alluxio Open Foundation licenses this work under the Apache License, version 2.0
   * (the "License"). You may not use this work except in compliance with the License, which is
   * available at www.apache.org/licenses/LICENSE-2.0
   *
   * This software is distributed on an "AS IS" basis, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
   * either express or implied, as more fully set forth in the License.
   *
   * See the NOTICE file distributed with this work for information regarding copyright ownership.
   */
  
  package alluxio.metrics.sink;
  
  import com.codahale.metrics.MetricRegistry;
  import com.codahale.metrics.json.MetricsModule;
  import com.fasterxml.jackson.databind.ObjectMapper;
  import org.eclipse.jetty.servlet.ServletContextHandler;
  import org.eclipse.jetty.servlet.ServletHolder;
  
  import java.io.IOException;
  import java.util.Properties;
  import java.util.concurrent.TimeUnit;
  import javax.annotation.concurrent.NotThreadSafe;
  import javax.servlet.ServletException;
  import javax.servlet.http.HttpServlet;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  
  /**
   * A sink that exposes metrics data in JSON format by HTTP.
   */
  @NotThreadSafe
  public class MetricsServlet implements Sink {
    public static final String SERVLET_PATH = "/metrics/json";
    public static final ObjectMapper OBJECT_MAPPER = new ObjectMapper()
        .registerModule(new MetricsModule(TimeUnit.SECONDS, TimeUnit.MILLISECONDS, false));
  
    private MetricRegistry mMetricsRegistry;
  
    /**
     * Creates a new {@link MetricsServlet} with a {@link Properties} and {@link MetricRegistry}.
     *
     * @param registry the metric registry to register
     */
    public MetricsServlet(MetricRegistry registry) {
      mMetricsRegistry = registry;
    }
  
    private HttpServlet createServlet() {
      return new HttpServlet() {
        private static final long serialVersionUID = -2761243531478788172L;
  
        @Override
        protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
          response.setContentType("application/json");
          response.setStatus(HttpServletResponse.SC_OK);
          response.setHeader("Cache-Control", "no-cache, no-store, must-revalidate");
          String result = OBJECT_MAPPER.writerWithDefaultPrettyPrinter()
              .writeValueAsString(mMetricsRegistry);
          response.getWriter().println(result);
        }
      };
    }
  
    /**
     * Gets the {@link ServletContextHandler} of the metrics servlet.
     *
     * @return the {@link ServletContextHandler} object
     */
    public ServletContextHandler getHandler() {
      ServletContextHandler contextHandler = new ServletContextHandler();
      contextHandler.setContextPath(SERVLET_PATH);
      contextHandler.addServlet(new ServletHolder(createServlet()), "/");
      return contextHandler;
    }
  
    @Override
    public void start() {}
  
    @Override
    public void stop() {}
  
    @Override
    public void report() {}
  }
  