content: /*
   * 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.calcite.avatica.server;
  
  import org.apache.calcite.avatica.metrics.MetricsSystem;
  import org.apache.calcite.avatica.metrics.MetricsSystemConfiguration;
  import org.apache.calcite.avatica.metrics.MetricsSystemFactory;
  import org.apache.calcite.avatica.metrics.MetricsSystemLoader;
  import org.apache.calcite.avatica.metrics.noop.NoopMetricsSystem;
  import org.apache.calcite.avatica.metrics.noop.NoopMetricsSystemConfiguration;
  import org.apache.calcite.avatica.remote.Driver;
  import org.apache.calcite.avatica.remote.Service;
  
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import java.util.ArrayList;
  import java.util.List;
  import java.util.ServiceLoader;
  
  /**
   * Factory that instantiates the desired implementation, typically differing on the method
   * used to serialize messages, for use in the Avatica server.
   */
  public class HandlerFactory {
    private static final Logger LOG = LoggerFactory.getLogger(HandlerFactory.class);
  
    /**
     * Constructs the desired implementation for the given serialization method with metrics.
     *
     * @param service The underlying {@link Service}.
     * @param serialization The desired message serialization.
     * @return The {@link AvaticaHandler}.
     */
    public AvaticaHandler getHandler(Service service, Driver.Serialization serialization) {
      return getHandler(service, serialization, NoopMetricsSystemConfiguration.getInstance());
    }
  
    /**
     * Constructs the desired implementation for the given serialization method and server
     * configuration with metrics.
     *
     * @param service The underlying {@link Service}.
     * @param serialization The desired message serialization.
     * @param serverConfig Avatica server configuration or null.
     * @return The {@link AvaticaHandler}.
     */
    public AvaticaHandler getHandler(Service service, Driver.Serialization serialization,
        AvaticaServerConfiguration serverConfig) {
      return getHandler(service, serialization, NoopMetricsSystemConfiguration.getInstance(),
          serverConfig);
    }
  
    /**
     * Constructs the desired implementation for the given serialization method with metrics.
     *
     * @param service The underlying {@link Service}.
     * @param serialization The desired message serialization.
     * @param metricsConfig Configuration for the {@link MetricsSystem}.
     * @return The {@link AvaticaHandler}.
     */
    public AvaticaHandler getHandler(Service service, Driver.Serialization serialization,
        MetricsSystemConfiguration<?> metricsConfig) {
      return getHandler(service, serialization, metricsConfig, null);
    }
  
    /**
     * Constructs the desired implementation for the given serialization method and server
     * configuration with metrics.
     *
     * @param service The underlying {@link Service}
     * @param serialization The serializatio mechanism to use
     * @param metricsConfig Configuration for the {@link MetricsSystem}.
     * @param serverConfig Avatica server configuration or null
     * @return An {@link AvaticaHandler}
     */
    public AvaticaHandler getHandler(Service service, Driver.Serialization serialization,
        MetricsSystemConfiguration<?> metricsConfig, AvaticaServerConfiguration serverConfig) {
      if (null == metricsConfig) {
        metricsConfig = NoopMetricsSystemConfiguration.getInstance();
      }
      MetricsSystem metrics = MetricsSystemLoader.load(metricsConfig);
  
      switch (serialization) {
      case JSON:
        return new AvaticaJsonHandler(service, metrics, serverConfig);
      case PROTOBUF:
        return new AvaticaProtobufHandler(service, metrics, serverConfig);
      default:
        throw new IllegalArgumentException("Unknown Avatica handler for " + serialization.name());
      }
    }
  
    /**
     * Load a {@link MetricsSystem} using ServiceLoader to create a {@link MetricsSystemFactory}.
     *
     * @param config State to pass to the factory for initialization.
     * @return A {@link MetricsSystem} instance.
     */
    MetricsSystem loadMetricsSystem(MetricsSystemConfiguration<?> config) {
      ServiceLoader<MetricsSystemFactory> loader = ServiceLoader.load(MetricsSystemFactory.class);
      List<MetricsSystemFactory> availableFactories = new ArrayList<>();
      for (MetricsSystemFactory factory : loader) {
        availableFactories.add(factory);
      }
  
      if (1 == availableFactories.size()) {
        // One and only one instance -- what we want
        MetricsSystemFactory factory = availableFactories.get(0);
        LOG.info("Loaded MetricsSystem {}", factory.getClass());
        return factory.create(config);
      } else if (availableFactories.isEmpty()) {
        // None-provided default to no metrics
        LOG.info("No metrics implementation available on classpath. Using No-op implementation");
        return NoopMetricsSystem.getInstance();
      } else {
        // Tell the user they're doing something wrong, and choose the first impl.
        StringBuilder sb = new StringBuilder();
        for (MetricsSystemFactory factory : availableFactories) {
          if (sb.length() > 0) {
            sb.append(", ");
          }
          sb.append(factory.getClass());
        }
        LOG.warn("Found multiple MetricsSystemFactory implementations: {}."
            + " Using No-op implementation", sb);
        return NoopMetricsSystem.getInstance();
      }
    }
  }
  
  // End HandlerFactory.java
  