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.ambari.server.checks;
  
  import java.util.Set;
  
  import org.apache.ambari.spi.upgrade.UpgradeCheck;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  import org.springframework.beans.factory.config.BeanDefinition;
  import org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider;
  import org.springframework.core.type.filter.AssignableTypeFilter;
  import org.springframework.util.ClassUtils;
  
  import com.google.inject.Inject;
  import com.google.inject.Injector;
  import com.google.inject.Provider;
  
  /**
   * The {@link UpgradeCheckRegistryProvider} is a provider which binds any
   * requests for the {@link UpgradeCheckRegistry}. When first requested, it will
   * perform a classpath scan looking for instances of {@link UpgradeCheck} and
   * then return an initialized {@link UpgradeCheckRegistry}.
   */
  public class UpgradeCheckRegistryProvider implements Provider<UpgradeCheckRegistry> {
  
    /**
     * Logger.
     */
    private static final Logger LOG = LoggerFactory.getLogger(UpgradeCheckRegistryProvider.class);
  
    /**
     * Used to injecting members into the {@link UpgradeCheck} instances which are
     * discovered.
     */
    @Inject
    private Injector m_injector;
  
    /**
     * The singleton registry to inject with found checks.
     */
    private UpgradeCheckRegistry m_checkRegistry;
  
    /**
     * The scanned instances of {@link UpgradeCheck} from the classpath.
     */
    private Set<BeanDefinition> m_beanDefinitions = null;
  
    /**
     * {@inheritDoc}
     */
    @Override
    public UpgradeCheckRegistry get() {
      if (null == m_beanDefinitions || m_beanDefinitions.isEmpty()) {
        String packageName = ClusterCheck.class.getPackage().getName();
        LOG.info("Searching package {} for classes matching {}", packageName, UpgradeCheck.class);
  
        ClassPathScanningCandidateComponentProvider scanner = new ClassPathScanningCandidateComponentProvider(false);
  
        // match all implementations of the base check class
        AssignableTypeFilter filter = new AssignableTypeFilter(UpgradeCheck.class);
        scanner.addIncludeFilter(filter);
  
        m_beanDefinitions = scanner.findCandidateComponents(packageName);
      }
  
      // no checks is a problem
      if (null == m_beanDefinitions || m_beanDefinitions.size() == 0) {
        LOG.error("No instances of {} found to register", UpgradeCheck.class);
        return null;
      }
  
      m_checkRegistry = new UpgradeCheckRegistry();
      m_injector.injectMembers(m_checkRegistry);
  
      // for every discovered check, singleton-ize them and register with the
      // registry
      for (BeanDefinition beanDefinition : m_beanDefinitions) {
        String className = beanDefinition.getBeanClassName();
        Class<?> clazz = ClassUtils.resolveClassName(className, ClassUtils.getDefaultClassLoader());
  
        try {
          UpgradeCheck upgradeCheck = (UpgradeCheck) m_injector.getInstance(clazz);
          m_checkRegistry.register(upgradeCheck);
  
          LOG.info("Registered pre-upgrade check {}", upgradeCheck.getClass());
        } catch (Exception exception) {
          LOG.error("Unable to bind and register upgrade check {}", clazz, exception);
        }
      }
  
      return m_checkRegistry;
    }
  }
  