code: /*
   * Copyright (c) 2019 the Eclipse Milo Authors
   *
   * This program and the accompanying materials are made
   * available under the terms of the Eclipse Public License 2.0
   * which is available at https://www.eclipse.org/legal/epl-2.0/
   *
   * SPDX-License-Identifier: EPL-2.0
   */
  
  package org.eclipse.milo.opcua.stack.core.util;
  
  import java.io.IOException;
  import java.io.InputStream;
  import java.net.URI;
  import java.net.URL;
  import java.util.Collections;
  import java.util.Enumeration;
  import java.util.HashSet;
  import java.util.Map;
  import java.util.Optional;
  import java.util.Set;
  import java.util.jar.Attributes;
  import java.util.jar.Manifest;
  
  import com.google.common.collect.Maps;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  public class ManifestUtil {
  
      private static final Logger logger = LoggerFactory.getLogger(ManifestUtil.class);
      private static final Map<String, String> attributes = load();
  
      public static Optional<String> read(String name) {
          return Optional.ofNullable(attributes.get(name));
      }
  
      public static boolean exists(String name) {
          return attributes.containsKey(name);
      }
  
      private static Map<String, String> load() {
          Map<String, String> attributes = Maps.newConcurrentMap();
  
          for (URI uri : uris()) {
              try {
                  attributes.putAll(load(uri.toURL()));
              } catch (Throwable t) {
                  logger.error("load(): '{}' failed", uri, t);
              }
          }
  
          return attributes;
      }
  
      private static Map<String, String> load(URL url) throws IOException {
          return load(url.openStream());
      }
  
      private static Map<String, String> load(InputStream stream) {
          Map<String, String> props = Maps.newConcurrentMap();
  
          try {
              Manifest manifest = new Manifest(stream);
              Attributes attributes = manifest.getMainAttributes();
  
              for (Object key : attributes.keySet()) {
                  String value = attributes.getValue((Attributes.Name) key);
                  props.put(key.toString(), value);
              }
          } catch (Throwable t) {
              logger.error("#load(): failed", t);
          } finally {
              try {
                  stream.close();
              } catch (IOException e) {
                  // ignored
              }
          }
  
          return props;
      }
  
      private static Set<URI> uris() {
          try {
              Enumeration<URL> resources = ManifestUtil.class
                  .getClassLoader()
                  .getResources("META-INF/MANIFEST.MF");
  
              Set<URI> uris = new HashSet<>();
              while (resources.hasMoreElements()) {
                  uris.add(resources.nextElement().toURI());
              }
  
              return uris;
          } catch (Throwable t) {
              logger.error("uris() failed", t);
              return Collections.emptySet();
          }
      }
  
  }
  