本文整理了Java中java.util.stream.Collectors.groupingBy()方法的一些代码示例，展示了Collectors.groupingBy()的具体用法。这些代码示例主要来源于Github/Stackoverflow/Maven等平台，是从一些精选项目中提取出来的代码，具有较强的参考意义，能在一定程度帮忙到你。Collectors.groupingBy()方法的具体详情如下：
包路径：java.util.stream.Collectors
类名称：Collectors
方法名：groupingBy

Collectors.groupingBy介绍

暂无

代码示例

代码示例来源：origin: neo4j/neo4j

private Stream<Map.Entry<String,List<Element>>> indexByName( Collection<Element> visitedProcedures )
{
  return visitedProcedures.stream().collect( groupingBy( this::getName ) ).entrySet().stream();
}

代码示例来源：origin: google/error-prone

/**
 * Returns a collection of method groups for given list of {@code classMethods}.
 *
 * <p>A <i>method group</i> is a list of methods with the same name.
 *
 * <p>It is assumed that given {@code classMethods} really do belong to the same class. The
 * returned collection does not guarantee any particular group ordering.
 */
private static Collection<List<MethodTree>> getMethodGroups(List<MethodTree> classMethods) {
 return classMethods.stream().collect(groupingBy(MethodTree::getName)).values();
}

代码示例来源：origin: SonarSource/sonarqube

public Helper() {
 InputStream inputStream = Helper.class.getResourceAsStream("/responseClasses.config");
 responseTypes = new BufferedReader(new InputStreamReader(inputStream))
  .lines()
  .map(line -> line.split("\\s+"))
  .collect(Collectors.groupingBy(arr -> arr[0]));
}

代码示例来源：origin: RichardWarburton/java-8-lambdas-exercises

public Map<Artist, Integer> numberOfAlbumsDumb(Stream<Album> albums) {
    // BEGIN NUMBER_OF_ALBUMS_DUMB
Map<Artist, List<Album>> albumsByArtist
  = albums.collect(groupingBy(album -> album.getMainMusician()));

Map<Artist, Integer>  numberOfAlbums = new HashMap<>();
for(Entry<Artist, List<Album>> entry : albumsByArtist.entrySet()) {
  numberOfAlbums.put(entry.getKey(), entry.getValue().size());
}
    // END NUMBER_OF_ALBUMS_DUMB
    return numberOfAlbums;
  }

代码示例来源：origin: goldmansachs/gs-collections

@Benchmark
public Map<Boolean, Set<Integer>> groupBy_2_keys_serial_lazy_jdk()
{
  Map<Boolean, Set<Integer>> multimap = this.integersJDK.stream()
      .collect(Collectors.groupingBy(each -> each % 2 == 0, Collectors.toSet()));
  Verify.assertSize(2, multimap);
  return multimap;
}

代码示例来源：origin: confluentinc/ksql

public static Collection<Double> currentConsumptionRateByQuery() {
 return collectorMap.values()
   .stream()
   .filter(collector -> collector.getGroupId() != null)
   .collect(
     Collectors.groupingBy(
      MetricCollector::getGroupId,
      Collectors.summingDouble(
        m -> m.aggregateStat(ConsumerCollector.CONSUMER_MESSAGES_PER_SEC, false)
      )
    )
   )
   .values();
}

代码示例来源：origin: stackoverflow.com

import java.util.*;
import java.util.stream.*;

class Test {
  public static void main(String[] args) {
    List<String> list = new ArrayList<>();

    list.add("Hello");
    list.add("Hello");
    list.add("World");

    Map<String, Long> counted = list.stream()
      .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));

    System.out.println(counted);
  }
}

代码示例来源：origin: apache/flink

@Override
  @Nonnull
  Map<String, String> expected(@Nonnull List<ValueWithTs<Tuple2<String, String>>> updates, long currentTimestamp) {
    return updates.stream()
      .collect(Collectors.groupingBy(u -> u.getValue().f0))
      .entrySet().stream()
      .map(e -> e.getValue().get(e.getValue().size() - 1))
      .filter(u -> !expired(u.getTimestamp(), currentTimestamp))
      .map(ValueWithTs::getValue)
      .collect(Collectors.toMap(u -> u.f0, u -> u.f1));
  }
}

代码示例来源：origin: apache/storm

private Collection<List<ProcessorNode>> parallelismGroups(List<ProcessorNode> processorNodes) {
  return processorNodes.stream().collect(Collectors.groupingBy(Node::getParallelism)).values();
}

代码示例来源：origin: apache/nifi

public Map<QueuePartition, List<FlowFileRecord>> distributeToPartitionsAndGet(final Collection<FlowFileRecord> flowFiles) {
  if (flowFiles == null || flowFiles.isEmpty()) {
    return Collections.emptyMap();
  }
  final Map<QueuePartition, List<FlowFileRecord>> partitionMap;
  partitionReadLock.lock();
  try {
    // Optimize for the most common case (no load balancing) so that we will just call getPartition() for the first FlowFile
    // in the Collection and then put all FlowFiles into that QueuePartition. Is fairly expensive to call stream().collect(#groupingBy).
    if (partitioner.isPartitionStatic()) {
      final QueuePartition partition = getPartition(flowFiles.iterator().next());
      partition.putAll(flowFiles);
      final List<FlowFileRecord> flowFileList = (flowFiles instanceof List) ? (List<FlowFileRecord>) flowFiles : new ArrayList<>(flowFiles);
      partitionMap = Collections.singletonMap(partition, flowFileList);
      logger.debug("Partitioner is static so Partitioned FlowFiles as: {}", partitionMap);
      return partitionMap;
    }
    partitionMap = flowFiles.stream().collect(Collectors.groupingBy(this::getPartition));
    logger.debug("Partitioned FlowFiles as: {}", partitionMap);
    for (final Map.Entry<QueuePartition, List<FlowFileRecord>> entry : partitionMap.entrySet()) {
      final QueuePartition partition = entry.getKey();
      final List<FlowFileRecord> flowFilesForPartition = entry.getValue();
      partition.putAll(flowFilesForPartition);
    }
  } finally {
    partitionReadLock.unlock();
  }
  return partitionMap;
}

代码示例来源：origin: goldmansachs/gs-collections

@Benchmark
public Map<Integer, Set<Integer>> groupBy_100_keys_serial_lazy_jdk()
{
  Map<Integer, Set<Integer>> multimap = this.integersJDK.stream().collect(Collectors.groupingBy(each -> each % 100, Collectors.toSet()));
  Verify.assertSize(100, multimap);
  return multimap;
}

代码示例来源：origin: gocd/gocd

public Collection<CombinedPluginInfo> allPluginInfos(String type) {
  if (isBlank(type)) {
    return builders.values().stream()
        .map((Function<MetadataStore, Collection<? extends PluginInfo>>) MetadataStore::allPluginInfos)
        .flatMap((Function<Collection<? extends PluginInfo>, Stream<? extends PluginInfo>>) Collection::stream)
        .collect(Collectors.groupingBy(pluginID(), toCollection(CombinedPluginInfo::new)))
        .values();
  } else if (builders.containsKey(type)) {
    Collection<PluginInfo> pluginInfosForType = builders.get(type).allPluginInfos();
    return pluginInfosForType.stream()
        .map(CombinedPluginInfo::new).collect(toList());
  } else {
    throw new InvalidPluginTypeException();
  }
}

代码示例来源：origin: Graylog2/graylog2-server

@GET
@RequiresPermissions(RestPermissions.USERS_LIST)
@ApiOperation(value = "List all users", notes = "The permissions assigned to the users are always included.")
public UserList listUsers() {
  final List<User> users = userService.loadAll();
  final Collection<MongoDbSession> sessions = sessionService.loadAll();
  // among all active sessions, find the last recently used for each user
  //noinspection OptionalGetWithoutIsPresent
  final Map<String, Optional<MongoDbSession>> lastSessionForUser = sessions.stream()
      .filter(s -> s.getUsernameAttribute().isPresent())
      .collect(groupingBy(s -> s.getUsernameAttribute().get(),
                maxBy(Comparator.comparing(MongoDbSession::getLastAccessTime))));
  final List<UserSummary> resultUsers = Lists.newArrayListWithCapacity(users.size() + 1);
  final User adminUser = userService.getAdminUser();
  resultUsers.add(toUserResponse(adminUser, lastSessionForUser.getOrDefault(adminUser.getName(), Optional.empty())));
  for (User user : users) {
    resultUsers.add(toUserResponse(user, lastSessionForUser.getOrDefault(user.getName(), Optional.empty())));
  }
  return UserList.create(resultUsers);
}

代码示例来源：origin: languagetool-org/languagetool

private void updateIgnoredWordDictionary() {
 wordsToBeIgnoredDictionary = wordsToBeIgnored
                 .stream()
                 .collect(Collectors.groupingBy(s -> s.substring(0,1), Collectors.toSet()));
 wordsToBeIgnoredDictionaryIgnoreCase = wordsToBeIgnored
                      .stream()
                      .map(s -> s.toLowerCase())
                      .collect(Collectors.groupingBy(s -> s.substring(0,1), Collectors.toSet()));
}

代码示例来源：origin: neo4j/neo4j

public void forEach( BiConsumer<String,URI> consumer )
{
  entries.stream().collect( Collectors.groupingBy( e -> e.key ) )
      .forEach( ( key, list ) -> list.stream()
          .max( Comparator.comparing( e -> e.precedence ) )
          .ifPresent( e -> consumer.accept( key, e.uri ) ) );
}

代码示例来源：origin: checkstyle/checkstyle

/**
 * Generate the map of third party Checkstyle module names to the set of their fully qualified
 * names.
 * @param loader the class loader used to load Checkstyle package names
 * @return the map of third party Checkstyle module names to the set of their fully qualified
 *      names
 */
private Map<String, Set<String>> generateThirdPartyNameToFullModuleName(ClassLoader loader) {
  Map<String, Set<String>> returnValue;
  try {
    returnValue = ModuleReflectionUtil.getCheckstyleModules(packages, loader).stream()
      .collect(Collectors.groupingBy(Class::getSimpleName,
        Collectors.mapping(Class::getCanonicalName, Collectors.toSet())));
  }
  catch (IOException ignore) {
    returnValue = Collections.emptyMap();
  }
  return returnValue;
}

代码示例来源：origin: SonarSource/sonarqube

private static void ensureNoDuplicateName(Set<CoreExtension> coreExtensions) {
 Map<String, Long> nameCounts = coreExtensions.stream()
  .map(CoreExtension::getName)
  .collect(Collectors.groupingBy(t -> t, Collectors.counting()));
 Set<String> duplicatedNames = nameCounts.entrySet().stream()
  .filter(t -> t.getValue() > 1)
  .map(Map.Entry::getKey)
  .collect(MoreCollectors.toSet());
 checkState(duplicatedNames.isEmpty(),
  "Multiple core extensions declare the following names: %s",
  duplicatedNames.stream().sorted().collect(Collectors.joining(", ")));
}

代码示例来源：origin: neo4j/neo4j

private Map<AdminCommandSection,List<AdminCommand.Provider>> groupProvidersBySection()
  {
    List<AdminCommand.Provider> providers = new ArrayList<>();
    commands.getAllProviders().forEach( providers::add );
    return providers.stream().collect( Collectors.groupingBy( AdminCommand.Provider::commandSection ) );
  }
}

代码示例来源：origin: apache/nifi

/**
 * Set input or output DataSet ids for a NiFiFlowPath.
 * The updated ids only containing active ids.
 * @return True if there is any changed IO reference (create, update, delete).
 */
private boolean setChangedIOIds(NiFiFlowPath path, AtlasEntity pathEntity, boolean isInput) {
  Set<AtlasObjectId> ids = isInput ? path.getInputs() : path.getOutputs();
  String targetAttribute = isInput ? ATTR_INPUTS : ATTR_OUTPUTS;
  final Map<EntityChangeType, List<AtlasObjectId>> changedIOIds
      = ids.stream().collect(Collectors.groupingBy(this::getFlowPathIOChangeType));
  // Remove DELETED references.
  final Set<AtlasObjectId> remainingFlowPathIOIds = toRemainingFlowPathIOIds(changedIOIds);
  // If references are changed, update it.
  if (path.isDataSetReferenceChanged(remainingFlowPathIOIds, isInput)) {
    pathEntity.setAttribute(targetAttribute, remainingFlowPathIOIds);
    return true;
  }
  return false;
}

代码示例来源：origin: Graylog2/graylog2-server

@Override
public Map<String, List<StreamRule>> loadForStreamIds(Collection<String> streamIds) {
  final List<ObjectId> objectIds = streamIds.stream()
    .map(ObjectId::new)
    .collect(Collectors.toList());
  final List<DBObject> respStreamRules = query(StreamRuleImpl.class,
    new BasicDBObject(StreamRuleImpl.FIELD_STREAM_ID, new BasicDBObject("$in", objectIds))
  );
  return respStreamRules.stream()
    .map(this::toStreamRule)
    .collect(Collectors.groupingBy(StreamRule::getStreamId));
}