本文整理了Java中java.util.Optional.ofNullable()方法的一些代码示例，展示了Optional.ofNullable()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。Optional.ofNullable()方法的具体详情如下：
包路径：java.util.Optional
类名称：Optional
方法名：ofNullable

Optional.ofNullable介绍

[英]Returns an Optional describing the specified value, if non-null, otherwise returns an empty Optional.
[中]返回描述指定值的可选值，如果为非null，则返回空可选值。

代码示例

canonical example by Tabnine

private Double calculateAverageGrade(Map<String, List<Integer>> gradesList, String studentName)
  throws Exception {
 return Optional.ofNullable(gradesList.get(studentName))
   .map(list -> list.stream().collect(Collectors.averagingDouble(x -> x)))
   .orElseThrow(() -> new Exception("Student not found - " + studentName));
}

代码示例来源：origin: iluwatar/java-design-patterns

@Override
public Optional<Customer> getById(final int id) {
 return Optional.ofNullable(idToCustomer.get(id));
}

代码示例来源：origin: spring-projects/spring-framework

/**
 * Determine a media type for the given resource, if possible.
 * @param resource the resource to introspect
 * @return the corresponding media type, or {@code null} if none found
 */
public static Optional<MediaType> getMediaType(@Nullable Resource resource) {
  return Optional.ofNullable(resource)
      .map(Resource::getFilename)
      .flatMap(MediaTypeFactory::getMediaType);
}

代码示例来源：origin: dropwizard/dropwizard

@Override
@JsonProperty
public Optional<Duration> getValidationQueryTimeout() {
  return Optional.ofNullable(validationQueryTimeout);
}

代码示例来源：origin: dropwizard/dropwizard

@Override
public void configure(Map<String, String> options) {
  useCache = Optional.ofNullable(options.get("cache")).map(Boolean::parseBoolean).orElse(true);
  fileRoot = Optional.ofNullable(options.get("fileRoot")).map(File::new);
}

代码示例来源：origin: Netflix/eureka

/**
 * Gets the list of <em>instances</em> associated to a virtual host name.
 *
 * @param virtualHostName
 *            the virtual hostname for which the instances need to be
 *            returned.
 * @return list of <em>instances</em>.
 */
public List<InstanceInfo> getInstancesByVirtualHostName(String virtualHostName) {
  return Optional.ofNullable(this.virtualHostNameAppMap.get(virtualHostName.toUpperCase(Locale.ROOT)))
    .map(VipIndexSupport::getVipList)
    .map(AtomicReference::get)
    .orElseGet(Collections::emptyList); 
}

代码示例来源：origin: gocd/gocd

private Optional<String> parseTag(ProcessType requestType, LogLevel logLevel) {
  switch (requestType) {
    case FETCH:
      return Optional.ofNullable(FETCH_ARTIFACT_LOG_LEVEL_TAG.get(logLevel));
    case PUBLISH:
      return Optional.ofNullable(PUBLISH_ARTIFACT_LOG_LEVEL_TAG.get(logLevel));
  }
  return Optional.empty();
}

代码示例来源：origin: hs-web/hsweb-framework

public Optional<String> getStringConfig(String name) {
    return config == null ?
        Optional.empty() :
        Optional.ofNullable(config.get(name))
            .map(String::valueOf);
  }
}

代码示例来源：origin: apache/kafka

Optional<PartitionInfo> getPartitionInfo(TopicPartition topicPartition) {
  return Optional.ofNullable(metadataByPartition.get(topicPartition))
      .map(PartitionInfoAndEpoch::partitionInfo);
}

代码示例来源：origin: prestodb/presto

public List<GroupingOperation> getGroupingOperations(QuerySpecification querySpecification)
{
  return Optional.ofNullable(groupingOperations.get(NodeRef.of(querySpecification)))
      .orElse(emptyList());
}

代码示例来源：origin: spring-projects/spring-framework

/**
 * Determine the media types for the given file name, if possible.
 * @param filename the file name plus extension
 * @return the corresponding media types, or an empty list if none found
 */
public static List<MediaType> getMediaTypes(@Nullable String filename) {
  return Optional.ofNullable(StringUtils.getFilenameExtension(filename))
      .map(s -> s.toLowerCase(Locale.ENGLISH))
      .map(fileExtensionToMediaTypes::get)
      .orElse(Collections.emptyList());
}

代码示例来源：origin: apache/flink

public <R> Optional<R> map(Function<? super T, ? extends R> mapper) {
  if (value == null) {
    return Optional.empty();
  } else {
    return Optional.ofNullable(mapper.apply(value));
  }
}

代码示例来源：origin: prestodb/presto

@Override
public OptionalDouble getValueFromAggregationQueryResult(Object value)
{
  return Optional.ofNullable(value)
      .map(Number.class::cast)
      .map(Number::doubleValue)
      .map(OptionalDouble::of)
      .orElseGet(OptionalDouble::empty);
}

代码示例来源：origin: spring-projects/spring-framework

private static <T, S extends Publisher<T>> S readWithMessageReaders(
    ReactiveHttpInputMessage message, BodyExtractor.Context context, ResolvableType elementType,
    Function<HttpMessageReader<T>, S> readerFunction,
    Function<UnsupportedMediaTypeException, S> errorFunction,
    Supplier<S> emptySupplier) {
  if (VOID_TYPE.equals(elementType)) {
    return emptySupplier.get();
  }
  MediaType contentType = Optional.ofNullable(message.getHeaders().getContentType())
      .orElse(MediaType.APPLICATION_OCTET_STREAM);
  return context.messageReaders().stream()
      .filter(reader -> reader.canRead(elementType, contentType))
      .findFirst()
      .map(BodyExtractors::<T>cast)
      .map(readerFunction)
      .orElseGet(() -> {
        List<MediaType> mediaTypes = context.messageReaders().stream()
            .flatMap(reader -> reader.getReadableMediaTypes().stream())
            .collect(Collectors.toList());
        return errorFunction.apply(
            new UnsupportedMediaTypeException(contentType, mediaTypes, elementType));
      });
}

代码示例来源：origin: prestodb/presto

private Optional<QueryFailureInfo> createQueryFailureInfo(ExecutionFailureInfo failureInfo, Optional<StageInfo> outputStage)
{
  if (failureInfo == null) {
    return Optional.empty();
  }
  Optional<TaskInfo> failedTask = outputStage.flatMap(QueryMonitor::findFailedTask);
  return Optional.of(new QueryFailureInfo(
      failureInfo.getErrorCode(),
      Optional.ofNullable(failureInfo.getType()),
      Optional.ofNullable(failureInfo.getMessage()),
      failedTask.map(task -> task.getTaskStatus().getTaskId().toString()),
      failedTask.map(task -> task.getTaskStatus().getSelf().getHost()),
      executionFailureInfoCodec.toJson(failureInfo)));
}

代码示例来源：origin: spring-projects/spring-framework

private String getNameForReturnValue(MethodParameter returnType) {
  return Optional.ofNullable(returnType.getMethodAnnotation(ModelAttribute.class))
      .filter(ann -> StringUtils.hasText(ann.value()))
      .map(ModelAttribute::value)
      .orElseGet(() -> Conventions.getVariableNameForParameter(returnType));
}

代码示例来源：origin: perwendel/spark

public static String fromResource(AbstractFileResolvingResource resource) {
  String filename = Optional.ofNullable(resource.getFilename()).orElse("");
  return getMimeType(filename);
}

代码示例来源：origin: SonarSource/sonarqube

private RuleUpdate createRuleUpdate(DbSession dbSession, RuleKey key, OrganizationDto organization) {
 RuleDto rule = dbClient.ruleDao().selectByKey(dbSession, organization, key)
  .orElseThrow(() -> new NotFoundException(format("This rule does not exist: %s", key)));
 RuleUpdate ruleUpdate = ofNullable(rule.getTemplateId())
  .map(x -> RuleUpdate.createForCustomRule(key))
  .orElseGet(() -> RuleUpdate.createForPluginRule(key));
 ruleUpdate.setOrganization(organization);
 return ruleUpdate;
}

代码示例来源：origin: Netflix/eureka

/**
 * Gets the list of instances associated with this particular application.
 * <p>
 * Note that the instances are always returned with random order after
 * shuffling to avoid traffic to the same instances during startup. The
 * shuffling always happens once after every fetch cycle as specified in
 * {@link EurekaClientConfig#getRegistryFetchIntervalSeconds}.
 * </p>
 *
 * @return the list of shuffled instances associated with this application.
 */
@JsonProperty("instance")
public List<InstanceInfo> getInstances() {
  return Optional.ofNullable(shuffledInstances.get()).orElseGet(this::getInstancesAsIsFromEureka);
}

代码示例来源：origin: jenkinsci/jenkins

private static void makeRemovable(@Nonnull Path path) throws IOException {
  if (!Files.isWritable(path)) {
    makeWritable(path);
  }
  /*
   on Unix both the file and the directory that contains it has to be writable
   for a file deletion to be successful. (Confirmed on Solaris 9)
   $ ls -la
   total 6
   dr-xr-sr-x   2 hudson   hudson       512 Apr 18 14:41 .
   dr-xr-sr-x   3 hudson   hudson       512 Apr 17 19:36 ..
   -r--r--r--   1 hudson   hudson       469 Apr 17 19:36 manager.xml
   -rw-r--r--   1 hudson   hudson         0 Apr 18 14:41 x
   $ rm x
   rm: x not removed: Permission denied
   */
  Optional<Path> maybeParent = Optional.ofNullable(path.getParent()).map(Path::normalize).filter(p -> !Files.isWritable(p));
  if (maybeParent.isPresent()) {
    makeWritable(maybeParent.get());
  }
}