本文整理了Java中java.util.Optional类的一些代码示例，展示了Optional类的具体用法。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类的具体详情如下：
包路径：java.util.Optional
类名称：Optional

Optional介绍

[英]A container object which may or may not contain a non-null value. If a value is present, isPresent() will return true and get() will return the value.

Additional methods that depend on the presence or absence of a contained value are provided, such as #orElse(java.lang.Object)(return a default value if value not present) and #ifPresent(java.util.function.Consumer) (execute a block of code if the value is present).

This is a value-based class; use of identity-sensitive operations (including reference equality ( ==), identity hash code, or synchronization) on instances of Optional may have unpredictable results and should be avoided.
[中]可以包含或不包含非空值的容器对象。如果存在值，isPresent（）将返回true，get（）将返回该值。
提供了依赖于包含值的存在与否的其他方法，例如#orElse（java.lang.Object）（如果值不存在，则返回默认值）和#ifPresent（java.util.function.Consumer）（如果值存在，则执行代码块）。
这是一个{$0$}类；在Optional实例上使用标识敏感操作（包括引用相等（=）、标识哈希代码或同步）可能会产生不可预测的结果，应避免。

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: prestodb/presto

public boolean hasAllOutputs(TableScanNode node)
{
  if (!layout.getColumns().isPresent()) {
    return true;
  }
  Set<ColumnHandle> columns = ImmutableSet.copyOf(layout.getColumns().get());
  List<ColumnHandle> nodeColumnHandles = node.getOutputSymbols().stream()
      .map(node.getAssignments()::get)
      .collect(toImmutableList());
  return columns.containsAll(nodeColumnHandles);
}

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

@Override
@Nullable
public CorsConfiguration getCorsConfiguration(ServerWebExchange exchange) {
  PathContainer lookupPath = exchange.getRequest().getPath().pathWithinApplication();
  return this.corsConfigurations.entrySet().stream()
      .filter(entry -> entry.getKey().matches(lookupPath))
      .map(Map.Entry::getValue)
      .findFirst()
      .orElse(null);
}

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: stackoverflow.com

void foo(String a, Optional<Integer> bOpt) {
  Integer b = bOpt.isPresent() ? bOpt.get() : 0;
  //...
}

foo("a", Optional.of(2));
foo("a", Optional.<Integer>absent());

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: spring-projects/spring-framework

private String getCharset() {
  return Optional.of(this.bodySpec.returnResult())
      .map(EntityExchangeResult::getResponseHeaders)
      .map(HttpHeaders::getContentType)
      .map(MimeType::getCharset)
      .orElse(StandardCharsets.UTF_8)
      .name();
}

代码示例来源：origin: prestodb/presto

@Override
public synchronized Optional<List<String>> getPartitionNames(String databaseName, String tableName)
{
  return Optional.of(ImmutableList.copyOf(partitions.entrySet().stream()
      .filter(entry -> entry.getKey().matches(databaseName, tableName))
      .map(entry -> entry.getKey().getPartitionName())
      .collect(toList())));
}

代码示例来源：origin: prestodb/presto

public List<Symbol> getOriginalDistinctAggregateArgs()
{
  return aggregations.values().stream()
      .filter(aggregation -> aggregation.getMask().isPresent())
      .map(Aggregation::getCall)
      .flatMap(function -> function.getArguments().stream())
      .distinct()
      .map(Symbol::from)
      .collect(Collectors.toList());
}

代码示例来源：origin: apache/incubator-dubbo

@Override
public synchronized void notify(List<URL> urls) {
  List<URL> categoryUrls = urls.stream()
      .filter(this::isValidCategory)
      .filter(this::isNotCompatibleFor26x)
      .collect(Collectors.toList());
  /**
   * TODO Try to refactor the processing of these three type of urls using Collectors.groupBy()?
   */
  this.configurators = Configurator.toConfigurators(classifyUrls(categoryUrls, UrlUtils::isConfigurator))
      .orElse(configurators);
  toRouters(classifyUrls(categoryUrls, UrlUtils::isRoute)).ifPresent(this::addRouters);
  // providers
  refreshOverrideAndInvoker(classifyUrls(categoryUrls, UrlUtils::isProvider));
}

代码示例来源：origin: prestodb/presto

private synchronized Collection<HivePrivilegeInfo> getTablePrivileges(
    Path permissionsDirectory,
    String principalName,
    PrincipalType principalType)
{
  Path permissionFilePath = getPermissionsPath(permissionsDirectory, principalName, principalType);
  return readFile("permissions", permissionFilePath, permissionsCodec).orElse(ImmutableList.of()).stream()
      .map(PermissionMetadata::toHivePrivilegeInfo)
      .collect(toList());
}

代码示例来源：origin: prestodb/presto

@VisibleForTesting
public Supplier<PageProcessor> createPageProcessor(Page filterTuple, OptionalInt initialBatchSize)
{
  TuplePageFilter filter = new TuplePageFilter(filterTuple, filterTypes, outputFilterChannels);
  return () -> new PageProcessor(
      Optional.of(filter),
      outputProjections.stream()
          .map(Supplier::get)
          .collect(toImmutableList()), initialBatchSize);
}

代码示例来源：origin: prestodb/presto

private Set<NullableValue> filterValues(Set<NullableValue> nullableValues, TpchColumn<?> column, Constraint<ColumnHandle> constraint)
{
  return nullableValues.stream()
      .filter(convertToPredicate(constraint.getSummary(), toColumnHandle(column)))
      .filter(value -> !constraint.predicate().isPresent() || constraint.predicate().get().test(ImmutableMap.of(toColumnHandle(column), value)))
      .collect(toSet());
}

代码示例来源：origin: prestodb/presto

public List<SchemaTableName> listTables(Optional<String> schemaName)
{
  return tableDescriptions.getAllSchemaTableNames()
      .stream()
      .filter(schemaTableName -> !schemaName.isPresent() || schemaTableName.getSchemaName().equals(schemaName.get()))
      .collect(toImmutableList());
}

代码示例来源：origin: prestodb/presto

private static TypeSignature makeSignature(List<Field> fields)
{
  int size = fields.size();
  if (size == 0) {
    throw new IllegalArgumentException("Row type must have at least 1 field");
  }
  List<TypeSignatureParameter> parameters = fields.stream()
      .map(field -> TypeSignatureParameter.of(new NamedTypeSignature(field.getName().map(name -> new RowFieldName(name, false)), field.getType().getTypeSignature())))
      .collect(Collectors.toList());
  return new TypeSignature(ROW, parameters);
}

代码示例来源：origin: prestodb/presto

@JsonCreator
// Available for Jackson deserialization only!
public static <T> TupleDomain<T> fromColumnDomains(@JsonProperty("columnDomains") Optional<List<ColumnDomain<T>>> columnDomains)
{
  if (!columnDomains.isPresent()) {
    return none();
  }
  return withColumnDomains(columnDomains.get().stream()
      .collect(toMap(ColumnDomain::getColumn, ColumnDomain::getDomain)));
}

代码示例来源：origin: prestodb/presto

public Expression toPredicate(TupleDomain<Symbol> tupleDomain)
{
  if (tupleDomain.isNone()) {
    return FALSE_LITERAL;
  }
  Map<Symbol, Domain> domains = tupleDomain.getDomains().get();
  return domains.entrySet().stream()
      .sorted(comparing(entry -> entry.getKey().getName()))
      .map(entry -> toPredicate(entry.getValue(), entry.getKey().toSymbolReference()))
      .collect(collectingAndThen(toImmutableList(), ExpressionUtils::combineConjuncts));
}

代码示例来源：origin: prestodb/presto

private String getPartitionName(String databaseName, String tableName, List<String> partitionValues)
{
  Table table = getTable(databaseName, tableName)
      .orElseThrow(() -> new TableNotFoundException(new SchemaTableName(databaseName, tableName)));
  List<String> columnNames = table.getPartitionColumns().stream()
      .map(Column::getName)
      .collect(toImmutableList());
  return makePartName(columnNames, partitionValues);
}

代码示例来源：origin: prestodb/presto

private static PlanFragment createUnionPlanFragment(String name, PlanFragment... fragments)
{
  PlanNode planNode = new UnionNode(
      new PlanNodeId(name + "_id"),
      Stream.of(fragments)
          .map(fragment -> new RemoteSourceNode(new PlanNodeId(fragment.getId().toString()), fragment.getId(), fragment.getPartitioningScheme().getOutputLayout(), Optional.empty(), REPARTITION))
          .collect(toImmutableList()),
      ImmutableListMultimap.of(),
      ImmutableList.of());
  return createFragment(planNode);
}

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

@ParameterizedTest
@ValueSource(strings = { "Dilbert", "Wally" })
void people(String name, @Autowired List<Person> people) {
  assertTrue(people.stream().map(Person::getName).filter(str -> name.equals(str)).findFirst().isPresent());
}