java.util.Optional.empty()方法的使用及代码示例

x33g5p2x  于2022-01-17 转载在 其他  
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本文整理了Java中java.util.Optional.empty()方法的一些代码示例，展示了Optional.empty()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.empty()方法的具体详情如下：
包路径：java.util.Optional
类名称：Optional
方法名：empty

Optional.empty介绍

暂无

代码示例

代码示例来源：origin: prestodb/presto

public Optional<Scope> getOuterQueryParent()
{
  Scope scope = this;
  while (scope.parent.isPresent()) {
    if (scope.queryBoundary) {
      return scope.parent;
    }
    scope = scope.parent.get();
  }
  return Optional.empty();
}

代码示例来源：origin: prestodb/presto

private static Optional<List<Symbol>> translateSymbols(Iterable<Symbol> partitioning, Function<Symbol, Optional<Symbol>> translator)
{
  ImmutableList.Builder<Symbol> newPartitioningColumns = ImmutableList.builder();
  for (Symbol partitioningColumn : partitioning) {
    Optional<Symbol> translated = translator.apply(partitioningColumn);
    if (!translated.isPresent()) {
      return Optional.empty();
    }
    newPartitioningColumns.add(translated.get());
  }
  return Optional.of(newPartitioningColumns.build());
}

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

/**
 * Transform the given request into a request used for a nested route. For instance,
 * a path-based predicate can return a {@code ServerRequest} with a the path remaining
 * after a match.
 * <p>The default implementation returns an {@code Optional} wrapping the given path if
 * {@link #test(ServerRequest)} evaluates to {@code true}; or {@link Optional#empty()}
 * if it evaluates to {@code false}.
 * @param request the request to be nested
 * @return the nested request
 * @see RouterFunctions#nest(RequestPredicate, RouterFunction)
 */
default Optional<ServerRequest> nest(ServerRequest request) {
  return (test(request) ? Optional.of(request) : Optional.empty());
}

代码示例来源：origin: SonarSource/sonarqube

private static Optional<String> getParameter(HttpServletRequest request, String parameterKey) {
 Optional<javax.servlet.http.Cookie> cookie = findCookie(AUTHENTICATION_COOKIE_NAME, request);
 if (!cookie.isPresent()) {
  return empty();
 }
 Map<String, String> parameters = fromJson(cookie.get().getValue());
 if (parameters.isEmpty()) {
  return empty();
 }
 return Optional.ofNullable(parameters.get(parameterKey));
}

代码示例来源：origin: prestodb/presto

@Test
public void testCreateTableAsSelectDifferentCatalog()
    throws Exception
{
  handle.execute("CREATE TABLE \"my_test_table2\" (column1 BIGINT, column2 DOUBLE)");
  SqlParser parser = new SqlParser();
  Query query = new Query(CATALOG, SCHEMA, ImmutableList.of(), "CREATE TABLE public.my_test_table2 AS SELECT 1 column1, 2E0 column2", ImmutableList.of(), null, null, ImmutableMap.of());
  QueryRewriter rewriter = new QueryRewriter(parser, URL, QualifiedName.of("other_catalog", "other_schema", "tmp_"), Optional.empty(), Optional.empty(), Optional.empty(), Optional.empty(), 1, new Duration(10, SECONDS));
  Query rewrittenQuery = rewriter.shadowQuery(query);
  assertEquals(rewrittenQuery.getPreQueries().size(), 1);
  CreateTableAsSelect createTableAs = (CreateTableAsSelect) parser.createStatement(rewrittenQuery.getPreQueries().get(0));
  assertEquals(createTableAs.getName().getParts().size(), 3);
  assertEquals(createTableAs.getName().getPrefix().get(), QualifiedName.of("other_catalog", "other_schema"));
  assertTrue(createTableAs.getName().getSuffix().startsWith("tmp_"));
  assertFalse(createTableAs.getName().getSuffix().contains("my_test_table"));
}

代码示例来源：origin: prestodb/presto

private static LdapObjectDefinition buildLdapGroupObject(String groupName, String userName, Optional<List<String>> childGroupNames)
{
  if (childGroupNames.isPresent()) {
    return buildLdapGroupObject(groupName, AMERICA_DISTINGUISHED_NAME, userName, ASIA_DISTINGUISHED_NAME, childGroupNames, Optional.of(AMERICA_DISTINGUISHED_NAME));
  }
  else {
    return buildLdapGroupObject(groupName, AMERICA_DISTINGUISHED_NAME, userName, ASIA_DISTINGUISHED_NAME,
        Optional.empty(), Optional.empty());
  }
}

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

@Test
@SuppressWarnings("rawtypes")
public void resolveOptionalParamList() throws Exception {
  ConfigurableWebBindingInitializer initializer = new ConfigurableWebBindingInitializer();
  initializer.setConversionService(new DefaultConversionService());
  WebDataBinderFactory binderFactory = new DefaultDataBinderFactory(initializer);
  MethodParameter param = this.testMethod.annotPresent(RequestParam.class).arg(Optional.class, List.class);
  Object result = resolver.resolveArgument(param, null, webRequest, binderFactory);
  assertEquals(Optional.empty(), result);
  request.addParameter("name", "123", "456");
  result = resolver.resolveArgument(param, null, webRequest, binderFactory);
  assertEquals(Optional.class, result.getClass());
  assertEquals(Arrays.asList("123", "456"), ((Optional) result).get());
}

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

@Test
@SuppressWarnings("unchecked")
public void attributesAsOptionalEmpty() throws Exception {
  request.addParameter("name", "Patty");
  mavContainer.getModel().put("testBean1", Optional.empty());
  mavContainer.getModel().put("testBean2", Optional.empty());
  mavContainer.getModel().put("testBean3", Optional.empty());
  assertNull(processor.resolveArgument(
      testBeanModelAttr, mavContainer, webRequest, binderFactory));
  assertNull(processor.resolveArgument(
      testBeanWithoutStringConstructorModelAttr, mavContainer, webRequest, binderFactory));
  Optional<TestBean> testBean =(Optional<TestBean>) processor.resolveArgument(
      testBeanWithOptionalModelAttr, mavContainer, webRequest, binderFactory);
  assertFalse(testBean.isPresent());
}

代码示例来源：origin: apache/incubator-dubbo

private static Optional<InetAddress> toValidAddress(InetAddress address) {
  if (address instanceof Inet6Address) {
    Inet6Address v6Address = (Inet6Address) address;
    if (isValidV6Address(v6Address)) {
      return Optional.ofNullable(normalizeV6Address(v6Address));
    }
  }
  if (isValidV4Address(address)) {
    return Optional.of(address);
  }
  return Optional.empty();
}

代码示例来源：origin: neo4j/neo4j

@Test
void handlesDeprecationAndReplacement()
{
  ConfigValue value = new ConfigValue( "old_name", Optional.empty(), Optional.empty(), Optional.of( 1 ),
      "description", false, false, true, Optional.of( "new_name" ), false );
  assertEquals( Optional.of( 1 ), value.value() );
  assertEquals( "1", value.toString() );
  assertTrue( value.deprecated() );
  assertEquals( "new_name", value.replacement().get() );
  assertFalse( value.internal() );
  assertFalse( value.secret() );
}

代码示例来源：origin: prestodb/presto

public Optional<WithQuery> getNamedQuery(String name)
{
  if (namedQueries.containsKey(name)) {
    return Optional.of(namedQueries.get(name));
  }
  if (parent.isPresent()) {
    return parent.get().getNamedQuery(name);
  }
  return Optional.empty();
}

代码示例来源：origin: prestodb/presto

@Override
public void finishMemoryRevoke()
{
  checkState(finishMemoryRevoke.isPresent(), "Cannot finish unknown revoking");
  finishMemoryRevoke.get().run();
  finishMemoryRevoke = Optional.empty();
}

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

/**
 * Can be used to collect objects from the Iterable. Is a terminating operation.
 * 
 * @return an option of the first object of the Iterable
 */
@Override
public final Optional<E> first() {
 Iterator<E> resultIterator = first(1).iterator();
 return resultIterator.hasNext() ? Optional.of(resultIterator.next()) : Optional.empty();
}

代码示例来源：origin: prestodb/presto

private static LdapObjectDefinition buildLdapUserObject(String userName, Optional<List<String>> groupNames, String password)
{
  if (groupNames.isPresent()) {
    return buildLdapUserObject(userName, ASIA_DISTINGUISHED_NAME,
        groupNames, Optional.of(AMERICA_DISTINGUISHED_NAME), password);
  }
  else {
    return buildLdapUserObject(userName, ASIA_DISTINGUISHED_NAME,
        Optional.empty(), Optional.empty(), password);
  }
}

代码示例来源：origin: prestodb/presto

private Session getSession(String user)
  {
    return testSessionBuilder()
        .setCatalog(queryRunner.getDefaultSession().getCatalog().get())
        .setSchema(queryRunner.getDefaultSession().getSchema().get())
        .setIdentity(new Identity(user, Optional.empty())).build();
  }
}

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

@Test
@SuppressWarnings("rawtypes")
public void missingOptionalParamValue() throws Exception {
  ConfigurableWebBindingInitializer initializer = new ConfigurableWebBindingInitializer();
  initializer.setConversionService(new DefaultConversionService());
  WebDataBinderFactory binderFactory = new DefaultDataBinderFactory(initializer);
  MethodParameter param = this.testMethod.annotPresent(RequestParam.class).arg(Optional.class, Integer.class);
  Object result = resolver.resolveArgument(param, null, webRequest, binderFactory);
  assertEquals(Optional.empty(), result);
  result = resolver.resolveArgument(param, null, webRequest, binderFactory);
  assertEquals(Optional.class, result.getClass());
  assertFalse(((Optional) result).isPresent());
}

代码示例来源：origin: apache/incubator-dubbo

private static Optional<InetAddress> toValidAddress(InetAddress address) {
  if (address instanceof Inet6Address) {
    Inet6Address v6Address = (Inet6Address) address;
    if (isValidV6Address(v6Address)) {
      return Optional.ofNullable(normalizeV6Address(v6Address));
    }
  }
  if (isValidV4Address(address)) {
    return Optional.of(address);
  }
  return Optional.empty();
}

代码示例来源：origin: prestodb/presto

private Optional<Symbol> canonicalize(Optional<Symbol> symbol)
{
  if (symbol.isPresent()) {
    return Optional.of(canonicalize(symbol.get()));
  }
  return Optional.empty();
}

代码示例来源：origin: prestodb/presto

public Optional<HashComputation> translate(Function<Symbol, Optional<Symbol>> translator)
{
  ImmutableList.Builder<Symbol> newSymbols = ImmutableList.builder();
  for (Symbol field : fields) {
    Optional<Symbol> newSymbol = translator.apply(field);
    if (!newSymbol.isPresent()) {
      return Optional.empty();
    }
    newSymbols.add(newSymbol.get());
  }
  return computeHash(newSymbols.build());
}

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

/**
 * Can be used to collect objects from the Iterable. Is a terminating operation.
 * 
 * @return an option of the last object of the Iterable
 */
@Override
public final Optional<E> last() {
 List<E> list = last(1).asList();
 if (list.isEmpty()) {
  return Optional.empty();
 }
 return Optional.of(list.get(0));
}

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