java.util.NoSuchElementException：即使我们使用流，也没有值

Question

我是 java 的新手，我是运行本地服务器 (jar)，正在尝试访问 API 端点。所有数据都是正确的，我得到以下信息： java.util.NoSuchElementException: 没有值执行似乎发生在代码片段的下面一行 .get()

非常感谢任何帮助！！

使用 java8

final List<BundleValue> existingBundleValues = bundles.stream()
                                                              .filter(bundle -> bundle.type().equals(bundleType))
                                                              .findFirst()
                                                              .get()
                                                              .values()
                                                              .stream()
                                                              .map(BundleValue::convertFromAbstractBundleValue)
                                                              .collect(Collectors.toList());



java.util.NoSuchElementException: No value present
        at java.util.Optional.get(Optional.java:135)
        at com.groupon.goods.productbundlingservice.service.BundlingService.isNewBundle(BundlingService.java:105)
        at com.groupon.goods.productbundlingservice.resources.ProductBundlingServiceResource.createBundle(ProductBundlingServiceResource.java:119)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at org.glassfish.jersey.server.model.internal.ResourceMethodInvocationHandlerFactory.invoke(ResourceMethodInvocationHandlerFactory.java:81)
        at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.run(AbstractJavaResourceMethodDispatcher.java:144)
        at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.invoke(AbstractJavaResourceMethodDispatcher.java:161)
        at org.glassfish.jersey.server.model.internal.JavaResourceMethodDispatcherProvider$ResponseOutInvoker.doDispatch(JavaResourceMethodDispatcherProvider.java:160)
        at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.dispatch(AbstractJavaResourceMethodDispatcher.java:99)
        at org.glassfish.jersey.server.model.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:389)
        at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:347)
        at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:102)
        at org.glassfish.jersey.server.ServerRuntime.run(ServerRuntime.java:326)
        at org.glassfish.jersey.internal.Errors.call(Errors.java:271)
        at org.glassfish.jersey.internal.Errors.call(Errors.java:267)
        at org.glassfish.jersey.internal.Errors.process(Errors.java:315)
        at org.glassfish.jersey.internal.Errors.process(Errors.java:297)
        at org.glassfish.jersey.internal.Errors.process(Errors.java:267)
        at org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:317)
        at org.glassfish.jersey.server.ServerRuntime.process(ServerRuntime.java:305)
        at org.glassfish.jersey.server.ApplicationHandler.handle(ApplicationHandler.java:1154)
        at org.glassfish.jersey.servlet.WebComponent.serviceImpl(WebComponent.java:473)
        at org.glassfish.jersey.servlet.WebComponent.service(WebComponent.java:427)
        at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:388)
        at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:341)
        at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:228)
        at io.dropwizard.jetty.NonblockingServletHolder.handle(NonblockingServletHolder.java:49)
        at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1650)
        at io.dropwizard.servlets.ThreadNameFilter.doFilter(ThreadNameFilter.java:34)
        at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1637)
        at io.dropwizard.jersey.filter.AllowedMethodsFilter.handle(AllowedMethodsFilter.java:45)
        at io.dropwizard.jersey.filter.AllowedMethodsFilter.doFilter(AllowedMethodsFilter.java:39)
        at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1637)
        at com.groupon.jtier.bundles.ctx.CtxFilter.doFilter(CtxFilter.java:56)
        at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1637)
        at com.groupon.jtier.bundles.debug.StenoLoggerFilter.doFilter(StenoLoggerFilter.java:118)
        at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1637)
        at com.groupon.jtier.bundles.debug.RequestServletFilter.doFilter(RequestServletFilter.java:46)
        at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1637)
        at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:533)
        at org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:188)
        at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1253)
        at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:168)
        at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:473)
        at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:166)
        at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1155)
        at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:141)
        at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:132)
        at com.codahale.metrics.jetty9.InstrumentedHandler.handle(InstrumentedHandler.java:241)
        at io.dropwizard.jetty.RoutingHandler.handle(RoutingHandler.java:52)
        at org.eclipse.jetty.server.handler.gzip.GzipHandler.handle(GzipHandler.java:455)
        at io.dropwizard.jetty.BiDiGzipHandler.handle(BiDiGzipHandler.java:68)
        at org.eclipse.jetty.server.handler.StatisticsHandler.handle(StatisticsHandler.java:169)
        at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:132)
        at org.eclipse.jetty.server.Server.handle(Server.java:561)
        at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:334)
        at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:251)
        at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:279)
        at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:104)
        at org.eclipse.jetty.io.ChannelEndPoint.run(ChannelEndPoint.java:124)
        at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:679)
        at org.eclipse.jetty.util.thread.QueuedThreadPool.run(QueuedThreadPool.java:597)
        at java.lang.Thread.run(Thread.java:748)

Answer 1

firstFirst returns 一个 Optional，你调用 get，如果它是一个 empty 可选 - 你会得到那个异常。

您可以按如下方式编写它，如果它存在（Optional），您会将其映射到 Map::values（我假设您的 findFirst returns某种 Map)，否则得到 Collections.emptyList().

bundles.stream()
       .filter(bundle -> bundle.type().equals(bundleType))
       .findFirst()
       .map(Map::values)
       .orElse(Collections.emptyList())
       .stream()
       .map(BundleValue::convertFromAbstractBundleValue)
       .collect(Collectors.toList());

Answer 2

Optional#get() 如果没有值则抛出 NoSuchElementException 表示值为 null。

为避免异常，您可以使用 Optional#orElse(T other) 其中 returns 值（如果存在），否则 returns other 方法中传递的值。

Optional<Integer> d1  =  Optional.of(10);
Optional<Integer> d2  =  Optional.empty();
Integer res1 = d1.orElse(0);  // return 10 since value is present
Integer res2 = d2.orElse(0);  // return 0 since value is not present

或者您想在没有值时抛出异常，然后使用 orElseThrow

optionalObj.orElseThrow(ArithmeticException::new)

然后就可以根据值做进一步的操作了

java.util.NoSuchElementException：即使我们使用流，也没有值

java.util.NoSuchElementException: No value present even though we use stream

filter

java-8

java-stream

optional

nosuchelementexception