Как выловить java util nosuchelementexception

Как выловить java util nosuchelementexception

Constructs a NoSuchElementException , saving a reference to the error message string s for later retrieval by the getMessage method.

Method Summary

Methods inherited from class java.lang.Throwable

Methods inherited from class java.lang.Object

Constructor Detail

NoSuchElementException

public NoSuchElementException()

Constructs a NoSuchElementException with null as its error message string.

NoSuchElementException

Constructs a NoSuchElementException , saving a reference to the error message string s for later retrieval by the getMessage method.

Java™ Platform
Standard Ed. 8

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For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
Copyright © 1993, 2023, Oracle and/or its affiliates. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.

How to solve java.util.NoSuchElementException in this code?

Try to use if(sc.hasNextLine()) before actually trying to read the next line. JavaDoc on hasNextLine() : «This method may block while waiting for input.».

Oct 13, 2022 at 6:52

1 Answer 1

At least something like this can be done:

String name = ""; if (sc.hasNextLine())

Or even better you can use optionals not to have empty line.

answered Oct 13, 2022 at 6:54
1 2 2 bronze badges

• java
• java.util.scanner
• nosuchelementexception

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Как выловить java util nosuchelementexception

Constructs a NoSuchElementException , saving a reference to the error message string s for later retrieval by the getMessage method.

Method Summary

Methods declared in class java.lang.Throwable

Methods declared in class java.lang.Object

Constructor Detail

NoSuchElementException

public NoSuchElementException()

Constructs a NoSuchElementException with null as its error message string.

NoSuchElementException

Constructs a NoSuchElementException , saving a reference to the error message string s for later retrieval by the getMessage method.

Report a bug or suggest an enhancement
For further API reference and developer documentation see the Java SE Documentation, which contains more detailed, developer-targeted descriptions with conceptual overviews, definitions of terms, workarounds, and working code examples.
Java is a trademark or registered trademark of Oracle and/or its affiliates in the US and other countries.
Copyright © 1993, 2023, Oracle and/or its affiliates, 500 Oracle Parkway, Redwood Shores, CA 94065 USA.
All rights reserved. Use is subject to license terms and the documentation redistribution policy.

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When using instrumented Maybe — getting java.util.NoSuchElementException #3265

philippreston opened this issue May 18, 2020 · 0 comments

When using instrumented Maybe — getting java.util.NoSuchElementException #3265

philippreston opened this issue May 18, 2020 · 0 comments
type: bug Something isn’t working

Comments

Contributor
philippreston commented May 18, 2020

Task List

• Steps to reproduce provided
• Stacktrace (if present) provided
• Example that reproduces the problem uploaded to Github
• Full description of the issue provided (see below)

Steps to Reproduce

1. Add @NewSpan to a method that returns a Maybe from a method that returns a Publisher

Expected Behaviour

That a Maybe that wraps a Publisher which emits 0 items, returns an empty Maybe.

Actual Behaviour

The actual behaviour is that we get an exception:

Caused by: java.util.NoSuchElementException: The source Publisher is empty at io.reactivex.internal.operators.single.SingleFromPublisher$ToSingleObserver.onComplete(SingleFromPublisher.java:99) at io.micronaut.tracing.instrument.util.TracingPublisher$1.onComplete(TracingPublisher.java:182) at io.reactivex.internal.util.HalfSerializer.onComplete(HalfSerializer.java:90) at io.reactivex.internal.subscribers.StrictSubscriber.onComplete(StrictSubscriber.java:109) at io.reactivex.internal.operators.flowable.FlowableElementAt$ElementAtSubscriber.onComplete(FlowableElementAt.java:105) at io.reactivex.internal.operators.flowable.FlowableDoOnEach$DoOnEachSubscriber.onComplete(FlowableDoOnEach.java:135) at io.reactivex.internal.operators.flowable.FlowableDoOnLifecycle$SubscriptionLambdaSubscriber.onComplete(FlowableDoOnLifecycle.java:94) at io.reactivex.internal.operators.flowable.FlowableDoOnEach$DoOnEachSubscriber.onComplete(FlowableDoOnEach.java:135) at io.reactivex.internal.operators.flowable.FlowableDoOnEach$DoOnEachSubscriber.onComplete(FlowableDoOnEach.java:135) at com.mongodb.reactivestreams.client.internal.ObservableToPublisher$1.onComplete(ObservableToPublisher.java:76) at com.mongodb.async.client.AbstractSubscription.onComplete(AbstractSubscription.java:154) at com.mongodb.async.client.AbstractSubscription.processResultsQueue(AbstractSubscription.java:225) at com.mongodb.async.client.AbstractSubscription.tryProcessResultsQueue(AbstractSubscription.java:172) at com.mongodb.async.client.MongoIterableSubscription$2.onResult(MongoIterableSubscription.java:105) at com.mongodb.async.client.MongoIterableSubscription$2.onResult(MongoIterableSubscription.java:89) at com.mongodb.operation.AsyncQueryBatchCursor.next(AsyncQueryBatchCursor.java:174) at com.mongodb.operation.AsyncQueryBatchCursor.next(AsyncQueryBatchCursor.java:118) at com.mongodb.async.client.MongoIterableSubscription.requestMoreData(MongoIterableSubscription.java:89) at com.mongodb.async.client.MongoIterableSubscription$1.onResult(MongoIterableSubscription.java:53) at com.mongodb.async.client.MongoIterableSubscription$1.onResult(MongoIterableSubscription.java:46) at com.mongodb.internal.async.ErrorHandlingResultCallback.onResult(ErrorHandlingResultCallback.java:49) at com.mongodb.async.client.OperationExecutorImpl$1$1$1.onResult(OperationExecutorImpl.java:94) at com.mongodb.internal.async.ErrorHandlingResultCallback.onResult(ErrorHandlingResultCallback.java:49) at com.mongodb.operation.FindOperation$3.onResult(FindOperation.java:827) at com.mongodb.operation.OperationHelper$ReferenceCountedReleasingWrappedCallback.onResult(OperationHelper.java:412) at com.mongodb.operation.CommandOperationHelper$10.onResult(CommandOperationHelper.java:481) at com.mongodb.internal.async.ErrorHandlingResultCallback.onResult(ErrorHandlingResultCallback.java:49) at com.mongodb.internal.connection.DefaultServer$DefaultServerProtocolExecutor$2.onResult(DefaultServer.java:253) at com.mongodb.internal.async.ErrorHandlingResultCallback.onResult(ErrorHandlingResultCallback.java:49) at com.mongodb.internal.connection.CommandProtocolImpl$1.onResult(CommandProtocolImpl.java:85) at com.mongodb.internal.connection.DefaultConnectionPool$PooledConnection$1.onResult(DefaultConnectionPool.java:467) at com.mongodb.internal.connection.UsageTrackingInternalConnection$2.onResult(UsageTrackingInternalConnection.java:111) at com.mongodb.internal.async.ErrorHandlingResultCallback.onResult(ErrorHandlingResultCallback.java:49) at com.mongodb.internal.connection.InternalStreamConnection$2$1.onResult(InternalStreamConnection.java:399) at com.mongodb.internal.connection.InternalStreamConnection$2$1.onResult(InternalStreamConnection.java:376) at com.mongodb.internal.connection.InternalStreamConnection$MessageHeaderCallback$MessageCallback.onResult(InternalStreamConnection.java:677) at com.mongodb.internal.connection.InternalStreamConnection$MessageHeaderCallback$MessageCallback.onResult(InternalStreamConnection.java:644) at com.mongodb.internal.connection.InternalStreamConnection$5.completed(InternalStreamConnection.java:514) at com.mongodb.internal.connection.InternalStreamConnection$5.completed(InternalStreamConnection.java:511) at com.mongodb.internal.connection.AsynchronousChannelStream$BasicCompletionHandler.completed(AsynchronousChannelStream.java:220) at com.mongodb.internal.connection.AsynchronousChannelStream$BasicCompletionHandler.completed(AsynchronousChannelStream.java:203) at java.base/sun.nio.ch.Invoker.invokeUnchecked(Invoker.java:127) at java.base/sun.nio.ch.Invoker.invokeDirect(Invoker.java:158) at java.base/sun.nio.ch.UnixAsynchronousSocketChannelImpl.implRead(UnixAsynchronousSocketChannelImpl.java:560) at java.base/sun.nio.ch.AsynchronousSocketChannelImpl.read(AsynchronousSocketChannelImpl.java:277) at java.base/sun.nio.ch.AsynchronousSocketChannelImpl.read(AsynchronousSocketChannelImpl.java:298) at com.mongodb.internal.connection.AsynchronousSocketChannelStream$AsynchronousSocketChannelAdapter.read(AsynchronousSocketChannelStream.java:137) at com.mongodb.internal.connection.AsynchronousChannelStream.readAsync(AsynchronousChannelStream.java:105) at com.mongodb.internal.connection.InternalStreamConnection.readAsync(InternalStreamConnection.java:511) at com.mongodb.internal.connection.InternalStreamConnection.access$1000(InternalStreamConnection.java:76) at com.mongodb.internal.connection.InternalStreamConnection$MessageHeaderCallback.onResult(InternalStreamConnection.java:634) at com.mongodb.internal.connection.InternalStreamConnection$MessageHeaderCallback.onResult(InternalStreamConnection.java:619) at com.mongodb.internal.connection.InternalStreamConnection$5.completed(InternalStreamConnection.java:514) at com.mongodb.internal.connection.InternalStreamConnection$5.completed(InternalStreamConnection.java:511) at com.mongodb.internal.connection.AsynchronousChannelStream$BasicCompletionHandler.completed(AsynchronousChannelStream.java:220) at com.mongodb.internal.connection.AsynchronousChannelStream$BasicCompletionHandler.completed(AsynchronousChannelStream.java:203) at java.base/sun.nio.ch.Invoker.invokeUnchecked(Invoker.java:127) at java.base/sun.nio.ch.UnixAsynchronousSocketChannelImpl.finishRead(UnixAsynchronousSocketChannelImpl.java:437) at java.base/sun.nio.ch.UnixAsynchronousSocketChannelImpl.finish(UnixAsynchronousSocketChannelImpl.java:191) at java.base/sun.nio.ch.UnixAsynchronousSocketChannelImpl.onEvent(UnixAsynchronousSocketChannelImpl.java:213) at java.base/sun.nio.ch.KQueuePort$EventHandlerTask.run(KQueuePort.java:312) at java.base/sun.nio.ch.AsynchronousChannelGroupImpl$1.run(AsynchronousChannelGroupImpl.java:112) at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) at java.base/java.lang.Thread.run(Thread.java:834) 

The use case we have is using the reactive Mongo library. When doing a find — and no results are returned, the Publisher completes without emitting an item. Our method looks like:

public MaybeRole> findById(String id) < return Flowable.fromPublisher(collection().find(eq("_id", new ObjectId(id)))) .firstElement(); >

 @NewSpan Maybe findById(String id); 

The stack trace shows that in the Publisher to Maybe conversion — the Publisher is being wrapped by a Single which does not allow for empty, hence the exception.