NullPointerException when followOutput() called before start()

[findepi]

container.followOutput(new Slf4jLogConsumer(org.slf4j.LoggerFactory.getLogger("...")));
container.start();

Observed

Exception in thread "main" java.lang.NullPointerException: containerId was not specified
	at org.testcontainers.shaded.com.google.common.base.Preconditions.checkNotNull(Preconditions.java:228)
	at com.github.dockerjava.core.command.LogContainerCmdImpl.withContainerId(LogContainerCmdImpl.java:78)
	at com.github.dockerjava.core.command.LogContainerCmdImpl.<init>(LogContainerCmdImpl.java:38)
	at com.github.dockerjava.core.DockerClientImpl.logContainerCmd(DockerClientImpl.java:364)
	at org.testcontainers.dockerclient.AuditLoggingDockerClient.logContainerCmd(AuditLoggingDockerClient.java:23)
	at org.testcontainers.utility.LogUtils.attachConsumer(LogUtils.java:88)
	at org.testcontainers.utility.LogUtils.followOutput(LogUtils.java:36)
	at org.testcontainers.utility.LogUtils.followOutput(LogUtils.java:51)
	at org.testcontainers.containers.Container.followOutput(Container.java:391)

Expected

followOutput should accept the log consumer before start() is called.
start() is blocking, so calling followOutput seems like the right way to install the log consumer so it can get logs during startup phase too.

[bsideup]

I think the exception's message is self explanatory. You cannot get the logs of a non-started container.

If you want to provide a consumer at setup time, use withLogConsumer.

[findepi]

Thanks for the advice.

BTW message is explanatory enough to convey "this doesn't work".
to me, if it was an IllegalStateException, it would also convey "this intentionally doesn't work".

[yeroc]

This messed me up as well. I wonder if it would be worth splitting the setup methods into a separate Builder-style API so the setup functions are separated from the runtime methods?

[bsideup]

@yeroc
We're working on it :) In fact, last month we had a very productive hackathon with @rnorth where we prototyped such API. Stay tuned!

[yeroc]

@bsideup Awesome! Look forward to seeing it. Regards, Corey

[renannprado]

@bsideup is the API now available...? I'm in the same situation.

@findepi did you find a solution?

[sebialex]

I think the exception's message is self explanatory. You cannot get the logs of a non-started container.

If you want to provide a consumer at setup time, use withLogConsumer.

This should be handled by the builder pattern, there would be no followOutput on a builder, but the withLogConsumer would, leaving followOutput to only be available to the built instance. No confusion.

[FelixZY]

I found this issue after having the same issue myself. The solution is fairly obvious in hindsight but maybe the docs at https://java.testcontainers.org/features/container_logs/#streaming-container-output-to-an-slf4j-logger could be made a little clearer?

[whiskeysierra]

I think the exception's message is self explanatory. You cannot get the logs of a non-started container.

That is not what the message says though.
It might be obvious to everyone who makes the immediate connection from a missing containerId to the state of the container, but that is neither immediately clear nor self explanatory.