Inspectopedia Help

Unused publisher

Reports unused Publisher instances.

To use an operator (a method of Mono/Flux/Flowable object that returns a Mono/Flux/Flowable) that produces a new Publisher instance, you must subscribe to the created Publisher via subscribe().

Using a factory (for example, Mono.just()) without subscribing to the returned Publisher, creates an object that is never used and is treated as unnecessary memory allocation.

For example, Mono.just(1, 2, 3).map(i -> i + 3) won't be executed unless you subscribe to this Publisher, or unless you produce a new Publisher by applying operators and subscribe to it.


Unused Flux instance:

Flux.just(1, 2, 3);

A Flux instance used by consumer:

Flux.just(1, 2, 3).subscribe(System.out::println);

Calls to methods annotated with Error Prone's or AssertJ's @CanIgnoreReturnValue annotation are not reported.

Locating this inspection


Can be used to locate inspection in e.g. Qodana configuration files, where you can quickly enable or disable it, or adjust its settings.

Via Settings dialog

Path to the inspection settings via IntelliJ Platform IDE Settings dialog, when you need to adjust inspection settings directly from your IDE.

Settings or Preferences | Editor | Inspections | Reactive Streams | Common

New in 2019.3


By default bundled with

IntelliJ IDEA 2024.1, Qodana for JVM 2024.1,

Can be installed with plugin

Reactive Streams, 241.18072

Last modified: 18 June 2024