How to read file lines while they appear and represent them as Flux?

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Assume we depend on Reactor 3 (i.e in a Spring 5 application) and a text file my/file.txt.

I need to subscribe to the text file lines (both existing ones and those that will appear in the future) and create a Flux<String>. If you wish, neglect blocking IO reads concerns, let's just reveal the principle of building such subscription.

For simplicity assume that we print those lines to std output:

flowLinesFrom(Path.of("my/file.txt"))
   .subscribe(System.out::println);

What is the proper way to implement Flux<String> flowLinesFrom(Path)?

spring-reactor flux project-reactor java
1 Answers

You can use this like so

//Create FluxTailer
FluxTailer tailer = new FluxTailer(
    //The file to tail
    Path.of("my/file.txt").toFile(),
    //Polling interval for changes
    Duration.ofSeconds(1)
);

//Start tailing
tailer.start();

//Subscribe to the tailer flux
tailer.flux().subscribe(System.out::println);

//Just for demo you wait for 10 seconds
try{
    Thread.sleep(10000);
}catch (Exception e){}

//Stop the tailer when done, will also complete the flux
tailer.stop();

You can start stop as you please and also set to read from start or end of file using

tailer.readFromStart();
tailer.readFromEnd();
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