How to handle exceptions in reactive code?

In reactive programming (for example, using Project Reactor or RxJava), error handling differs from the traditional approach. Instead of try-catch, a special operator is used to handle errors in the data stream.

Main error handling methods:

• onErrorReturn — returns a fallback value when an error occurs.
• onErrorResume — switches to another stream upon an error.
• retry — repeats the subscription a specified number of times upon an error.
• doOnError — allows performing side effects when an error occurs (logging, etc.).

Example in Reactor:

Flux.just(1, 2, 0, 4)
    .map(i -> 10 / i) // ArithmeticException when i=0
    .onErrorResume(e -> Flux.just(-1)) // return a stream with -1 on error
    .subscribe(System.out::println);

Thus, errors are not thrown outward but are handled within the reactive stream, which allows maintaining asynchrony and continuous data processing.