{"id":130164,"date":"2025-01-14T18:44:00","date_gmt":"2025-01-14T16:44:00","guid":{"rendered":"https:\/\/www.javacodegeeks.com\/?p=130164"},"modified":"2025-01-13T10:56:35","modified_gmt":"2025-01-13T08:56:35","slug":"reactive-mono-just-defer-create-example","status":"publish","type":"post","link":"https:\/\/www.javacodegeeks.com\/reactive-mono-just-defer-create-example.html","title":{"rendered":"Reactive Mono just(), defer(), create() Example"},"content":{"rendered":"

Reactive Programming is a programming paradigm that allows developers to build asynchronous, non-blocking, and event-driven applications. In the Project Reactor library, Mono<\/code> represents a single asynchronous value (either present or empty). Let us delve into understanding how reactive Mono works, and how we can use methods like just(), defer() and create() to manage asynchronous data flows.<\/p>\n

<\/a>1. Mono.just()<\/h2>\n

The Mono.just()<\/code> method is used to create a Mono<\/code> that emits a specific value. It is straightforward and emits the value immediately upon subscription. This method is particularly useful when you have a known value or a constant that you want to expose as a reactive stream. When you use Mono.just()<\/code>, the provided value is stored and emitted to all subscribers. It’s important to note that this method does not execute any lazy or deferred logic; the value is prepared and ready to be emitted as soon as a subscriber subscribes to the Mono<\/code>. This makes it efficient for static or precomputed values, but less suitable for values that need to be computed or fetched on demand.<\/p>\n

1.1 Example<\/h3>\n

Here is an example demonstrating the use of the Mono.just()<\/code> method:<\/p>\n

import reactor.core.publisher.Mono;\n\npublic class MonoJustExample {\n    public static void main(String[] args) {\n        Mono<String> monoJust = Mono.just(\"Hello, World!\");\n        monoJust.subscribe(System.out::println);\n    }\n}\n<\/pre>\n
In this example, Mono.just(\"Hello, World!\")<\/code> creates a Mono<\/code> that emits the string “Hello, World!”. When the subscribe()<\/code> method is called, the value is printed to the console.<\/p>\n
Hello, World!\n<\/pre>\n
1.2 Use cases<\/h3>\n
The method serves the following purposes:<\/p>\n