CODEWITHSUNDEEP
javaspringjava-streamspring-webfluxreactor
Rocky4Ever
Rocky4Ever

Reputation: 868

Returning Java Object from Mono

I am trying to get Json String from Mono. I tried to use block() method to get object it worked fine , but when I use map/flatmap ,I don't see following lines of code is executed.And I see account Mono is not empty.

private String getJsonString( Mono<Account> account) {
        response.map(it->{
           **// call is not coming here** 
            val json = mapper.writeValueAsString(it)
            System.out.println(son)
        });
    }

am I doing anything wrong here?

Upvotes: 6

Views: 10819

Answers (1)

Abhinaba Chakraborty
Abhinaba Chakraborty

Reputation: 3671

If you give a read to the official documentation , you will see that:

Nothing happens until you subscribe

Now to understand, In spring boot webflux based microservice, who is the subscriber?, have a look at this stackoverflow question

Now, if you think, you can have blocking and reactive implementations in the same service, unfortunately, it doesn't work like that. For this you have to understand the event loop model on which reactor works. Thus calling a block method at any point in the flow is of no good and is equivalent to using the old blocking spring-web methods. Because the thread in which the request is being processed gets blocked and waits for the outcome of the I/O operation / network call.

Coming to your question in the comment:

But when i use flatMap in my controller to call handler method it goes service method with Object not mono?serviceRequest-->Mono-->Object how this works?

Let me give you a simple example for this:

Suppose you have an employee application, where you want to fetch details of an employee for a given id. Now in your controller, you will have an endpoint like this:

@GetMapping("/{tenant}/api/employee/{id}")
  public Mono<ResponseEntity> getEmployeeDetails(@PathVariable("id") Long employeeId) {
    return employeeService.getDetails(employeeId)
        .map(ResponseEntity::ok);
  }

Now in your service,

  public Mono<EmployeeEntity> getDetails(Long employeeId) {
    return employeeRepository.findById(employeeId);
  }

And your repository will look like this:

@Repository
public interface EmployeeRepository extends ReactiveCrudRepository<EmployeeEntity, Long> {

}

Upvotes: 4

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