Spring Webflux: Do I need to catch(Throwable) for triggering Mono.doOnError?

Question

I have the following Code that creates a product and then logs the creation-success in some kind of history service (the journalClient).

If there is an error in the journal client I want to rollback the product creation.

@Service
public class ProductService {

    public Mono<ProductRS> createProduct(final ProductRQ rq) {
       return productclient.createProduct(rq).flatMap(produktfamilieRS -> {
         return journalClient.createJournalEntry("Dummy-Entry").thenReturn(productRS)
             .doOnError(throwable -> {
                 log.error("Error creating journal Entry - Starting rollback of transaction.");
                 rollbackCreateProduct(productRS.getId());
          });
    });

    private void rollbackCreateProduktfamilie(long id) {
       productClient.deleteProduct(id).subscribe();
    }

@Service
public class JournalClientMockImpl implements JournalClientMock {

  public Mono<Void> createJournalEntry(String body, boolean error) {
    throw new RuntimeExcpeption("Test Error");
  }

My problem is, that the RuntimeException that I throw in the JournalClient does not trigger the Mono.doOnError() in the ProductService.createProduct.

Sticking Point: I found out that returning an Mono.error triggers the outer doOnError:

@Service
public class JournalClientMockImpl implements JournalClientMock {

  public Mono<Void> createJournalEntry(String body, boolean error) {
      return Mono.error(new RuntimeException("Beabsichtiger Fehler im JournalServiceMock"));
  }

But my problem with that is, that there could be errors in my business logic that cause RuntimeExceptions that will not end in a Mono.error.

My bad idea: The only idea I have is to do something like this....surrounding the whole code with a catch-all:

  public Mono<Void> createJournalEntry(String body, boolean error) {
    try{
      // do some business logic
      // ...
      // call journal web service
      // ...
      return Mono.empty();
    } catch (Throwable e){
      return Mono.error(new RuntimeException("Error in JournalServiceMock"));
    }
   
  }

Should this be the solution? This smells like very bad design. How to do this properly?

Thank you very much

Do on error is for side effects only, like logging etc. If you wish to switch to another publisher you should use for instance onErrorResume. — Toerktumlare, Jul 14 '21 at 16:39

score 1 · Answer 1 · answered Jul 16 '21 at 07:20

Try .onErrorResume instead of .doOnError

@Service
public class ProductService {

    public Mono<ProductRS> createProduct(final ProductRQ rq) {
       return productclient.createProduct(rq).flatMap(produktfamilieRS -> {
         return journalClient.createJournalEntry("Dummy-Entry").thenReturn(productRS)
             .onErrorResume(throwable -> {
                 log.error("Error creating journal Entry - Starting rollback of transaction.");
                 rollbackCreateProduct(productRS.getId());
          });
    });

    private void rollbackCreateProduktfamilie(long id) {
       productClient.deleteProduct(id).subscribe();
    }

Spring Webflux: Do I need to catch(Throwable) for triggering Mono.doOnError?

1 Answers1