title: Flux: filtering exceptions
body: <p>I'm trying to filter exceptions from Flux/ Mono with <code>onErrorContinue</code>, but it never gets triggered.</p>
  
  <pre><code>import org.junit.jupiter.api.Test;
  import reactor.core.publisher.Flux;
  import reactor.test.StepVerifier;
  
  
  class FluxOnErrorContinueTest {
  
      @Test
      public void fluxTest() {
          Flux&lt;String&gt; fluxOne = Flux.just("one")
                  .onErrorContinue(IllegalArgumentException.class, (ex, value) -&gt; System.out.println("fluxOne: " + ex.getMessage()));
          Flux&lt;String&gt; fluxTwo = Flux.&lt;String&gt;error(() -&gt; new IllegalArgumentException("error"))
                  .onErrorContinue(IllegalArgumentException.class, (ex, value) -&gt; System.out.println("fluxTwo: " +ex.getMessage()));
          Flux&lt;String&gt; fluxThree = Flux.just("three", "four", "five")
                  .onErrorContinue(IllegalArgumentException.class, (ex, value) -&gt; System.out.println("fluxThree: " +ex.getMessage()));
  
          Flux&lt;String&gt; sourceFlux = fluxOne.concatWith(fluxTwo).concatWith(fluxThree);
  
          Flux&lt;String&gt; filteredFlux = sourceFlux
                  .onErrorContinue(IllegalArgumentException.class, (ex, value) -&gt; System.out.println("filteredFlux: " + ex.getMessage()));
  
          StepVerifier.create(filteredFlux)
                  .expectNextCount(4)
                  .verifyComplete();
  
      }
  }
  </code></pre>
  
  <p>I would expect to get the four string and a log on the console with the exception message, but I get:</p>
  
  <pre><code>12:15:15.191 [main] DEBUG reactor.util.Loggers$LoggerFactory - Using Slf4j logging framework
  
  java.lang.AssertionError: expectation "expectNextCount(4)" failed (expected: count = 4; actual: counted = 1; signal: onError(java.lang.IllegalArgumentException: error))
  
      at reactor.test.ErrorFormatter.assertionError(ErrorFormatter.java:105)
      at reactor.test.ErrorFormatter.failPrefix(ErrorFormatter.java:94)
      at reactor.test.ErrorFormatter.fail(ErrorFormatter.java:64)
      at reactor.test.ErrorFormatter.failOptional(ErrorFormatter.java:79)
      at reactor.test.DefaultStepVerifierBuilder$DefaultVerifySubscriber.checkCountMismatch(DefaultStepVerifierBuilder.java:1258)
      at reactor.test.DefaultStepVerifierBuilder$DefaultVerifySubscriber.onSignalCount(DefaultStepVerifierBuilder.java:1489)
      at reactor.test.DefaultStepVerifierBuilder$DefaultVerifySubscriber.onExpectation(DefaultStepVerifierBuilder.java:1341)
      at reactor.test.DefaultStepVerifierBuilder$DefaultVerifySubscriber.onError(DefaultStepVerifierBuilder.java:1030)
      at reactor.core.publisher.FluxContextStart$ContextStartSubscriber.onError(FluxContextStart.java:117)
      at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.onError(Operators.java:1748)
      at reactor.core.publisher.Operators.error(Operators.java:181)
      at reactor.core.publisher.FluxErrorSupplied.subscribe(FluxErrorSupplied.java:61)
      at reactor.core.publisher.Flux.subscribe(Flux.java:7921)
      at reactor.core.publisher.FluxConcatArray$ConcatArraySubscriber.onComplete(FluxConcatArray.java:207)
      at reactor.core.publisher.FluxConcatArray.subscribe(FluxConcatArray.java:80)
      at reactor.core.publisher.FluxContextStart.subscribe(FluxContextStart.java:49)
      at reactor.core.publisher.Flux.subscribe(Flux.java:7921)
      at reactor.test.DefaultStepVerifierBuilder$DefaultStepVerifier.verify(DefaultStepVerifierBuilder.java:801)
      at reactor.test.DefaultStepVerifierBuilder$DefaultStepVerifier.verify(DefaultStepVerifierBuilder.java:772)
      at reactor.test.DefaultStepVerifierBuilder.verifyComplete(DefaultStepVerifierBuilder.java:644)
      at com.myorg.FluxOnErrorContinueTest.fluxTest(FluxOnErrorContinueTest.java:21)
      at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
      at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
      at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
      at java.base/java.lang.reflect.Method.invoke(Method.java:566)
      at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:532)
      at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:115)
      at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeTestMethod$6(TestMethodTestDescriptor.java:171)
      at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:72)
      at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeTestMethod(TestMethodTestDescriptor.java:167)
      at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:114)
      at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:59)
      at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$4(NodeTestTask.java:108)
      at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:72)
      at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:98)
      at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:74)
      at java.base/java.util.ArrayList.forEach(ArrayList.java:1540)
      at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38)
      at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$4(NodeTestTask.java:112)
      at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:72)
      at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:98)
      at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:74)
      at java.base/java.util.ArrayList.forEach(ArrayList.java:1540)
      at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38)
      at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$4(NodeTestTask.java:112)
      at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:72)
      at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:98)
      at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:74)
      at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:32)
      at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57)
      at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:51)
      at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:220)
      at org.junit.platform.launcher.core.DefaultLauncher.lambda$execute$6(DefaultLauncher.java:188)
      at org.junit.platform.launcher.core.DefaultLauncher.withInterceptedStreams(DefaultLauncher.java:202)
      at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:181)
      at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:128)
      at com.intellij.junit5.JUnit5IdeaTestRunner.startRunnerWithArgs(JUnit5IdeaTestRunner.java:74)
      at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
      at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
      at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)
      Suppressed: java.lang.IllegalArgumentException: error
          at com.myorg.FluxOnErrorContinueTest.lambda$fluxTest$0(FluxOnErrorContinueTest.java:14)
          at reactor.core.publisher.FluxErrorSupplied.subscribe(FluxErrorSupplied.java:60)
          ... 48 more
  </code></pre>
  
  <p>How can I filter exceptions (try-catch equivalent)?</p>
  
  <p>I also tried with Mono and responses from WebClient.</p>
  
  <p>In the Javadoc "Error Mode Support javadoc section" gets mentioned, but I couldn't find that section. Do you have any links?</p>