Pick status code from ErrorResponse interfaces

problem-spring-common/src/main/java/org/zalando/problem/spring/common/AdviceTrait.java

@@ -1,7 +1,9 @@
 package org.zalando.problem.spring.common;
 
 import org.apiguardian.api.API;
+import org.springframework.http.HttpStatusCode;
 import org.springframework.http.ResponseEntity;
+import org.springframework.web.ErrorResponse;
 import org.springframework.web.bind.annotation.ControllerAdvice;
 import org.springframework.web.bind.annotation.ExceptionHandler;
 import org.springframework.web.bind.annotation.ResponseStatus;
@@ -41,11 +43,19 @@ public interface AdviceTrait {
     default ThrowableProblem toProblem(final Throwable throwable) {
         final StatusType status = Optional.ofNullable(resolveResponseStatus(throwable))
                 .<StatusType>map(ResponseStatusAdapter::new)
+                .or(() -> Optional.ofNullable(resolveStatusFromErrorResponse(throwable)))
                 .orElse(Status.INTERNAL_SERVER_ERROR);
 
         return toProblem(throwable, status);
     }
 
+    default StatusType resolveStatusFromErrorResponse(final Throwable type) {
+        if (!(type instanceof ErrorResponse)) return null;
+
+        final HttpStatusCode code = ((ErrorResponse) type).getStatusCode();
+        return Status.valueOf(code.value());
+    }
+
     @API(status = MAINTAINED)
     default ResponseStatus resolveResponseStatus(final Throwable type) {
         @Nullable final ResponseStatus candidate = findMergedAnnotation(type.getClass(), ResponseStatus.class);

problem-spring-common/src/test/java/org/zalando/problem/spring/common/AdviceTraitTest.java

@@ -2,7 +2,10 @@
 
 import org.junit.jupiter.api.Test;
 import org.springframework.http.HttpStatus;
+import org.springframework.http.HttpStatusCode;
+import org.springframework.http.ProblemDetail;
 import org.springframework.http.ResponseEntity;
+import org.springframework.web.ErrorResponse;
 import org.springframework.web.bind.annotation.ResponseStatus;
 import org.zalando.problem.Problem;
 import org.zalando.problem.Status;
@@ -29,6 +32,24 @@ public TestException(String message) {
         }
     }
 
+    class SpringExpception extends Throwable implements ErrorResponse {
+        final HttpStatus status;
+
+        SpringExpception(HttpStatus status) {
+            this.status = status;
+        }
+
+        @Override
+        public HttpStatusCode getStatusCode() {
+            return status;
+        }
+
+        @Override
+        public ProblemDetail getBody() {
+            return ProblemDetail.forStatusAndDetail(status, status.getReasonPhrase());
+        }
+    }
+
     @ResponseStatus(value = HttpStatus.RESET_CONTENT, reason = "reason")
     class TestExceptionWithReason extends RuntimeException {
         public TestExceptionWithReason(String message) {
@@ -56,6 +77,15 @@ void buildsOnResponseStatusThrowable() {
         assertThat(result.getDetail(), is("Message"));
     }
 
+    @Test
+    void buildsOnErrorResponseThrowable() {
+        final Problem result = unit.toProblem(new SpringExpception(HttpStatus.NOT_FOUND));
+
+        assertThat(result.getStatus().getStatusCode(), is(404));
+        assertThat(result.getType().toString(), is("about:blank"));
+        assertThat(result.getTitle(), is("Not Found"));
+    }
+
     @Test
     void buildsOnResponseStatusWithReasonThrowable() {
         final Problem result = unit.toProblem(new TestExceptionWithReason("Message"));
@@ -181,4 +211,4 @@ void processDoesNothing() {
         assertThat(result.getStatusCode(), is(HttpStatus.OK));
         assertThat(result.getBody().getStatus(), is(Status.RESET_CONTENT));
     }
-}
+}