Modify @RequestParam presence handling

extensions/spring-web/resteasy-reactive/runtime/src/main/java/io/quarkus/spring/web/resteasy/reactive/runtime/SpringRequestParamHandler.java

@@ -4,7 +4,9 @@
 import java.util.List;
 import java.util.Map;
 
-import org.jboss.resteasy.reactive.common.jaxrs.ResponseImpl;
+import jakarta.ws.rs.WebApplicationException;
+import jakarta.ws.rs.core.Response;
+
 import org.jboss.resteasy.reactive.common.model.ResourceClass;
 import org.jboss.resteasy.reactive.server.core.ResteasyReactiveRequestContext;
 import org.jboss.resteasy.reactive.server.model.HandlerChainCustomizer;
@@ -21,18 +23,19 @@ public class SpringRequestParamHandler implements HandlerChainCustomizer {
     @Override
     public List<ServerRestHandler> handlers(HandlerChainCustomizer.Phase phase, ResourceClass resourceClass,
             ServerResourceMethod resourceMethod) {
-        if (phase == Phase.AFTER_RESPONSE_CREATED) {
+        if (phase == Phase.RESOLVE_METHOD_PARAMETERS) {
             return Collections.singletonList(new ServerRestHandler() {
                 @Override
                 public void handle(ResteasyReactiveRequestContext requestContext) throws Exception {
                     Map<String, List<String>> parametersMap = requestContext.serverRequest().getQueryParamsMap();
                     if (parametersMap.isEmpty()) {
-                        ResponseImpl response = (ResponseImpl) requestContext.getResponse().get();
-                        response.setStatus(400);
+                        throw new WebApplicationException("Missing required param in method '" + resourceMethod.getName() + "'",
+                                Response.Status.BAD_REQUEST);
                     }
                 }
             });
         }
         return Collections.emptyList();
     }
+
 }

extensions/spring-web/resteasy-reactive/tests/src/test/java/io/quarkus/spring/web/requestparam/RequestParamController.java

@@ -5,13 +5,19 @@
 import java.util.Optional;
 import java.util.stream.Collectors;
 
+import jakarta.ws.rs.WebApplicationException;
+
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
 import org.springframework.util.MultiValueMap;
+import org.springframework.web.bind.annotation.ExceptionHandler;
 import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.PostMapping;
 import org.springframework.web.bind.annotation.RequestMapping;
 import org.springframework.web.bind.annotation.RequestParam;
 import org.springframework.web.bind.annotation.ResponseBody;
 import org.springframework.web.bind.annotation.RestController;
+import org.springframework.web.bind.annotation.RestControllerAdvice;
 
 @RestController
 @RequestMapping
@@ -69,4 +75,18 @@ public String updateFoos(@RequestParam MultiValueMap<String, String> allParams)
         return result;
     }
 
+    @GetMapping("/api/foos/paramRequired")
+    public String getFoosParamRequired(@RequestParam String id) {
+        throw new IllegalStateException("Unexpected state. Should have not been called");
+    }
+
+    @RestControllerAdvice
+    public static class RestExceptionHandler {
+
+        @ExceptionHandler(WebApplicationException.class)
+        public ResponseEntity<Object> handleException(Exception ex) {
+            return new ResponseEntity<>(ex.getMessage(), HttpStatus.BAD_REQUEST);
+        }
+    }
+
 }

extensions/spring-web/resteasy-reactive/tests/src/test/java/io/quarkus/spring/web/requestparam/RequestParamControllerTest.java

@@ -26,7 +26,7 @@ public void testSimpleMapping() throws Exception {
         // In Spring, method parameters annotated with @RequestParam are required by default.
         when().get("/api/foos")
                 .then()
-                .statusCode(400);
+                .statusCode(400).body(containsString("Missing required param in method"));
     }
 
     @Test
@@ -123,4 +123,12 @@ public void testMultiMap() throws Exception {
                 .statusCode(400);
     }
 
+    @Test
+    public void shouldFailWithBadRequestWhenMissingMandatoryParam() throws Exception {
+        // In Spring, method parameters annotated with @RequestParam are required by default.
+        when().get("/api/foos/paramRequired")
+                .then()
+                .statusCode(400).body(containsString("Missing required param in method"));
+    }
+
 }