GH-577 Ensure listeners are notified after dispatch

aws-serverless-java-container-core/src/main/java/com/amazonaws/serverless/proxy/internal/servlet/AwsAsyncContext.java

@@ -74,8 +74,8 @@ public void dispatch() {
                 throw new IllegalStateException("Dispatching already started");
             }
             dispatched.set(true);
-            notifyListeners(NotificationType.START_ASYNC, null);
             handler.doFilter(req, res, ((AwsServletContext)req.getServletContext()).getServletForPath(req.getRequestURI()));
+            notifyListeners(NotificationType.START_ASYNC, null);
         } catch (ServletException | IOException e) {
             notifyListeners(NotificationType.ERROR, e);
         }

aws-serverless-java-container-core/src/main/java/com/amazonaws/serverless/proxy/internal/servlet/AwsHttpServletResponse.java

@@ -322,6 +322,10 @@ public void write(int b) throws IOException {
                 }
             }
 
+            @Override
+            public void flush() throws IOException {
+                flushBuffer();
+            }
 
             @Override
             public void close()

aws-serverless-java-container-springboot3/src/test/java/com/amazonaws/serverless/proxy/spring/ServletAppTest.java

@@ -38,6 +38,17 @@ public void initServletAppTest(String reqType) {
         handler = new LambdaHandler(type);
     }
 
+    @MethodSource("data")
+    @ParameterizedTest
+    void asyncRequest(String reqType) {
+        initServletAppTest(reqType);
+        AwsProxyRequestBuilder req = new AwsProxyRequestBuilder("/async", "POST")
+                .json()
+                .body("{\"name\":\"bob\"}");
+        AwsProxyResponse resp = handler.handleRequest(req, lambdaContext);
+        assertEquals("{\"name\":\"BOB\"}", resp.getBody());
+    }
+
     @MethodSource("data")
     @ParameterizedTest
     void helloRequest_respondsWithSingleMessage(String reqType) {

aws-serverless-java-container-springboot3/src/test/java/com/amazonaws/serverless/proxy/spring/servletapp/MessageController.java

@@ -5,9 +5,13 @@
 import org.springframework.http.ResponseEntity;
 import org.springframework.validation.Errors;
 import org.springframework.web.bind.annotation.*;
+import org.springframework.web.context.request.async.DeferredResult;
 import org.springframework.web.server.ResponseStatusException;
 
 import jakarta.validation.Valid;
+import reactor.core.publisher.Mono;
+
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
 
@@ -18,6 +22,22 @@ public class MessageController {
     public static final String UTF8_RESPONSE = "öüäß фрыцшщ";
     public static final String EX_MESSAGE = "404 exception message";
 
+
+    @RequestMapping(path="/hi", method=RequestMethod.GET, produces = {"text/plain"})
+    public Mono<String> hi() {
+        return Mono.just(HELLO_MESSAGE);
+    }
+
+    @SuppressWarnings({ "unchecked", "rawtypes" })
+	@RequestMapping(path = "/async", method = RequestMethod.POST)
+	@ResponseBody
+	public DeferredResult<Map<String, String>> asyncResult(@RequestBody Map<String, String> value) {
+		DeferredResult result = new DeferredResult<>();
+		result.setResult(Collections.singletonMap("name", value.get("name").toUpperCase()));
+		return result;
+	}
+
+
     @RequestMapping(path="/hello", method=RequestMethod.GET, produces = {"text/plain"})
     public String hello() {
         return HELLO_MESSAGE;