Fix RouterFunction.andRoute()

Fixed RouterFunction.andRoute signature.

Issue: SPR-14904

spring-web-reactive/src/main/java/org/springframework/web/reactive/function/RouterFunction.java

@@ -78,12 +78,13 @@ public interface RouterFunction<T> {
 	 * {@link RouterFunctions#route(RequestPredicate, HandlerFunction)}.
 	 * @param predicate the predicate to test
 	 * @param handlerFunction the handler function to route to
+	 * @param <S> the handler function type
 	 * @return a composed function that first routes with this function and then the function
 	 * created from {@code predicate} and {@code handlerFunction} if this
 	 * function has no result
 	 */
-	default RouterFunction<?> andRoute(RequestPredicate predicate,
+	default <S> RouterFunction<?> andRoute(RequestPredicate predicate,
-			HandlerFunction<?> handlerFunction) {
+			HandlerFunction<S> handlerFunction) {
 		return and(RouterFunctions.route(predicate, handlerFunction));
 	}
 

spring-web-reactive/src/test/java/org/springframework/web/reactive/function/RouterFunctionTests.java

@@ -61,6 +61,23 @@ public class RouterFunctionTests {
 		assertEquals(handlerFunction, resultHandlerFunction.get());
 	}
 
+	@Test
+	public void andRoute() throws Exception {
+		RouterFunction<Integer> routerFunction1 = request -> Optional.empty();
+		RequestPredicate requestPredicate = request -> true;
+
+		RouterFunction<?> result = routerFunction1.andRoute(requestPredicate, this::handlerMethod);
+		assertNotNull(result);
+
+		MockServerRequest request = MockServerRequest.builder().build();
+		Optional<? extends HandlerFunction<?>> resultHandlerFunction = result.route(request);
+		assertTrue(resultHandlerFunction.isPresent());
+	}
+
+	private ServerResponse<String> handlerMethod(ServerRequest request) {
+		return ServerResponse.ok().body(fromObject("42"));
+	}
+
 	@Test
 	public void filter() throws Exception {
 		HandlerFunction<String> handlerFunction = request -> ServerResponse.ok().body(fromObject("42"));