Make ReactorClientHttpConnector lifecycle-aware

With this commit, ReactorClientHttpConnector now implements
SmartLifecycle which optionally allows recreating the HttpClient
after ReactorResourceFactory has been updated.

Closes gh-31180

spring-web/src/test/java/org/springframework/http/client/reactive/ReactorClientHttpConnectorTests.java

@@ -0,0 +1,71 @@
+/*
+ * Copyright 2002-2023 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.http.client.reactive;
+
+import java.util.function.Function;
+
+import org.junit.jupiter.api.Test;
+import reactor.netty.http.client.HttpClient;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * @author Sebastien Deleuze
+ */
+public class ReactorClientHttpConnectorTests {
+
+	@Test
+	void restartWithDefaultConstructor() {
+		ReactorClientHttpConnector connector = new ReactorClientHttpConnector();
+		assertThat(connector.isRunning()).isTrue();
+		connector.start();
+		assertThat(connector.isRunning()).isTrue();
+		connector.stop();
+		assertThat(connector.isRunning()).isFalse();
+		connector.start();
+		assertThat(connector.isRunning()).isTrue();
+	}
+
+	@Test
+	void restartWithExternalResourceFactory() {
+		ReactorResourceFactory resourceFactory = new ReactorResourceFactory();
+		resourceFactory.afterPropertiesSet();
+		Function<HttpClient, HttpClient> mapper = Function.identity();
+		ReactorClientHttpConnector connector = new ReactorClientHttpConnector(resourceFactory, mapper);
+		assertThat(connector.isRunning()).isTrue();
+		connector.start();
+		assertThat(connector.isRunning()).isTrue();
+		connector.stop();
+		assertThat(connector.isRunning()).isFalse();
+		connector.start();
+		assertThat(connector.isRunning()).isTrue();
+	}
+
+	@Test
+	void restartWithHttpClient() {
+		HttpClient httpClient = HttpClient.create();
+		ReactorClientHttpConnector connector = new ReactorClientHttpConnector(httpClient);
+		assertThat(connector.isRunning()).isTrue();
+		connector.start();
+		assertThat(connector.isRunning()).isTrue();
+		connector.stop();
+		assertThat(connector.isRunning()).isFalse();
+		connector.start();
+		assertThat(connector.isRunning()).isTrue();
+	}
+
+}