Auto-configure WebClient.Builder

This commit adds a new customizer interface for applying
configuration changes to `WebClient.Builder` beans:
`WebClientCustomizer`.

The new WebClient auto-configuration will make available, as a
prototype scoped bean, `WebClient.Builder` instances.
Once injected, developers can use those to create `WebClient`
instances to be used in their application.

`WebClientCustomizer` beans are sorted according to their
`Order` and then applied to the builder instances.

Closes gh-9522

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/reactive/WebFluxAutoConfigurationTests.java

@@ -105,9 +105,9 @@ public class WebFluxAutoConfigurationTests {
 				.getBean(RequestMappingHandlerAdapter.class);
 		assertThat((List<HandlerMethodArgumentResolver>) ReflectionTestUtils
 				.getField(adapter.getArgumentResolverConfigurer(), "customResolvers"))
-						.contains(
-								this.context.getBean("firstResolver",
-										HandlerMethodArgumentResolver.class),
+				.contains(
+						this.context.getBean("firstResolver",
+								HandlerMethodArgumentResolver.class),
 						this.context.getBean("secondResolver",
 								HandlerMethodArgumentResolver.class));
 	}

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/reactive/function/client/WebClientAutoConfigurationTests.java

@@ -0,0 +1,131 @@
+/*
+ * Copyright 2012-2017 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
+ *
+ *      http://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.boot.autoconfigure.web.reactive.function.client;
+
+import java.net.URI;
+
+import org.junit.After;
+import org.junit.Test;
+import reactor.core.publisher.Mono;
+
+import org.springframework.boot.web.reactive.function.client.WebClientCustomizer;
+import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.http.HttpMethod;
+import org.springframework.http.client.reactive.ClientHttpConnector;
+import org.springframework.web.reactive.function.client.WebClient;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.eq;
+import static org.mockito.BDDMockito.given;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+
+/**
+ * Tests for {@link WebClientAutoConfiguration}
+ *
+ * @author Brian Clozel
+ */
+public class WebClientAutoConfigurationTests {
+
+	private AnnotationConfigApplicationContext context;
+
+	@After
+	public void close() {
+		if (this.context != null) {
+			this.context.close();
+		}
+	}
+
+	@Test
+	public void webClientShouldApplyCustomizers() throws Exception {
+		load(WebClientCustomizerConfig.class);
+		WebClient.Builder builder = this.context.getBean(WebClient.Builder.class);
+		WebClientCustomizer customizer = this.context.getBean(WebClientCustomizer.class);
+		builder.build();
+		verify(customizer).customize(any(WebClient.Builder.class));
+	}
+
+	@Test
+	public void shouldGetPrototypeScopedBean() throws Exception {
+		load(WebClientCustomizerConfig.class);
+
+		ClientHttpConnector firstConnector = mock(ClientHttpConnector.class);
+		given(firstConnector.connect(any(), any(), any())).willReturn(Mono.empty());
+		WebClient.Builder firstBuilder = this.context.getBean(WebClient.Builder.class);
+		firstBuilder.clientConnector(firstConnector).baseUrl("http://first.example.org");
+
+		ClientHttpConnector secondConnector = mock(ClientHttpConnector.class);
+		given(secondConnector.connect(any(), any(), any())).willReturn(Mono.empty());
+		WebClient.Builder secondBuilder = this.context.getBean(WebClient.Builder.class);
+		secondBuilder.clientConnector(secondConnector).baseUrl("http://second.example.org");
+
+		assertThat(firstBuilder).isNotEqualTo(secondBuilder);
+
+		firstBuilder.build().get().uri("/foo").exchange().block();
+		secondBuilder.build().get().uri("/foo").exchange().block();
+
+		verify(firstConnector).connect(eq(HttpMethod.GET), eq(URI.create("http://first.example.org/foo")), any());
+		verify(secondConnector).connect(eq(HttpMethod.GET), eq(URI.create("http://second.example.org/foo")), any());
+		WebClientCustomizer customizer = this.context.getBean(WebClientCustomizer.class);
+		verify(customizer, times(1)).customize(any(WebClient.Builder.class));
+	}
+
+	@Test
+	public void shouldNotCreateClientBuilderIfAlreadyPresent() throws Exception {
+		load(WebClientCustomizerConfig.class, CustomWebClientBuilderConfig.class);
+		WebClient.Builder builder = this.context.getBean(WebClient.Builder.class);
+		assertThat(builder).isInstanceOf(MyWebClientBuilder.class);
+	}
+
+
+	private void load(Class<?>... config) {
+		AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
+		ctx.register(config);
+		ctx.register(WebClientAutoConfiguration.class);
+		ctx.refresh();
+		this.context = ctx;
+	}
+
+	@Configuration
+	static class WebClientCustomizerConfig {
+
+		@Bean
+		public WebClientCustomizer webClientCustomizer() {
+			return mock(WebClientCustomizer.class);
+		}
+
+	}
+
+	@Configuration
+	static class CustomWebClientBuilderConfig {
+
+		@Bean
+		public MyWebClientBuilder myWebClientBuilder() {
+			return mock(MyWebClientBuilder.class);
+		}
+
+	}
+
+	interface MyWebClientBuilder extends WebClient.Builder {
+
+	}
+
+}