Polish "Support default headers with RestTemplateBuilder"

Broaden the scope of customizer support so that instead of focusing
just on headers, we can now customize any outgoing `HttpClientRequest`.
Also update auto-configuration to automatically add any
`RestTemplateRequestCustomizer` beans to the builder.

See gh-17091

Author: philwebb

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/client/RestTemplateAutoConfiguration.java

@@ -16,7 +16,9 @@
 
 package org.springframework.boot.autoconfigure.web.client;
 
+import java.util.Collection;
 import java.util.List;
+import java.util.function.BiFunction;
 import java.util.stream.Collectors;
 
 import org.springframework.beans.factory.ObjectProvider;
@@ -32,6 +34,7 @@
 import org.springframework.boot.autoconfigure.web.client.RestTemplateAutoConfiguration.NotReactiveWebApplicationCondition;
 import org.springframework.boot.web.client.RestTemplateBuilder;
 import org.springframework.boot.web.client.RestTemplateCustomizer;
+import org.springframework.boot.web.client.RestTemplateRequestCustomizer;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Conditional;
 import org.springframework.context.annotation.Configuration;
@@ -53,15 +56,23 @@ public class RestTemplateAutoConfiguration {
 	@Bean
 	@ConditionalOnMissingBean
 	public RestTemplateBuilder restTemplateBuilder(ObjectProvider<HttpMessageConverters> messageConverters,
-			ObjectProvider<RestTemplateCustomizer> restTemplateCustomizers) {
+			ObjectProvider<RestTemplateCustomizer> restTemplateCustomizers,
+			ObjectProvider<RestTemplateRequestCustomizer<?>> restTemplateRequestCustomizers) {
 		RestTemplateBuilder builder = new RestTemplateBuilder();
 		HttpMessageConverters converters = messageConverters.getIfUnique();
 		if (converters != null) {
 			builder = builder.messageConverters(converters.getConverters());
 		}
-		List<RestTemplateCustomizer> customizers = restTemplateCustomizers.orderedStream().collect(Collectors.toList());
+		builder = addCustomizers(builder, restTemplateCustomizers, RestTemplateBuilder::customizers);
+		builder = addCustomizers(builder, restTemplateRequestCustomizers, RestTemplateBuilder::requestCustomizers);
+		return builder;
+	}
+
+	private <T> RestTemplateBuilder addCustomizers(RestTemplateBuilder builder, ObjectProvider<T> objectProvider,
+			BiFunction<RestTemplateBuilder, Collection<T>, RestTemplateBuilder> method) {
+		List<T> customizers = objectProvider.orderedStream().collect(Collectors.toList());
 		if (!customizers.isEmpty()) {
-			builder = builder.customizers(customizers);
+			return method.apply(builder, customizers);
 		}
 		return builder;
 	}

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/client/RestTemplateAutoConfigurationTests.java

@@ -16,6 +16,7 @@
 
 package org.springframework.boot.autoconfigure.web.client;
 
+import java.util.Collections;
 import java.util.List;
 
 import org.junit.jupiter.api.Test;
@@ -28,14 +29,21 @@
 import org.springframework.boot.test.context.runner.WebApplicationContextRunner;
 import org.springframework.boot.web.client.RestTemplateBuilder;
 import org.springframework.boot.web.client.RestTemplateCustomizer;
+import org.springframework.boot.web.client.RestTemplateRequestCustomizer;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.client.ClientHttpRequestFactory;
 import org.springframework.http.client.HttpComponentsClientHttpRequestFactory;
 import org.springframework.http.converter.HttpMessageConverter;
 import org.springframework.http.converter.StringHttpMessageConverter;
+import org.springframework.mock.http.client.MockClientHttpRequest;
+import org.springframework.mock.http.client.MockClientHttpResponse;
 import org.springframework.web.client.RestTemplate;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.BDDMockito.given;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.verify;
 
@@ -109,6 +117,20 @@ void restTemplateShouldApplyCustomizer() {
 				});
 	}
 
+	@Test
+	void restTemplateShouldApplyRequestCustomizer() {
+		this.contextRunner.withUserConfiguration(RestTemplateRequestCustomizerConfig.class).run((context) -> {
+			RestTemplateBuilder builder = context.getBean(RestTemplateBuilder.class);
+			ClientHttpRequestFactory requestFactory = mock(ClientHttpRequestFactory.class);
+			MockClientHttpRequest request = new MockClientHttpRequest();
+			request.setResponse(new MockClientHttpResponse(new byte[0], HttpStatus.OK));
+			given(requestFactory.createRequest(any(), any())).willReturn(request);
+			RestTemplate restTemplate = builder.requestFactory(() -> requestFactory).build();
+			restTemplate.getForEntity("http://localhost:8080/test", String.class);
+			assertThat(request.getHeaders()).containsEntry("spring", Collections.singletonList("boot"));
+		});
+	}
+
 	@Test
 	void builderShouldBeFreshForEachUse() {
 		this.contextRunner.withUserConfiguration(DirtyRestTemplateConfig.class)
@@ -189,6 +211,16 @@ public RestTemplateCustomizer restTemplateCustomizer() {
 
 	}
 
+	@Configuration(proxyBeanMethods = false)
+	static class RestTemplateRequestCustomizerConfig {
+
+		@Bean
+		public RestTemplateRequestCustomizer<?> restTemplateRequestCustomizer() {
+			return (request) -> request.getHeaders().add("spring", "boot");
+		}
+
+	}
+
 	static class CustomHttpMessageConverter extends StringHttpMessageConverter {
 
 	}

spring-boot-project/spring-boot-test/src/test/java/org/springframework/boot/test/web/client/TestRestTemplateTests.java

@@ -100,7 +100,7 @@ void useTheSameRequestFactoryClassWithBasicAuth() {
 		TestRestTemplate testRestTemplate = new TestRestTemplate(builder).withBasicAuth("test", "test");
 		RestTemplate restTemplate = testRestTemplate.getRestTemplate();
 		assertThat(restTemplate.getRequestFactory().getClass().getName())
-				.contains("HttpHeadersCustomizingClientHttpRequestFactory");
+				.contains("RestTemplateBuilderClientHttpRequestFactoryWrapper");
 		Object requestFactory = ReflectionTestUtils.getField(restTemplate.getRequestFactory(), "requestFactory");
 		assertThat(requestFactory).isEqualTo(customFactory).hasSameClassAs(customFactory);
 	}
@@ -208,7 +208,7 @@ void withBasicAuthAddsBasicAuthClientFactoryWhenNotAlreadyPresent() throws Excep
 		TestRestTemplate basicAuth = original.withBasicAuth("user", "password");
 		assertThat(getConverterClasses(original)).containsExactlyElementsOf(getConverterClasses(basicAuth));
 		assertThat(basicAuth.getRestTemplate().getRequestFactory().getClass().getName())
-				.contains("HttpHeadersCustomizingClientHttpRequestFactory");
+				.contains("RestTemplateBuilderClientHttpRequestFactoryWrapper");
 		assertThat(ReflectionTestUtils.getField(basicAuth.getRestTemplate().getRequestFactory(), "requestFactory"))
 				.isInstanceOf(CustomHttpComponentsClientHttpRequestFactory.class);
 		assertThat(basicAuth.getRestTemplate().getInterceptors()).isEmpty();
@@ -221,7 +221,7 @@ void withBasicAuthReplacesBasicAuthClientFactoryWhenAlreadyPresent() throws Exce
 		TestRestTemplate basicAuth = original.withBasicAuth("user", "password");
 		assertThat(getConverterClasses(basicAuth)).containsExactlyElementsOf(getConverterClasses(original));
 		assertThat(basicAuth.getRestTemplate().getRequestFactory().getClass().getName())
-				.contains("HttpHeadersCustomizingClientHttpRequestFactory");
+				.contains("RestTemplateBuilderClientHttpRequestFactoryWrapper");
 		assertThat(ReflectionTestUtils.getField(basicAuth.getRestTemplate().getRequestFactory(), "requestFactory"))
 				.isInstanceOf(CustomHttpComponentsClientHttpRequestFactory.class);
 		assertThat(basicAuth.getRestTemplate().getInterceptors()).isEmpty();

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/client/AbstractHttpHeadersDefaultingCustomizer.java

@@ -22,34 +22,31 @@
 import org.springframework.util.Assert;
 
 /**
- * {@link AbstractHttpHeadersDefaultingCustomizer} that applies basic authentication
- * header unless it was provided in the request.
+ * Basic authentication details to be applied to {@link HttpHeaders}.
  *
  * @author Dmytro Nosan
  * @author Ilya Lukyanovich
- * @see HttpHeadersCustomizingClientHttpRequestFactory
  */
-class BasicAuthenticationHeaderDefaultingCustomizer extends AbstractHttpHeadersDefaultingCustomizer {
+class BasicAuthentication {
 
 	private final String username;
 
 	private final String password;
 
 	private final Charset charset;
 
-	BasicAuthenticationHeaderDefaultingCustomizer(String username, String password, Charset charset) {
+	BasicAuthentication(String username, String password, Charset charset) {
 		Assert.notNull(username, "Username must not be null");
 		Assert.notNull(password, "Password must not be null");
 		this.username = username;
 		this.password = password;
 		this.charset = charset;
 	}
 
-	@Override
-	protected HttpHeaders createHeaders() {
-		HttpHeaders headers = new HttpHeaders();
-		headers.setBasicAuth(this.username, this.password, this.charset);
-		return headers;
+	public void applyTo(HttpHeaders headers) {
+		if (!headers.containsKey(HttpHeaders.AUTHORIZATION)) {
+			headers.setBasicAuth(this.username, this.password, this.charset);
+		}
 	}
 
 }