Add buffering predicate to RestTemplate

See gh-33785

Author: rstoyanchev

Diff for: spring-web/src/main/java/org/springframework/http/client/support/HttpAccessor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * Copyright 2002-2025 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.
@@ -20,12 +20,15 @@
 import java.net.URI;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.function.BiPredicate;
 
 import org.apache.commons.logging.Log;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.core.annotation.AnnotationAwareOrderComparator;
 import org.springframework.http.HttpLogging;
 import org.springframework.http.HttpMethod;
+import org.springframework.http.client.BufferingClientHttpRequestFactory;
 import org.springframework.http.client.ClientHttpRequest;
 import org.springframework.http.client.ClientHttpRequestFactory;
 import org.springframework.http.client.ClientHttpRequestInitializer;
@@ -57,6 +60,8 @@ public abstract class HttpAccessor {
 
 	private final List<ClientHttpRequestInitializer> clientHttpRequestInitializers = new ArrayList<>();
 
+	private @Nullable BiPredicate<URI, HttpMethod> bufferingPredicate;
+
 
 	/**
 	 * Set the request factory that this accessor uses for obtaining client request handles.
@@ -78,10 +83,11 @@ public void setRequestFactory(ClientHttpRequestFactory requestFactory) {
 	 * Return the request factory that this accessor uses for obtaining client request handles.
 	 */
 	public ClientHttpRequestFactory getRequestFactory() {
-		return this.requestFactory;
+		return (this.bufferingPredicate != null ?
+				new BufferingClientHttpRequestFactory(this.requestFactory, this.bufferingPredicate) :
+				this.requestFactory);
 	}
 
-
 	/**
 	 * Set the request initializers that this accessor should use.
 	 * <p>The initializers will get immediately sorted according to their
@@ -111,6 +117,25 @@ public List<ClientHttpRequestInitializer> getClientHttpRequestInitializers() {
 		return this.clientHttpRequestInitializers;
 	}
 
+	/**
+	 * Enable buffering of request and response, aggregating all content before
+	 * it is sent, and making it possible to read the response body repeatedly.
+	 * @param predicate to determine whether to buffer for the given request
+	 * @since 7.0
+	 */
+	public void setBufferingPredicate(@Nullable BiPredicate<URI, HttpMethod> predicate) {
+		this.bufferingPredicate = predicate;
+	}
+
+	/**
+	 * Return the {@link #setBufferingPredicate(BiPredicate) configured} predicate
+	 * to determine whether to buffer request and response content.
+	 * @since 7.0
+	 */
+	public @Nullable BiPredicate<URI, HttpMethod> getBufferingPredicate() {
+		return this.bufferingPredicate;
+	}
+
 	/**
 	 * Create a new {@link ClientHttpRequest} via this template's {@link ClientHttpRequestFactory}.
 	 * @param url the URL to connect to

Diff for: spring-web/src/main/java/org/springframework/http/client/support/InterceptingHttpAccessor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2025 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.
@@ -99,7 +99,8 @@ public ClientHttpRequestFactory getRequestFactory() {
 		if (!CollectionUtils.isEmpty(interceptors)) {
 			ClientHttpRequestFactory factory = this.interceptingRequestFactory;
 			if (factory == null) {
-				factory = new InterceptingClientHttpRequestFactory(super.getRequestFactory(), interceptors);
+				factory = new InterceptingClientHttpRequestFactory(
+						super.getRequestFactory(), interceptors, getBufferingPredicate());
 				this.interceptingRequestFactory = factory;
 			}
 			return factory;

Diff for: spring-web/src/main/java/org/springframework/web/client/DefaultRestClientBuilder.java

@@ -185,6 +185,7 @@ public DefaultRestClientBuilder(RestTemplate restTemplate) {
 		if (!CollectionUtils.isEmpty(restTemplate.getInterceptors())) {
 			this.interceptors = new ArrayList<>(restTemplate.getInterceptors());
 		}
+		this.bufferingPredicate = restTemplate.getBufferingPredicate();
 		if (!CollectionUtils.isEmpty(restTemplate.getClientHttpRequestInitializers())) {
 			this.initializers = new ArrayList<>(restTemplate.getClientHttpRequestInitializers());
 		}

Diff for: spring-web/src/test/java/org/springframework/web/client/RestTemplateTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * Copyright 2002-2025 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.
@@ -52,10 +52,13 @@
 import org.springframework.http.converter.GenericHttpMessageConverter;
 import org.springframework.http.converter.HttpMessageConverter;
 import org.springframework.http.converter.SmartHttpMessageConverter;
+import org.springframework.http.converter.StringHttpMessageConverter;
 import org.springframework.http.converter.json.KotlinSerializationJsonHttpMessageConverter;
 import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
+import org.springframework.util.FileCopyUtils;
 import org.springframework.web.util.DefaultUriBuilderFactory;
 
+import static java.nio.charset.StandardCharsets.UTF_8;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
 import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
@@ -765,6 +768,46 @@ void requestInterceptorCanAddExistingHeaderValueWithBody() throws Exception {
 		verify(response).close();
 	}
 
+	@Test
+	void requestInterceptorWithBuffering() throws Exception {
+		try (MockWebServer server = new MockWebServer()) {
+			server.enqueue(new MockResponse().setResponseCode(200).setBody("Hello Spring!"));
+			server.start();
+			template.setRequestFactory(new SimpleClientHttpRequestFactory());
+			template.setInterceptors(List.of((request, body, execution) -> {
+				ClientHttpResponse response = execution.execute(request, body);
+				byte[] result = FileCopyUtils.copyToByteArray(response.getBody());
+				assertThat(result).isEqualTo("Hello Spring!".getBytes(UTF_8));
+				return response;
+			}));
+			template.setBufferingPredicate((uri, httpMethod) -> true);
+			template.setMessageConverters(List.of(new StringHttpMessageConverter()));
+			String result = template.getForObject(server.url("/").uri(), String.class);
+			assertThat(server.getRequestCount()).isEqualTo(1);
+			assertThat(result).isEqualTo("Hello Spring!");
+		}
+	}
+
+	@Test
+	void buffering() throws Exception {
+		try (MockWebServer server = new MockWebServer()) {
+			server.enqueue(new MockResponse().setResponseCode(200).setBody("Hello Spring!"));
+			server.start();
+			template.setRequestFactory(new SimpleClientHttpRequestFactory());
+			template.setBufferingPredicate((uri, httpMethod) -> true);
+			template.setMessageConverters(List.of(new StringHttpMessageConverter()));
+			String result = template.execute(server.url("/").uri(), HttpMethod.GET, req -> {}, response -> {
+				byte[] bytes = FileCopyUtils.copyToByteArray(response.getBody());
+				assertThat(bytes).isEqualTo("Hello Spring!".getBytes(UTF_8));
+				bytes = FileCopyUtils.copyToByteArray(response.getBody());
+				assertThat(bytes).isEqualTo("Hello Spring!".getBytes(UTF_8));
+				return new String(bytes, UTF_8);
+			});
+			assertThat(server.getRequestCount()).isEqualTo(1);
+			assertThat(result).isEqualTo("Hello Spring!");
+		}
+	}
+
 	@Test
 	void clientHttpRequestInitializerAndRequestInterceptorAreBothApplied() throws Exception {
 		ClientHttpRequestInitializer initializer = request ->