Use HTTP methods in JdkClientHttpRequest when possible

Prior to this commit, we would use the
`java.net.http.HttpRequest.Builder#method(String, BodyPublisher)` to
create HTTP requests for the JDK HttpClient. This method requires a
non-null body publisher; providing an empty publisher writes a
"Content-Length: 0" header to all requests.

As of Java 19, this behavior changes for `HttpRequest.Builder#GET` and
similar methods, where the body publisher is considered as null and no
"Content-Length" header is written.

This commit aligns with this behavior and favors dedicated HTTP methods
whenever available.`

Closes gh-34971

spring-web/src/main/java/org/springframework/http/client/JdkClientHttpRequest.java

@@ -149,7 +149,16 @@ class JdkClientHttpRequest extends AbstractStreamingClientHttpRequest {
 			}
 		});
 
+		switch (this.method.name()) {
+			case "GET" :
+				builder.GET();
+				break;
+			case "DELETE" :
+				builder.DELETE();
+				break;
+			default :
 				builder.method(this.method.name(), bodyPublisher(headers, body));
+		}
 		return builder.build();
 	}
 

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

@@ -18,15 +18,19 @@ package org.springframework.http.client;
 
 import java.io.IOException;
 import java.net.URI;
+import java.nio.charset.StandardCharsets;
 
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.condition.EnabledForJreRange;
+import org.junit.jupiter.api.condition.JRE;
 
 import org.springframework.http.HttpMethod;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.HttpStatusCode;
 import org.springframework.lang.Nullable;
+import org.springframework.util.StreamUtils;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
@@ -34,6 +38,7 @@ import static org.assertj.core.api.Assertions.assertThat;
  * Tests for {@link JdkClientHttpRequestFactory}.
  *
  * @author Marten Deinum
+ * @author Brian Clozel
  */
 class JdkClientHttpRequestFactoryTests extends AbstractHttpRequestFactoryTests {
 
@@ -88,4 +93,22 @@ class JdkClientHttpRequestFactoryTests extends AbstractHttpRequestFactoryTests {
 		}
 	}
 
+
+	@Test // gh-34971
+	@EnabledForJreRange(min = JRE.JAVA_19) // behavior fixed in Java 19
+	void requestContentLengthHeader() throws Exception {
+		URI uri = URI.create(baseUrl + "/header/Content-Length");
+		assertNoContentLength(uri, HttpMethod.GET);
+		assertNoContentLength(uri, HttpMethod.DELETE);
+	}
+
+	protected void assertNoContentLength(URI uri, HttpMethod method) throws Exception {
+		ClientHttpRequest request = factory.createRequest(uri, method);
+		try (ClientHttpResponse response = request.execute()) {
+			assertThat(response.getStatusCode()).as("Invalid response status").isEqualTo(HttpStatus.OK);
+			assertThat(StreamUtils.copyToString(response.getBody(), StandardCharsets.ISO_8859_1))
+					.as("Invalid Content-Length request header").isEqualTo("Content-Length:null");
+		}
+	}
+
 }