Polish client support for HTTP PATCH

Issue: SPR-7985

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

@@ -17,7 +17,6 @@
 package org.springframework.http.client;
 
 import java.io.IOException;
-import java.lang.reflect.Constructor;
 import java.net.URI;
 
 import org.apache.http.client.HttpClient;
@@ -25,6 +24,7 @@ import org.apache.http.client.methods.HttpDelete;
 import org.apache.http.client.methods.HttpGet;
 import org.apache.http.client.methods.HttpHead;
 import org.apache.http.client.methods.HttpOptions;
+import org.apache.http.client.methods.HttpPatch;
 import org.apache.http.client.methods.HttpPost;
 import org.apache.http.client.methods.HttpPut;
 import org.apache.http.client.methods.HttpTrace;
@@ -56,6 +56,9 @@ import org.springframework.util.ClassUtils;
  */
 public class HttpComponentsClientHttpRequestFactory implements ClientHttpRequestFactory, DisposableBean {
 
+	private static final boolean HTTP_PATCH_AVAILABLE = ClassUtils.isPresent(
+			"org.apache.http.client.methods.HttpPatch", HttpComponentsClientHttpRequestFactory.class.getClassLoader());
+
 	private static final int DEFAULT_MAX_TOTAL_CONNECTIONS = 100;
 
 	private static final int DEFAULT_MAX_CONNECTIONS_PER_ROUTE = 5;
@@ -164,19 +167,12 @@ public class HttpComponentsClientHttpRequestFactory implements ClientHttpRequest
 	}
 
 	private HttpUriRequest createHttpPatch(URI uri) {
-		String className = "org.apache.http.client.methods.HttpPatch";
-		ClassLoader classloader = this.getClass().getClassLoader();
-		if (!ClassUtils.isPresent(className, classloader)) {
+		if (!HTTP_PATCH_AVAILABLE) {
 			throw new IllegalArgumentException(
 					"HTTP method PATCH not available before Apache HttpComponents HttpClient 4.2");
 		}
-		try {
-			Class<?> clazz = classloader.loadClass(className);
-			Constructor<?> constructor = clazz.getConstructor(URI.class);
-			return (HttpUriRequest) constructor.newInstance(uri);
-		}
-		catch (Throwable ex) {
-			throw new IllegalStateException("Unable to instantiate " + className, ex);
+		else {
+			return new HttpPatch(uri);
 		}
 	}
 

spring-web/src/main/java/org/springframework/web/client/RestTemplate.java

@@ -69,6 +69,10 @@ import org.springframework.web.util.UriUtils;
  * <tr><td>any</td><td>{@link #exchange}</td></tr>
  * <tr><td></td><td>{@link #execute}</td></tr> </table>
  *
+ * <p>The {@code exchange} and {@code execute} methods are generalized versions of the more specific methods listed
+ * above them. They support additional, less frequently used combinations including support for requests using the
+ * HTTP PATCH method. However, note that the underlying HTTP library must also support the desired combination.</p>
+ *
  * <p>For each of these HTTP methods, there are three corresponding Java methods in the {@code RestTemplate}. Two
  * variant take a {@code String} URI as first argument (eg. {@link #getForObject(String, Class, Object[])}, {@link
  * #getForObject(String, Class, Map)}), and are capable of substituting any {@linkplain UriTemplate URI templates} in