Extract ClientHttpRequestFactory detection to its own class

See gh-12707

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

+/*
+ * Copyright 2012-2018 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.web.client;
+
+import java.util.Collections;
+import java.util.LinkedHashMap;
+import java.util.Map;
+import java.util.function.Supplier;
+
+import org.springframework.beans.BeanUtils;
+import org.springframework.http.client.ClientHttpRequestFactory;
+import org.springframework.http.client.SimpleClientHttpRequestFactory;
+import org.springframework.util.ClassUtils;
+
+/**
+ * A supplier for {@link ClientHttpRequestFactory} that detects the preferred candidate
+ * based on the available implementations on the classpath.
+ *
+ * @author Stephane Nicoll
+ * @since 2.1.0
+ */
+public class ClientHttpRequestFactorySupplier
+		implements Supplier<ClientHttpRequestFactory> {
+
+	private static final Map<String, String> REQUEST_FACTORY_CANDIDATES;
+
+	static {
+		Map<String, String> candidates = new LinkedHashMap<>();
+		candidates.put("org.apache.http.client.HttpClient",
+				"org.springframework.http.client.HttpComponentsClientHttpRequestFactory");
+		candidates.put("okhttp3.OkHttpClient",
+				"org.springframework.http.client.OkHttp3ClientHttpRequestFactory");
+		REQUEST_FACTORY_CANDIDATES = Collections.unmodifiableMap(candidates);
+	}
+
+	@Override
+	public ClientHttpRequestFactory get() {
+		for (Map.Entry<String, String> candidate : REQUEST_FACTORY_CANDIDATES
+				.entrySet()) {
+			ClassLoader classLoader = getClass().getClassLoader();
+			if (ClassUtils.isPresent(candidate.getKey(), classLoader)) {
+				Class<?> factoryClass = ClassUtils.resolveClassName(candidate.getValue(),
+						classLoader);
+				return (ClientHttpRequestFactory) BeanUtils
+						.instantiateClass(factoryClass);
+			}
+		}
+		return new SimpleClientHttpRequestFactory();
+	}
+
+}

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

@@ -23,9 +23,7 @@ import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
-import java.util.LinkedHashMap;
 import java.util.LinkedHashSet;
-import java.util.Map;
 import java.util.Set;
 import java.util.function.Supplier;
 
@@ -33,11 +31,9 @@ import org.springframework.beans.BeanUtils;
 import org.springframework.http.client.AbstractClientHttpRequestFactoryWrapper;
 import org.springframework.http.client.ClientHttpRequestFactory;
 import org.springframework.http.client.ClientHttpRequestInterceptor;
-import org.springframework.http.client.SimpleClientHttpRequestFactory;
 import org.springframework.http.client.support.BasicAuthorizationInterceptor;
 import org.springframework.http.converter.HttpMessageConverter;
 import org.springframework.util.Assert;
-import org.springframework.util.ClassUtils;
 import org.springframework.util.CollectionUtils;
 import org.springframework.util.ReflectionUtils;
 import org.springframework.web.client.ResponseErrorHandler;
@@ -64,17 +60,6 @@ import org.springframework.web.util.UriTemplateHandler;
  */
 public class RestTemplateBuilder {
 
-	private static final Map<String, String> REQUEST_FACTORY_CANDIDATES;
-
-	static {
-		Map<String, String> candidates = new LinkedHashMap<>();
-		candidates.put("org.apache.http.client.HttpClient",
-				"org.springframework.http.client.HttpComponentsClientHttpRequestFactory");
-		candidates.put("okhttp3.OkHttpClient",
-				"org.springframework.http.client.OkHttp3ClientHttpRequestFactory");
-		REQUEST_FACTORY_CANDIDATES = Collections.unmodifiableMap(candidates);
-	}
-
 	private final boolean detectRequestFactory;
 
 	private final String rootUri;
@@ -561,7 +546,7 @@ public class RestTemplateBuilder {
 			requestFactory = this.requestFactorySupplier.get();
 		}
 		else if (this.detectRequestFactory) {
-			requestFactory = detectRequestFactory();
+			requestFactory = new ClientHttpRequestFactorySupplier().get();
 		}
 		if (requestFactory != null) {
 			ClientHttpRequestFactory unwrappedRequestFactory = unwrapRequestFactoryIfNecessary(
@@ -590,20 +575,6 @@ public class RestTemplateBuilder {
 		return unwrappedRequestFactory;
 	}
 
-	private ClientHttpRequestFactory detectRequestFactory() {
-		for (Map.Entry<String, String> candidate : REQUEST_FACTORY_CANDIDATES
-				.entrySet()) {
-			ClassLoader classLoader = getClass().getClassLoader();
-			if (ClassUtils.isPresent(candidate.getKey(), classLoader)) {
-				Class<?> factoryClass = ClassUtils.resolveClassName(candidate.getValue(),
-						classLoader);
-				return (ClientHttpRequestFactory) BeanUtils
-						.instantiateClass(factoryClass);
-			}
-		}
-		return new SimpleClientHttpRequestFactory();
-	}
-
 	private <T> Set<T> append(Set<T> set, T addition) {
 		Set<T> result = new LinkedHashSet<>(set != null ? set : Collections.emptySet());
 		result.add(addition);