Add defensive warning for multiple Feign Client beans to prevent potential resource exhaustion

Signed-off-by: 98001yash <yashchauhan.gaya@gmail.com>

Author: yashdotdev13

spring-cloud-openfeign-core/src/main/java/org/springframework/cloud/openfeign/FeignClientFactoryBean.java

@@ -59,6 +59,38 @@
 import org.springframework.util.StringUtils;
 
 /**
+ * A {@link FactoryBean} responsible for creating Feign client proxies.
+ *
+ * <p><strong>Note:</strong> Custom {@link Client} beans provided in a Feign client
+ * context should be singleton-scoped. Defining a prototype-scoped {@code Client}
+ * may lead to multiple underlying HTTP connection pools being created, which
+ * can result in resource exhaustion.
+ *
+ * @author Spencer Gibb
+ * @author Venil Noronha
+ * @author Eko Kurniawan Khannedy
+ * @author Gregor Zurowski
+ * @author Matt King
+ * @author Olga Maciaszek-Sharma
+ * @author Ilia Ilinykh
+ * @author Marcin Grzejszczak
+ * @author Jonatan Ivanov
+ * @author Sam Kruglov
+ * @author Jasbir Singh
+ * @author Hyeonmin Park
+ * @author Felix Dittrich
+ * @author Dominique Villard
+ * @author Can Bezmen
+ */
+/**
+ * A {@link FactoryBean} responsible for creating Feign client proxies.
+ *
+ * <p>
+ * <strong>Note:</strong> Custom {@link Client} beans provided in a Feign client context
+ * should be singleton-scoped. Defining a prototype-scoped {@code Client} may lead to
+ * multiple underlying HTTP connection pools being created, which can result in resource
+ * exhaustion.
+ *
  * @author Spencer Gibb
  * @author Venil Noronha
  * @author Eko Kurniawan Khannedy
@@ -465,42 +497,64 @@ public Object getObject() {
 	<T> T getTarget() {
 		FeignClientFactory feignClientFactory = beanFactory != null ? beanFactory.getBean(FeignClientFactory.class)
 				: applicationContext.getBean(FeignClientFactory.class);
+
 		Feign.Builder builder = feign(feignClientFactory);
+
 		if (!StringUtils.hasText(url) && !isUrlAvailableInConfig(contextId)) {
 
 			if (LOG.isInfoEnabled()) {
 				LOG.info("For '" + name + "' URL not provided. Will try picking an instance via load-balancing.");
 			}
+
 			if (!name.startsWith("http://") && !name.startsWith("https://")) {
 				url = "http://" + name;
 			}
 			else {
 				url = name;
 			}
+
 			url += cleanPath();
 			return (T) loadBalance(builder, feignClientFactory, new HardCodedTarget<>(type, name, url));
 		}
+
 		if (StringUtils.hasText(url) && !url.startsWith("http://") && !url.startsWith("https://")) {
 			url = "http://" + url;
 		}
+
 		Client client = getOptional(feignClientFactory, Client.class);
+
 		if (client != null) {
+
+			try {
+				Map<String, Client> clients = feignClientFactory.getInstances(contextId, Client.class);
+
+				if (clients != null && clients.size() > 1) {
+					LOG.warn("Multiple Feign Client beans detected for contextId '" + contextId
+							+ "'. Custom Client beans should typically be singleton-scoped "
+							+ "to avoid multiple underlying connection pools.");
+				}
+			}
+			catch (Exception ex) {
+				if (LOG.isDebugEnabled()) {
+					LOG.debug("Unable to inspect Feign Client beans for contextId '" + contextId + "'", ex);
+				}
+			}
+
 			if (client instanceof FeignBlockingLoadBalancerClient) {
-				// not load balancing because we have a url,
-				// but Spring Cloud LoadBalancer is on the classpath, so unwrap
 				client = ((FeignBlockingLoadBalancerClient) client).getDelegate();
 			}
+
 			if (client instanceof RetryableFeignBlockingLoadBalancerClient) {
-				// not load balancing because we have a url,
-				// but Spring Cloud LoadBalancer is on the classpath, so unwrap
 				client = ((RetryableFeignBlockingLoadBalancerClient) client).getDelegate();
 			}
+
 			builder.client(client);
 		}
 
 		applyBuildCustomizers(feignClientFactory, builder);
 
 		Targeter targeter = get(feignClientFactory, Targeter.class);
+
 		return targeter.target(this, builder, feignClientFactory, resolveTarget(feignClientFactory, contextId, url));
 	}