add tests and documentation

Author: kistlers

docs/modules/ROOT/pages/spring-cloud-openfeign.adoc

@@ -144,7 +144,7 @@ When it comes to the Apache HttpClient 5-backed Feign clients, it's enough to en
 You can customize the HTTP client used by providing a bean of either `org.apache.hc.client5.http.impl.classic.CloseableHttpClient` when using Apache HC5.
 
 You can further customise http clients by setting values in the `spring.cloud.openfeign.httpclient.xxx` properties. The ones prefixed just with `httpclient` will work for all the clients, the ones prefixed with `httpclient.hc5` to Apache HttpClient 5, and the ones prefixed with `httpclient.http2` to Http2Client. You can find a full list of properties you can customise in the appendix.
-If you can not configure Apache HttpClient 5 by using properties, there is an `HttpClient5FeignConfiguration.HttpClientBuilderCustomizer` interface for programmatic configuration.
+If you can not configure Apache HttpClient 5 by using properties, there is an `HttpClient5FeignConfiguration.HttpClientBuilderCustomizer` interface for programmatic configuration. Similarly, to configure the `HttpClientConnectionManager`, you can use `HttpClient5FeignConfiguration.HttpClientConnectionManagerBuilderCustomizer`.
 
 TIP: Apache HTTP Components `5.4` have changed defaults in the HttpClient relating to HTTP/1.1 TLS upgrades. Most proxy servers handle upgrades without issue, however, you may encounter issues with Envoy or Istio. If you need to restore previous behaviour, you can use `HttpClient5FeignConfiguration.HttpClientBuilderCustomizer` to do it, as shown in the example below.
 

spring-cloud-openfeign-core/src/test/java/org/springframework/cloud/openfeign/FeignHttpClient5ConfigurationTests.java

@@ -21,6 +21,7 @@
 import org.apache.hc.client5.http.impl.classic.CloseableHttpClient;
 import org.apache.hc.client5.http.impl.classic.HttpClientBuilder;
 import org.apache.hc.client5.http.impl.io.PoolingHttpClientConnectionManager;
+import org.apache.hc.client5.http.impl.io.PoolingHttpClientConnectionManagerBuilder;
 import org.apache.hc.client5.http.io.HttpClientConnectionManager;
 import org.junit.jupiter.api.Test;
 import org.mockito.Mockito;
@@ -29,6 +30,7 @@
 import org.springframework.boot.WebApplicationType;
 import org.springframework.boot.builder.SpringApplicationBuilder;
 import org.springframework.cloud.openfeign.clientconfig.HttpClient5FeignConfiguration.HttpClientBuilderCustomizer;
+import org.springframework.cloud.openfeign.clientconfig.HttpClient5FeignConfiguration.HttpClientConnectionManagerBuilderCustomizer;
 import org.springframework.context.ConfigurableApplicationContext;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
@@ -99,14 +101,35 @@ void shouldInstantiateHttpClient5ByUsingHttpClientBuilderCustomizer() {
 		}
 	}
 
+	@Test
+	void shouldInstantiateHttpClientConnectionManager5ByUsingHttpClientConnectionManagerBuilderCustomizer() {
+		ConfigurableApplicationContext context = new SpringApplicationBuilder().web(WebApplicationType.NONE)
+			.sources(FeignAutoConfiguration.class, Config.class)
+			.run();
+
+		HttpClientConnectionManager httpClientConnectionManager = context.getBean(HttpClientConnectionManager.class);
+		assertThat(httpClientConnectionManager).isNotNull();
+		HttpClientConnectionManagerBuilderCustomizer customizer = context.getBean(HttpClientConnectionManagerBuilderCustomizer.class);
+		verify(customizer).customize(any(PoolingHttpClientConnectionManagerBuilder.class));
+
+		if (context != null) {
+			context.close();
+		}
+	}
+
 	@Configuration
 	static class Config {
 
 		@Bean
-		HttpClientBuilderCustomizer customizer() {
+		HttpClientBuilderCustomizer httpClientCustomizer() {
 			return Mockito.mock(HttpClientBuilderCustomizer.class);
 		}
 
+		@Bean
+		HttpClientConnectionManagerBuilderCustomizer httpClientConnectionManagerCustomizer() {
+			return Mockito.mock(HttpClientConnectionManagerBuilderCustomizer.class);
+		}
+
 	}
 
 }