Supports compiling and testing for java 16.

Moves kotlin compile to profile that is only activated on a jdk less than 16. This should change once kotlin supports java 16.

Deals with samples that use kotlin moving import to a selector only if the class exists and disabling a new test that tests the kotlin route.

Fixes gh-2186

spring-cloud-gateway-sample/src/main/java/org/springframework/cloud/gateway/sample/AdditionalRoutesImportSelector.java

@@ -0,0 +1,33 @@
+/*
+ * Copyright 2013-2021 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
+ *
+ *      https://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.cloud.gateway.sample;
+
+import org.springframework.context.annotation.DeferredImportSelector;
+import org.springframework.core.type.AnnotationMetadata;
+import org.springframework.util.ClassUtils;
+
+class AdditionalRoutesImportSelector implements DeferredImportSelector {
+
+	@Override
+	public String[] selectImports(AnnotationMetadata importingClassMetadata) {
+		if (ClassUtils.isPresent("org.springframework.cloud.gateway.sample.AdditionalRoutes", null)) {
+			return new String[] { "org.springframework.cloud.gateway.sample.AdditionalRoutes" };
+		}
+		return new String[0];
+	}
+
+}

spring-cloud-gateway-sample/src/main/java/org/springframework/cloud/gateway/sample/GatewaySampleApplication.java

@@ -41,7 +41,7 @@ import org.springframework.web.reactive.function.server.ServerResponse;
  */
 @SpringBootConfiguration
 @EnableAutoConfiguration
-@Import(AdditionalRoutes.class)
+@Import(AdditionalRoutesImportSelector.class)
 public class GatewaySampleApplication {
 
 	public static final String HELLO_FROM_FAKE_ACTUATOR_METRICS_GATEWAY_REQUESTS = "hello from fake /actuator/metrics/gateway.requests";

spring-cloud-gateway-sample/src/main/kotlin/org/springframework/cloud/gateway/sample/AdditionalRoutes.kt

@@ -32,7 +32,7 @@ open class AdditionalRoutes {
     @Bean
     open fun additionalRouteLocator(builder: RouteLocatorBuilder) = builder.routes {
         route(id = "test-kotlin") {
-            host("kotlin.abc.org") and path("/image/png")
+            host("kotlin.abc.org") and path("/anything/kotlinroute")
             filters {
                 prefixPath("/httpbin")
                 addResponseHeader("X-TestHeader", "foobar")

spring-cloud-gateway-sample/src/test/java/org/springframework/cloud/gateway/sample/GatewaySampleApplicationTests.java

@@ -22,11 +22,12 @@ import java.util.Map;
 
 import com.fasterxml.jackson.databind.JsonNode;
 import com.fasterxml.jackson.databind.ObjectMapper;
-import org.junit.AfterClass;
-import org.junit.Before;
-import org.junit.BeforeClass;
-import org.junit.Test;
-import org.junit.runner.RunWith;
+import org.junit.jupiter.api.AfterAll;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.condition.DisabledForJreRange;
+import org.junit.jupiter.api.condition.JRE;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
@@ -42,7 +43,6 @@ import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.Import;
 import org.springframework.core.env.Environment;
-import org.springframework.test.context.junit4.SpringRunner;
 import org.springframework.test.web.reactive.server.WebTestClient;
 import org.springframework.util.SocketUtils;
 
@@ -52,7 +52,6 @@ import static org.springframework.boot.test.context.SpringBootTest.WebEnvironmen
 /**
  * @author Spencer Gibb
  */
-@RunWith(SpringRunner.class)
 @SpringBootTest(classes = { GatewaySampleApplicationTests.TestConfig.class }, webEnvironment = RANDOM_PORT,
 		properties = "management.server.port=${test.port}")
 public class GatewaySampleApplicationTests {
@@ -69,19 +68,19 @@ public class GatewaySampleApplicationTests {
 
 	protected String baseUri;
 
-	@BeforeClass
+	@BeforeAll
 	public static void beforeClass() {
 		managementPort = SocketUtils.findAvailableTcpPort();
 
 		System.setProperty("test.port", String.valueOf(managementPort));
 	}
 
-	@AfterClass
+	@AfterAll
 	public static void afterClass() {
 		System.clearProperty("test.port");
 	}
 
-	@Before
+	@BeforeEach
 	public void setup() {
 		baseUri = "http://localhost:" + port;
 		this.webClient = WebTestClient.bindToServer().responseTimeout(Duration.ofSeconds(10)).baseUrl(baseUri).build();
@@ -157,7 +156,13 @@ public class GatewaySampleApplicationTests {
 	public void complexPredicate() {
 		webClient.get().uri("/anything/png").header("Host", "www.abc.org").exchange().expectHeader()
 				.valueEquals("X-TestHeader", "foobar").expectStatus().isOk();
+	}
 
+	@Test
+	@DisabledForJreRange(min = JRE.JAVA_16)
+	public void routeFromKotlin() {
+		webClient.get().uri("/anything/kotlinroute").header("Host", "kotlin.abc.org").exchange().expectHeader()
+				.valueEquals("X-TestHeader", "foobar").expectStatus().isOk();
 	}
 
 	@Test