Merge pull request spring-projects#412 from OlgaMaciaszek/spring-projectsgh-304-add-discovery-clients-order-support

Gh 304 add discovery clients order support

Author: OlgaMaciaszek

docs/src/main/asciidoc/spring-cloud-commons.adoc

@@ -254,6 +254,17 @@ To disable it, set `spring.cloud.discovery.client.health-indicator.enabled=false
 To disable the description field of the `DiscoveryClientHealthIndicator`, set `spring.cloud.discovery.client.health-indicator.include-description=false`.
 Otherwise, it can bubble up as the `description` of the rolled up `HealthIndicator`.
 
+==== Ordering `DiscoveryClient` instances
+`DiscoveryClient` interface extends `Ordered`. This is useful when using multiple discovery
+ clients, as it allows you to define the order of the returned discovery clients, similar to
+how you can order the beans loaded by a Spring application. By default, the order of any `DiscoveryClient` is set to
+`0`. If you want to set a different order for your custom `DiscoveryClient` implementations, you just need to override
+the `getOrder()` method so that it returns the value that is suitable for your setup. Apart from this, you can use
+properties to set the order of the `DiscoveryClient`
+implementations provided by Spring Cloud, among others  `ConsulDiscoveryClient`, `EurekaDiscoveryClient` and
+`ZookeeperDiscoveryClient`. In order to do it, you just need to set the
+`spring.cloud.{clientIdentifier}.discovery.order` (or `eureka.client.order` for Eureka) property to the desired value.
+
 === ServiceRegistry
 
 Commons now provides a `ServiceRegistry` interface that provides methods such as `register(Registration)` and `deregister(Registration)`, which let you provide custom registered services.

spring-cloud-commons/src/main/java/org/springframework/cloud/client/discovery/DiscoveryClient.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2013-2015 the original author or authors.
+ * Copyright 2013-2018 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.
@@ -19,22 +19,29 @@
 import java.util.List;
 
 import org.springframework.cloud.client.ServiceInstance;
+import org.springframework.core.Ordered;
 
 /**
  * Represents read operations commonly available to discovery services such as Netflix
  * Eureka or consul.io.
+ *
  * @author Spencer Gibb
+ * @author Olga Maciaszek-Sharma
  */
-public interface DiscoveryClient {
+public interface DiscoveryClient extends Ordered {
+
+	int DEFAULT_ORDER = 0;
 
 	/**
 	 * A human-readable description of the implementation, used in HealthIndicator.
+	 *
 	 * @return The description.
 	 */
 	String description();
 
 	/**
 	 * Gets all ServiceInstances associated with a particular serviceId.
+	 *
 	 * @param serviceId The serviceId to query.
 	 * @return A List of ServiceInstance.
 	 */
@@ -45,4 +52,13 @@ public interface DiscoveryClient {
 	 */
 	List<String> getServices();
 
+	/**
+	 * Default implementation for getting order of discovery clients.
+	 *
+	 * @return order
+	 */
+	@Override
+	default int getOrder() {
+		return DEFAULT_ORDER;
+	}
 }

spring-cloud-commons/src/main/java/org/springframework/cloud/client/discovery/composite/CompositeDiscoveryClient.java

@@ -1,3 +1,19 @@
+/*
+ * Copyright 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.cloud.client.discovery.composite;
 
 import java.util.ArrayList;
@@ -7,18 +23,21 @@
 
 import org.springframework.cloud.client.ServiceInstance;
 import org.springframework.cloud.client.discovery.DiscoveryClient;
+import org.springframework.core.annotation.AnnotationAwareOrderComparator;
 
 /**
  * A {@link DiscoveryClient} that is composed of other discovery clients and delegates
  * calls to each of them in order.
  * 
  * @author Biju Kunjummen
+ * @author Olga Maciaszek-Sharma
  */
 public class CompositeDiscoveryClient implements DiscoveryClient {
 
 	private final List<DiscoveryClient> discoveryClients;
 
 	public CompositeDiscoveryClient(List<DiscoveryClient> discoveryClients) {
+		AnnotationAwareOrderComparator.sort(discoveryClients);
 		this.discoveryClients = discoveryClients;
 	}
 

spring-cloud-commons/src/main/java/org/springframework/cloud/client/discovery/simple/SimpleDiscoveryClient.java

@@ -1,3 +1,19 @@
+/*
+ * Copyright 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.cloud.client.discovery.simple;
 
 import java.util.ArrayList;
@@ -12,6 +28,7 @@
  * properties file as a source of service instances.
  *
  * @author Biju Kunjummen
+ * @author Olga Maciaszek-Sharma
  */
 public class SimpleDiscoveryClient implements DiscoveryClient {
 
@@ -42,4 +59,9 @@ public List<ServiceInstance> getInstances(String serviceId) {
 	public List<String> getServices() {
 		return new ArrayList<>(this.simpleDiscoveryProperties.getInstances().keySet());
 	}
+
+	@Override
+	public int getOrder() {
+		return this.simpleDiscoveryProperties.getOrder();
+	}
 }

spring-cloud-commons/src/main/java/org/springframework/cloud/client/discovery/simple/SimpleDiscoveryProperties.java

@@ -1,3 +1,19 @@
+/*
+ * Copyright 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.cloud.client.discovery.simple;
 
 import java.net.URI;
@@ -10,13 +26,18 @@
 
 import org.springframework.boot.context.properties.ConfigurationProperties;
 import org.springframework.cloud.client.ServiceInstance;
+import org.springframework.cloud.client.discovery.DiscoveryClient;
 
 /**
  * Properties to hold the details of a
  * {@link org.springframework.cloud.client.discovery.DiscoveryClient} service instances
  * for a given service.
+ * It also holds the user-configurable order that will be used to establish the
+ * precedence of this client in the list of clients
+ * used by {@link org.springframework.cloud.client.discovery.composite.CompositeDiscoveryClient}.
  *
  * @author Biju Kunjummen
+ * @author Olga Maciaszek-Sharma
  */
 
 @ConfigurationProperties(prefix = "spring.cloud.discovery.client.simple")
@@ -30,6 +51,8 @@ public class SimpleDiscoveryProperties {
 	 */
 	private SimpleServiceInstance local = new SimpleServiceInstance();
 
+	private int order = DiscoveryClient.DEFAULT_ORDER;
+
 	public Map<String, List<SimpleServiceInstance>> getInstances() {
 		return this.instances;
 	}
@@ -42,6 +65,14 @@ public SimpleServiceInstance getLocal() {
 		return this.local;
 	}
 
+	public int getOrder() {
+		return this.order;
+	}
+
+	public void setOrder(int order) {
+		this.order = order;
+	}
+
 	@PostConstruct
 	public void init() {
 		for (String key : this.instances.keySet()) {

spring-cloud-commons/src/test/java/org/springframework/cloud/client/discovery/composite/CompositeDiscoveryClientOrderTest.java

@@ -0,0 +1,76 @@
+/*
+ * Copyright 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.cloud.client.discovery.composite;
+
+import java.util.List;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.cloud.client.ServiceInstance;
+import org.springframework.cloud.client.discovery.DiscoveryClient;
+import org.springframework.test.context.junit4.SpringRunner;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.springframework.cloud.client.discovery.composite.CompositeDiscoveryClientTestsConfig.CUSTOM_DISCOVERY_CLIENT;
+import static org.springframework.cloud.client.discovery.composite.CompositeDiscoveryClientTestsConfig.CUSTOM_SERVICE_ID;
+import static org.springframework.cloud.client.discovery.composite.CompositeDiscoveryClientTestsConfig.DEFAULT_ORDER_DISCOVERY_CLIENT;
+import static org.springframework.cloud.client.discovery.composite.CompositeDiscoveryClientTestsConfig.FOURTH_DISCOVERY_CLIENT;
+
+/**
+ * Tests for the support of ordered {@link DiscoveryClient} instances in {@link CompositeDiscoveryClient}
+ *
+ * @author Olga Maciaszek-Sharma
+ */
+@RunWith(SpringRunner.class)
+@SpringBootTest(properties = "spring.cloud.discovery.client.simple.order:2", classes = {
+		CompositeDiscoveryClientTestsConfig.class})
+public class CompositeDiscoveryClientOrderTest {
+
+	@Autowired
+	DiscoveryClient discoveryClient;
+
+	@Test
+	public void shouldGetOrderedDiscoveryClients() {
+		// when:
+		List<DiscoveryClient> discoveryClients = ((CompositeDiscoveryClient) this.discoveryClient)
+				.getDiscoveryClients();
+
+		// then:
+		assertThat(discoveryClients.get(0).description())
+				.isEqualTo(CUSTOM_DISCOVERY_CLIENT);
+		assertThat(discoveryClients.get(1).description())
+				.isEqualTo(DEFAULT_ORDER_DISCOVERY_CLIENT);
+		assertThat(discoveryClients.get(2).description())
+				.isEqualTo("Simple Discovery Client");
+		assertThat(discoveryClients.get(3).description())
+				.isEqualTo(FOURTH_DISCOVERY_CLIENT);
+	}
+
+	@Test
+	public void shouldOnlyReturnServiceInstancesForTheHighestPrecedenceDiscoveryClient() {
+		// when:
+		List<ServiceInstance> serviceInstances = this.discoveryClient
+				.getInstances(CUSTOM_SERVICE_ID);
+
+		// then:
+		assertThat(serviceInstances).hasSize(1);
+		assertThat(serviceInstances.get(0).getPort()).isEqualTo(123);
+	}
+}