INT-4477: Add getRole() to LeaderInitiator Context

JIRA: https://jira.spring.io/browse/INT-4477

When running multiple roles, it is useful to be able to determine the
role for a particular context, e.g. in an event.

* Docs

**cherry-pick to 5.0.x**

(cherry picked from commit 73dbdb8)

spring-integration-zookeeper/src/main/java/org/springframework/integration/zookeeper/leader/LeaderInitiator.java

@@ -47,8 +47,6 @@ public class LeaderInitiator implements SmartLifecycle {
 
 	private static final String DEFAULT_NAMESPACE = "/spring-integration/leader/";
 
-	private static final Context NULL_CONTEXT = () -> false;
-
 	private final CuratorContext context = new CuratorContext();
 
 	/**
@@ -61,6 +59,20 @@ public class LeaderInitiator implements SmartLifecycle {
 	 */
 	private final Candidate candidate;
 
+	private final Context nullContext = new Context() {
+
+		@Override
+		public boolean isLeader() {
+			return false;
+		}
+
+		@Override
+		public String getRole() {
+			return LeaderInitiator.this.candidate.getRole();
+		}
+
+	};
+
 	private final Object lifecycleMonitor = new Object();
 
 	/**
@@ -203,13 +215,13 @@ public class LeaderInitiator implements SmartLifecycle {
 	}
 
 	/**
-	 * The context of the initiator or null if not running.
-	 * @return the context (or null if not running)
+	 * The context of the initiator.
+	 * @return the context.
 	 * @since 5.0
 	 */
 	public Context getContext() {
 		if (this.leaderSelector == null) {
-			return NULL_CONTEXT;
+			return nullContext;
 		}
 		return this.context;
 	}
@@ -292,6 +304,11 @@ public class LeaderInitiator implements SmartLifecycle {
 			LeaderInitiator.this.leaderSelector.interruptLeadership();
 		}
 
+		@Override
+		public String getRole() {
+			return LeaderInitiator.this.candidate.getRole();
+		}
+
 		@Override
 		public String toString() {
 			return "CuratorContext{role=" + LeaderInitiator.this.candidate.getRole() +

spring-integration-zookeeper/src/test/java/org/springframework/integration/zookeeper/config/LeaderInitiatorFactoryBeanTests.java

@@ -16,6 +16,7 @@
 
 package org.springframework.integration.zookeeper.config;
 
+import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.instanceOf;
 import static org.junit.Assert.assertThat;
 import static org.junit.Assert.assertTrue;
@@ -91,7 +92,7 @@ public class LeaderInitiatorFactoryBeanTests extends ZookeeperTestSupport {
 	public void testExceptionFromEvent() throws Exception {
 		CountDownLatch onGranted = new CountDownLatch(1);
 
-		LeaderInitiator initiator = new LeaderInitiator(client, new DefaultCandidate());
+		LeaderInitiator initiator = new LeaderInitiator(client, new DefaultCandidate("foo", "bar"));
 
 		initiator.setLeaderEventPublisher(new DefaultLeaderEventPublisher() {
 
@@ -107,10 +108,12 @@ public class LeaderInitiatorFactoryBeanTests extends ZookeeperTestSupport {
 
 		});
 
+		assertThat(initiator.getContext().getRole(), equalTo("bar"));
 		initiator.start();
 
 		assertTrue(onGranted.await(10, TimeUnit.SECONDS));
 		assertTrue(initiator.getContext().isLeader());
+		assertThat(initiator.getContext().getRole(), equalTo("bar"));
 
 		initiator.stop();
 	}