Support positional RetryListeners

- useful when framework code needs to add a listener before user
  listeners.

src/main/java/org/springframework/retry/support/RetryTemplate.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2019 the original author or authors.
+ * Copyright 2006-2020 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.
@@ -143,16 +143,41 @@ public class RetryTemplate implements RetryOperations {
 	}
 
 	/**
-	 * Register an additional listener.
+	 * Register an additional listener at the end of the list.
 	 * @param listener the {@link RetryListener}
 	 * @see #setListeners(RetryListener[])
 	 */
 	public void registerListener(RetryListener listener) {
+		registerListener(listener, this.listeners.length);
+	}
+
+	/**
+	 * Register an additional listener at the specified index.
+	 * @param listener the {@link RetryListener}
+	 * @param index the position in the list.
+	 * @since 1.3
+	 * @see #setListeners(RetryListener[])
+	 */
+	public void registerListener(RetryListener listener, int index) {
 		List<RetryListener> list = new ArrayList<RetryListener>(Arrays.asList(this.listeners));
-		list.add(listener);
+		if (index >= list.size()) {
+			list.add(listener);
+		}
+		else {
+			list.add(index, listener);
+		}
 		this.listeners = list.toArray(new RetryListener[list.size()]);
 	}
 
+	/**
+	 * Return true if at least one listener is registered.
+	 * @return true if listeners present.
+	 * @since 1.3
+	 */
+	public boolean hasListeners() {
+		return this.listeners.length > 0;
+	}
+
 	/**
 	 * Setter for {@link BackOffPolicy}.
 	 * @param backOffPolicy the {@link BackOffPolicy}

src/test/java/org/springframework/retry/interceptor/RetryOperationsInterceptorTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2019 the original author or authors.
+ * Copyright 2006-2020 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.
@@ -22,10 +22,13 @@ import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.atomic.AtomicBoolean;
+
 import org.aopalliance.intercept.MethodInterceptor;
 import org.aopalliance.intercept.MethodInvocation;
 import org.junit.Before;
 import org.junit.Test;
+
 import org.springframework.aop.framework.Advised;
 import org.springframework.aop.framework.ProxyFactory;
 import org.springframework.aop.target.SingletonTargetSource;
@@ -43,6 +46,7 @@ import org.springframework.util.ClassUtils;
 
 import static org.hamcrest.core.IsEqual.equalTo;
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertThat;
 import static org.junit.Assert.assertTrue;
@@ -66,13 +70,34 @@ public class RetryOperationsInterceptorTests {
 	public void setUp() throws Exception {
 		this.interceptor = new RetryOperationsInterceptor();
 		RetryTemplate retryTemplate = new RetryTemplate();
+		final AtomicBoolean calledFirst = new AtomicBoolean();
 		retryTemplate.registerListener(new RetryListenerSupport() {
+
+			@Override
+			public <T, E extends Throwable> boolean open(RetryContext context, RetryCallback<T, E> callback) {
+
+				calledFirst.set(true);
+				return true;
+
+			}
+
 			@Override
 			public <T, E extends Throwable> void close(RetryContext context, RetryCallback<T, E> callback,
 					Throwable throwable) {
 				RetryOperationsInterceptorTests.this.context = context;
 			}
+
 		});
+		retryTemplate.registerListener(new RetryListenerSupport() {
+
+			@Override
+			public <T, E extends Throwable> boolean open(RetryContext context, RetryCallback<T, E> callback) {
+
+				assertFalse(calledFirst.get());
+				return true;
+			}
+
+		}, 0);
 		this.interceptor.setRetryOperations(retryTemplate);
 		this.target = new ServiceImpl();
 		this.service = ProxyFactory.getProxy(Service.class, new SingletonTargetSource(this.target));