Add CompositeAppender.compose(:Appender[]) and CompositeAppender.compose(:Iterable<Appender>) methods to compose an array or Iterable of Appenders.

Resolves gh-73.

spring-geode-starter-logging/src/main/java/org/springframework/geode/logging/slf4j/logback/CompositeAppender.java

@@ -15,6 +15,10 @@
  */
 package org.springframework.geode.logging.slf4j.logback;
 
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+
 import ch.qos.logback.core.Appender;
 import ch.qos.logback.core.AppenderBase;
 import ch.qos.logback.core.Context;
@@ -54,6 +58,52 @@ public class CompositeAppender<T> extends AppenderBase<T> {
 		return one == null ? two : two == null ? one : new CompositeAppender<>(one, two);
 	}
 
+	/**
+	 * Composes an array of {@link Appender Appenders} into a {@link CompositeAppender}.
+	 *
+	 * This operation is null-safe.
+	 *
+	 * @param <T> {@link Class type} of the logging events processed by the {@link Appender Appenders}.
+	 * @param appenders array of {@link Appender Appenders} to compose; may be {@literal null}.
+	 * @return a composition of the array of {@link Appender Appenders}; returns {@literal null} if the array is empty.
+	 * @see #compose(Iterable)
+	 */
+	@SuppressWarnings("unchecked")
+	public static <T> Appender<T> compose(Appender<T>... appenders) {
+
+		List<Appender<T>> resolvedAppenders = appenders != null
+			? Arrays.asList(appenders)
+			: Collections.emptyList();
+
+		return compose(resolvedAppenders);
+
+	}
+
+	/**
+	 * Composes the {@link Iterable} of {@link Appender Appenders} into a {@link CompositeAppender}.
+	 *
+	 * This operation is null-safe.
+	 *
+	 * @param <T> {@link Class type} of the logging events processed by the {@link Appender Appenders}.
+	 * @param appenders {@link Iterable} of {@link Appender Appenders} to compose; may be {@literal null}.
+	 * @return a composition of the {@link Iterable} of {@link Appender Appenders}; returns {@literal null}
+	 * if the {@link Iterable} is {@literal null} or empty.
+	 * @see #compose(Appender, Appender)
+	 * @see java.lang.Iterable
+	 */
+	public static <T> Appender<T> compose(Iterable<Appender<T>> appenders) {
+
+		Appender<T> currentAppender = null;
+
+		appenders = appenders != null ? appenders : Collections::emptyIterator;
+
+		for (Appender<T> appender : appenders) {
+			currentAppender = compose(currentAppender, appender);
+		}
+
+		return currentAppender;
+	}
+
 	/**
 	 * Constructs a new instance of {@link CompositeAppender} composed of {@link Appender} one and {@link Appender} two.
 	 *

spring-geode-starter-logging/src/test/java/org/springframework/geode/logging/slf4j/logback/CompositeAppenderUnitTests.java

@@ -23,6 +23,9 @@ import static org.mockito.Mockito.never;
 import static org.mockito.Mockito.times;
 import static org.mockito.Mockito.verify;
 
+import java.util.Arrays;
+import java.util.Collections;
+
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.mockito.Mock;
@@ -77,6 +80,78 @@ public class CompositeAppenderUnitTests {
 		assertThat(composite.isStarted()).isTrue();
 	}
 
+	@Test
+	public void composeAppenderArray() {
+
+		Appender mockAppenderOne = mock(Appender.class);
+		Appender mockAppenderTwo = mock(Appender.class);
+		Appender mockAppenderThree = mock(Appender.class);
+
+		Appender composite = CompositeAppender.compose(mockAppenderOne, mockAppenderTwo, mockAppenderThree);
+
+		assertThat(composite).isInstanceOf(CompositeAppender.class);
+
+		Appender appenderOne = ((CompositeAppender) composite).getAppenderOne();
+		Appender appenderTwo = ((CompositeAppender) composite).getAppenderTwo();
+
+		assertThat(appenderOne).isInstanceOf(CompositeAppender.class);
+		assertThat(appenderTwo).isEqualTo(mockAppenderThree);
+		assertThat(((CompositeAppender) appenderOne).getAppenderOne()).isEqualTo(mockAppenderOne);
+		assertThat(((CompositeAppender) appenderOne).getAppenderTwo()).isEqualTo(mockAppenderTwo);
+	}
+
+	@Test
+	public void composeAppenderArrayWithOneAppender() {
+		assertThat(CompositeAppender.compose(this.mockAppenderOne)).isSameAs(this.mockAppenderOne);
+	}
+
+	@Test
+	public void composeAppenderArrayWithZeroAppenders() {
+		assertThat(CompositeAppender.compose()).isNull();
+	}
+
+	@Test
+	public void composeAppenderArrayIsNullSafe() {
+		assertThat(CompositeAppender.compose((Appender[]) null)).isNull();
+	}
+
+	@Test
+	public void composeAppenderIterable() {
+
+		Appender mockAppenderOne = mock(Appender.class);
+		Appender mockAppenderTwo = mock(Appender.class);
+		Appender mockAppenderThree = mock(Appender.class);
+
+		Appender composite =
+			CompositeAppender.compose(Arrays.asList(mockAppenderOne, mockAppenderTwo, mockAppenderThree));
+
+		assertThat(composite).isInstanceOf(CompositeAppender.class);
+
+		Appender appenderOne = ((CompositeAppender) composite).getAppenderOne();
+		Appender appenderTwo = ((CompositeAppender) composite).getAppenderTwo();
+
+		assertThat(appenderOne).isInstanceOf(CompositeAppender.class);
+		assertThat(appenderTwo).isEqualTo(mockAppenderThree);
+		assertThat(((CompositeAppender) appenderOne).getAppenderOne()).isEqualTo(mockAppenderOne);
+		assertThat(((CompositeAppender) appenderOne).getAppenderTwo()).isEqualTo(mockAppenderTwo);
+	}
+
+	@Test
+	public void composeAppenderIterableWithOneAppender() {
+		assertThat(CompositeAppender.compose(Collections.singletonList(this.mockAppenderTwo)))
+			.isSameAs(this.mockAppenderTwo);
+	}
+
+	@Test
+	public void composeAppenderIterableWithZeroAppenders() {
+		assertThat(CompositeAppender.compose(Collections.emptyList())).isNull();
+	}
+
+	@Test
+	public void composeAppenderIterableIsNullSafe() {
+		assertThat(CompositeAppender.compose((Iterable<Appender<Object>>) null)).isNull();
+	}
+
 	@Test
 	public void setContextConfiguresContextOnCompositeAppenderAndComposedAppenders() {