GH-618: Add StreamsBuilderFBean#getStreamsConfig

Resolves #618

While the `StreamsBuilderFactoryBean` requires a `StreamsConfig` to
function, it has the ability to add a `StreamsConfig` after creation, so
it's technically possible that it could return `null`.

* Fix typo in `StreamsBuilderFactoryLateConfigTests`

Author: zacholauson

spring-kafka/src/main/java/org/springframework/kafka/core/StreamsBuilderFactoryBean.java

@@ -28,6 +28,7 @@
 import org.springframework.beans.factory.config.AbstractFactoryBean;
 import org.springframework.context.SmartLifecycle;
 import org.springframework.kafka.KafkaException;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
 /**
@@ -37,6 +38,7 @@
  * @author Artem Bilan
  * @author Ivan Ursul
  * @author Soby Chacko
+ * @author Zach Olauson
  *
  * @since 1.1.4
  */
@@ -128,6 +130,11 @@ public void setStreamsConfig(StreamsConfig streamsConfig) {
 		this.streamsConfig = streamsConfig;
 	}
 
+	@Nullable
+	public StreamsConfig getStreamsConfig() {
+		return this.streamsConfig;
+	}
+
 	public void setClientSupplier(KafkaClientSupplier clientSupplier) {
 		Assert.notNull(clientSupplier, "'clientSupplier' must not be null");
 		this.clientSupplier = clientSupplier; // NOSONAR (sync)

spring-kafka/src/test/java/org/springframework/kafka/core/StreamsBuilderFactoryLateConfigTests.java

@@ -55,7 +55,7 @@ public class StreamsBuilderFactoryLateConfigTests {
 	private StreamsBuilderFactoryBean streamsBuilderFactoryBean;
 
 	@Test(expected = KafkaException.class)
-	public void testStreamBuilderFactoryCannotBeStartedWithoutStreamconfig() {
+	public void testStreamBuilderFactoryCannotBeStartedWithoutStreamsConfig() {
 		StreamsBuilderFactoryBean streamsBuilderFactoryBean = new StreamsBuilderFactoryBean();
 		streamsBuilderFactoryBean.start();
 	}