add customizer interface for spring boot integration

This to allow customization of the client, without having to manually create the client.

Author: koenpunt

analytics-spring-boot-starter/src/main/java/com/segment/analytics/autoconfigure/SegmentAnalyticsAutoConfiguration.java

@@ -2,6 +2,7 @@
 
 import com.segment.analytics.Analytics;
 import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.beans.factory.ObjectProvider;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
 import org.springframework.boot.context.properties.EnableConfigurationProperties;
 import org.springframework.context.annotation.Bean;
@@ -20,7 +21,9 @@ public class SegmentAnalyticsAutoConfiguration {
   @Autowired private SegmentProperties properties;
 
   @Bean
-  public Analytics segmentAnalytics() {
-    return Analytics.builder(properties.getWriteKey()).build();
+  public Analytics segmentAnalytics(ObjectProvider<SegmentAnalyticsCustomizer> customizerProvider) {
+    Analytics.Builder builder = Analytics.builder(properties.getWriteKey());
+    customizerProvider.orderedStream().forEach((customizer) -> customizer.customize(builder));
+    return builder.build();
   }
 }

analytics-spring-boot-starter/src/main/java/com/segment/analytics/autoconfigure/SegmentAnalyticsCustomizer.java

@@ -0,0 +1,21 @@
+package com.segment.analytics.autoconfigure;
+
+import com.segment.analytics.Analytics;
+
+/**
+ * Callback interface that can be used to customize a
+ * {@link com.segment.analytics.Analytics.Builder Analytics.Builder}.
+ *
+ * @author Koen Punt
+ */
+@FunctionalInterface
+public interface SegmentAnalyticsCustomizer {
+
+    /**
+     * Callback to customize a
+     * {@link com.segment.analytics.Analytics.Builder Analytics.Builder} instance.
+     * @param analyticsBuilder the analytics builder to customize
+     */
+    void customize(Analytics.Builder analyticsBuilder);
+
+}