[GitHub] [druid] gianm commented on a diff in pull request #14200: Ability to optionally bind extra service dimensions to ServiceEvents

["gianm (via GitHub)" <gi...@apache.org>]

gianm commented on code in PR #14200:
URL: https://github.com/apache/druid/pull/14200#discussion_r1183225680


##########
server/src/main/java/org/apache/druid/server/emitter/ExtraServiceDimensions.java:
##########
@@ -29,12 +29,25 @@
 
 /**
  * Annotation to inject extra dimensions, added to all events, emitted via {@link EmitterModule#getServiceEmitter}.
- *
+ * <p/>
  * For example, write this in a body of {@link com.google.inject.Module#configure} of your extension module):
- *
+ * <p/>
  * MapBinder<String, String> extraDims =
  *     MapBinder.newMapBinder(binder, String.class, String.class, ExtraServiceDimensions.class);
  * extraDims.addBinding("foo").toInstance("bar");
+ * <p/>
+ * If a module wishes to optionally bind service dimensions they may do so by using the binding to
+ * Map<String, Optional<String>. The key is only added to the service dimensions that are emitted if the Optional is
+ * present.
+ * <p/>
+ * MapBinder<String, Optional<String>> extraDims =
+ *     MapBinder.newMapBinder(
+ *        binder,
+ *        new TypeLiteral<String>() {},
+ *        new TypeLiteral<Optional<String>>() {},
+ *        ExtraServiceDimensions.class
+ * );
+ * extraDims.addBinding("foo").toInstance(Optional.fromNullable(bar));

Review Comment:
   What's the advantage of doing this, vs. keeping `String` -> `String` and having modules avoid calling `addBinding` if `bar` is null?



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