gianm commented on code in PR #14200:
URL: https://github.com/apache/druid/pull/14200#discussion_r1183225680
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server/src/main/java/org/apache/druid/server/emitter/ExtraServiceDimensions.java:
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@@ -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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