Fix Map Lookup Introspection Endpoints and update doc for Globally Ca…

…ched Lookups (apache#17436)

Map Lookup Introspection API endpoints /keys and /values no longer return an invalid JSON object.
Also, update documentation to clarify the version returned by the /version introspection endpoint.

---------

Co-authored-by: Ashwin Tumma <ashwin.tumma@salesforce.com>

docs/querying/lookups-cached-global.md

@@ -384,4 +384,4 @@ The JDBC lookups will poll a database to populate its local cache. If the `tsCol
 
 ## Introspection
 
-Globally cached lookups have introspection points at `/keys` and `/values` which return a complete set of the keys and values (respectively) in the lookup. Introspection to `/` returns the entire map. Introspection to `/version` returns the version indicator for the lookup.
+Globally cached lookups have introspection points at `/keys` and `/values`, which return the complete set of keys and values respectively in the lookup as a JSON object. Introspection to `/` returns the entire map as a JSON object. Introspection to `/version` provides the internal version indicating when the lookup cache was last updated. See [Introspect A Lookup](./lookups.md#Introspect a Lookup) for examples.

server/src/main/java/org/apache/druid/query/lookup/MapLookupExtractorFactory.java

@@ -145,15 +145,15 @@ public MapLookupIntrospectionHandler(Map<String, String> map)
     @Produces(MediaType.APPLICATION_JSON)
     public Response getKeys()
     {
-      return Response.ok(map.keySet().toString()).build();
+      return Response.ok(map.keySet()).build();
     }
 
     @GET
     @Path("/values")
     @Produces(MediaType.APPLICATION_JSON)
     public Response getValues()
     {
-      return Response.ok(map.values().toString()).build();
+      return Response.ok(map.values()).build();
     }
 
     @GET

server/src/test/java/org/apache/druid/query/lookup/LookupIntrospectionResourceTest.java

@@ -152,7 +152,7 @@ public void testGetKey()
                                  .accept(MediaType.APPLICATION_JSON)
                                  .get(ClientResponse.class);
     String s = resp.getEntity(String.class);
-    Assert.assertEquals("[key, key2]", s);
+    Assert.assertEquals("[\"key\",\"key2\"]", s);
     Assert.assertEquals(200, resp.getStatus());
   }
 
@@ -166,7 +166,7 @@ public void testGetValue()
                                  .accept(MediaType.APPLICATION_JSON)
                                  .get(ClientResponse.class);
     String s = resp.getEntity(String.class);
-    Assert.assertEquals("[value, value2]", s);
+    Assert.assertEquals("[\"value\",\"value2\"]", s);
     Assert.assertEquals(200, resp.getStatus());
   }