Extract constant functions when used in match to reduce number of allocations. (#1336)

* Extract constant functions when used in match to reduce number of allocations.

* Fix names for non-constant functions. Fix deprecated warnings.

* Add more optimization and clean zipkin exporter.

* Use correct name format for RETURN_STRING.

* Fix formatting.

* Fix import for Nullable.

1 files changed, 13 insertions, 18 deletions

diff --git a/contrib/zpages/src/main/java/io/opencensus/contrib/zpages/TracezZPageHandler.java b/contrib/zpages/src/main/java/io/opencensus/contrib/zpages/TracezZPageHandler.java
index b0cf579c..8c1aedae 100644
--- a/contrib/zpages/src/main/java/io/opencensus/contrib/zpages/TracezZPageHandler.java
+++ b/contrib/zpages/src/main/java/io/opencensus/contrib/zpages/TracezZPageHandler.java
@@ -672,27 +672,22 @@ final class TracezZPageHandler extends ZPageHandler {
     return stringBuilder.toString();
   }
 
+  // The return type needs to be nullable when this function is used as an argument to 'match' in
+  // attributeValueToString, because 'match' doesn't allow covariant return types.
+  private static final Function<Object, /*@Nullable*/ String> returnToString =
+      new Function<Object, /*@Nullable*/ String>() {
+        @Override
+        public String apply(Object input) {
+          return input.toString();
+        }
+      };
+
   @javax.annotation.Nullable
   private static String attributeValueToString(AttributeValue attributeValue) {
     return attributeValue.match(
-        new Function<String, /*@Nullable*/ String>() {
-          @Override
-          public String apply(String stringValue) {
-            return stringValue;
-          }
-        },
-        new Function<Boolean, /*@Nullable*/ String>() {
-          @Override
-          public String apply(Boolean booleanValue) {
-            return booleanValue.toString();
-          }
-        },
-        new Function<Long, /*@Nullable*/ String>() {
-          @Override
-          public String apply(Long longValue) {
-            return longValue.toString();
-          }
-        },
+        returnToString,
+        returnToString,
+        returnToString,
         Functions.</*@Nullable*/ String>returnNull());
   }