Refactor ActivityTaskExecutor to use ActivityTask interface (#897)

* Refactor ActivityTaskExecutor to use ActivityTask interface

* lint

Author: shijiesheng

src/main/java/com/uber/cadence/activity/ActivityTask.java

@@ -65,4 +65,6 @@ public interface ActivityTask {
   String getWorkflowDomain();
 
   int getAttempt();
+
+  byte[] getInput();
 }

src/main/java/com/uber/cadence/internal/sync/POJOActivityTaskHandler.java

@@ -24,6 +24,7 @@
 import com.uber.cadence.RespondActivityTaskCompletedRequest;
 import com.uber.cadence.RespondActivityTaskFailedRequest;
 import com.uber.cadence.activity.ActivityMethod;
+import com.uber.cadence.activity.ActivityTask;
 import com.uber.cadence.client.ActivityCancelledException;
 import com.uber.cadence.common.MethodRetry;
 import com.uber.cadence.converter.DataConverter;
@@ -201,7 +202,7 @@ public Result handle(
   }
 
   interface ActivityTaskExecutor {
-    ActivityTaskHandler.Result execute(ActivityTaskImpl task, Scope metricsScope);
+    ActivityTaskHandler.Result execute(ActivityTask task, Scope metricsScope);
   }
 
   private class POJOActivityImplementation implements ActivityTaskExecutor {
@@ -214,7 +215,7 @@ private class POJOActivityImplementation implements ActivityTaskExecutor {
     }
 
     @Override
-    public ActivityTaskHandler.Result execute(ActivityTaskImpl task, Scope metricsScope) {
+    public ActivityTaskHandler.Result execute(ActivityTask task, Scope metricsScope) {
       ActivityExecutionContext context =
           new ActivityExecutionContextImpl(service, domain, task, dataConverter, heartbeatExecutor);
       byte[] input = task.getInput();
@@ -250,7 +251,7 @@ private class POJOLocalActivityImplementation implements ActivityTaskExecutor {
     }
 
     @Override
-    public ActivityTaskHandler.Result execute(ActivityTaskImpl task, Scope metricsScope) {
+    public ActivityTaskHandler.Result execute(ActivityTask task, Scope metricsScope) {
       ActivityExecutionContext context =
           new LocalActivityExecutionContextImpl(service, domain, task);
       CurrentActivityExecutionContext.set(context);