Add a close method for workflow client (#345)

Author: Liang Mei

src/main/java/com/uber/cadence/client/WorkflowClient.java

@@ -46,7 +46,7 @@
  * and then calling a method annotated with {@literal @}{@link WorkflowMethod}.
  *
  * <pre><code>
- * WorkflowClient workflowClient = WorkflowClient.newClient(cadenceServiceHost, cadenceServicePort, domain);
+ * WorkflowClient workflowClient = WorkflowClient.newInstance(cadenceServiceHost, cadenceServicePort, domain);
  * // Create a workflow stub.
  * FileProcessingWorkflow workflow = workflowClient.newWorkflowStub(FileProcessingWorkflow.class);
  * </code></pre>
@@ -728,4 +728,9 @@ static <A1, A2, A3, A4, A5, A6, R> CompletableFuture<R> execute(
       A6 arg6) {
     return WorkflowClientInternal.execute(workflow, arg1, arg2, arg3, arg4, arg5, arg6);
   }
+
+  /**
+   * Closes the workflow client and the underlying IWorkflowService when this method is called.
+   */
+  void close();
 }

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

@@ -50,6 +50,7 @@ public final class WorkflowClientInternal implements WorkflowClient {
   private final ManualActivityCompletionClientFactory manualActivityCompletionClientFactory;
   private final DataConverter dataConverter;
   private final WorkflowClientInterceptor[] interceptors;
+  private final IWorkflowService workflowService;
 
   /**
    * Creates worker that connects to the local instance of the Cadence Service that listens on a
@@ -130,6 +131,7 @@ private WorkflowClientInternal(
     if (options == null) {
       options = new WorkflowClientOptions.Builder().build();
     }
+    this.workflowService = service;
     this.genericClient =
         new GenericWorkflowClientExternalImpl(service, domain, options.getMetricsScope());
     this.dataConverter = options.getDataConverter();
@@ -449,4 +451,9 @@ public static <A1, A2, A3, A4, A5, A6, R> CompletableFuture<R> execute(
       A6 arg6) {
     return execute(() -> workflow.apply(arg1, arg2, arg3, arg4, arg5, arg6));
   }
+
+  @Override
+  public void close() {
+    this.workflowService.close();
+  }
 }