workaround solution for SageMaker (#2405)

Author: lxning

frontend/archive/src/main/java/org/pytorch/serve/archive/model/ModelArchive.java

@@ -80,15 +80,28 @@ public static ModelArchive downloadModel(
             }
         }
 
-        if (new File(url).isDirectory()) {
+        File directory = new File(url);
+        if (directory.isDirectory()) {
             // handle the case that the input url is a directory.
             // the input of url is "/xxx/model_store/modelXXX" or
             // "xxxx/yyyyy/modelXXX".
-            return load(url, new File(url), false);
+            File[] fileList = directory.listFiles();
+            if (fileList.length == 1 && fileList[0].isDirectory()) {
+                // handle the case that a model tgz file
+                // has root dir after decompression on SageMaker
+                return load(url, fileList[0], false);
+            }
+            return load(url, directory, false);
         } else if (modelLocation.exists()) {
             // handle the case that "/xxx/model_store/modelXXX" is directory.
             // the input of url is modelXXX when torchserve is started
             // with snapshot or with parameter --models modelXXX
+            File[] fileList = modelLocation.listFiles();
+            if (fileList.length == 1 && fileList[0].isDirectory()) {
+                // handle the case that a model tgz file
+                // has root dir after decompression on SageMaker
+                return load(url, fileList[0], false);
+            }
             return load(url, modelLocation, false);
         }