add bodyStream method for Client in case when SDK used to download big files.

Author: jemygraw

src/main/java/com/qiniu/http/Response.java

@@ -8,6 +8,7 @@
 import okhttp3.MediaType;
 
 import java.io.IOException;
+import java.io.InputStream;
 import java.util.Locale;
 
 /**
@@ -198,6 +199,13 @@ public String bodyString() throws QiniuException {
         return StringUtils.utf8String(body());
     }
 
+    public synchronized InputStream bodyStream() throws QiniuException {
+        if (this.response == null) {
+            return null;
+        }
+        return this.response.body().byteStream();
+    }
+
     public String contentType() {
         return ctype(response);
     }