Closing OutputStream before calling toByteArray on the underlying ByteArrayOutputStream

gistfile1.txt

When a `DataOutputStream` or an `ObjectOutputStream` instance wraps an underlying ByteArrayOutputStream instance,
it is recommended to flush or close the DataOutputStream and ObjectOutputStream before invoking the 
underlying instances's toByteArray(). Also, it is a good practice to call flush/close explicitly 
as mentioned for example [here] (http://stackoverflow.com/questions/2984538/how-to-use-bytearrayoutputstream-and-dataoutputstream-simultaneously-java).
This pull request adds a `flush` method before calling toByteArray().