Getting InputStream with RestTemplate

Question

I am using URL class to read an InputStream from it. Is there any way I can use RestTemplate for this?

InputStream input = new URL(url).openStream();
JsonReader reader = new JsonReader(new InputStreamReader(input, StandardCharsets.UTF_8.displayName())); 

How can I get InputStream with RestTemplate instead of using URL?

Answer 1

You should not get the InputStream directly. RestTemplate is meant to encapsulate processing the response (and request) content. Its strength is handling all the IO and handing you a ready-to-go Java object.

One of RestTemplate's original authors, Brian Clozel, has stated:

RestTemplate is not meant to stream the response body; its contract doesn't allow it, and it's been around for so long that changing such a basic part of its behavior cannot be done without disrupting many applications.

You'll need to register appropriate HttpMessageConverter objects. Those will have access to the response's InputStream, through an HttpInputMessage object.

As Abdull suggests, Spring does come with an HttpMessageConverter implementation for Resource which itself wraps an InputStream, ResourceHttpMessageConverter. It doesn't support all Resource types, but since you should be programming to interfaces anyway, you should just use the superinterface Resource.

The current implementation (4.3.5), will return a ByteArrayResource with the content of the response stream copied to a new ByteArrayInputStream which you can access.

You don't have to close the stream. The RestTemplate takes care of that for you. (This is unfortunate if you try to use a InputStreamResource, another type supported by the ResourceHttpMessageConverter, because it wraps the underlying response's InputStream but is closed before it can be exposed to your client code.)