jersey - StreamingOutput as Response entity

Try invoking outputStream.flush() from the method FeedReturnStreamingOutput.write(...) every X number of bytes written to the output stream or something like that.

I guess the buffer of the connection is not filled with the data you are returning. So the service does not return anything until Jersey invokes outputStream.close().

In my case, I have a service that streams data and I am doing it exactly as you: by returning Response.ok(<instance of StreamingOutput>).build();.

My service returns data from a database and I invoke outputStream.flush() after writing each row to the output stream.

I know that the service streams data because I can see the client begins receiving data before the service has finished sending the entire result.

The problem is the buffering OutputStream that Jersey uses to buffer the entity in order to determine the Content-Length header. The size of the buffer default to 8 kb. You disable the buffering if you want, or just change the size of the buffer, with the property

ServerProperties.OUTBOUND_CONTENT_LENGTH_BUFFER

An integer value that defines the buffer size used to buffer server-side response entity in order to determine its size and set the value of HTTP "Content-Length" header.

If the entity size exceeds the configured buffer size, the buffering would be cancelled and the entity size would not be determined. Value less or equal to zero disable the buffering of the entity at all.

This property can be used on the server side to override the outbound message buffer size value - default or the global custom value set using the "jersey.config.contentLength.buffer" global property.

The default value is 8192.

Here's an example

@Path("streaming")
public class StreamingResource {

    @GET
    @Produces("application/octet-stream")
    public Response getStream() {
        return Response.ok(new FeedReturnStreamingOutput()).build();
    }

    public static class FeedReturnStreamingOutput implements StreamingOutput {

        @Override
        public void write(OutputStream output)
                throws IOException, WebApplicationException {
            try {
                for (int i = 0; i < 10; i++) {
                    output.write(String.format("Hello %d\n", i).getBytes());
                    output.flush();
                    TimeUnit.MILLISECONDS.sleep(500);
                }
            } catch (InterruptedException e) {  throw new RuntimeException(e); }
        }
    }
}

Here's the result without setting the property

And here's the result after setting the property value to 0

public class AppConfig extends ResourceConfig {
    public AppConfig() {
        ...
        property(ServerProperties.OUTBOUND_CONTENT_LENGTH_BUFFER, 0);
    }
}

Either your response is too small and never gets chunked so the server flushes the entire request at once. Or you have a server side issue were your jax-rs library is awaiting to have the complete stream before flushing.

However this looks more like a client problem. And you seem to be using an old version of jersey-client.

Also that .get(ClientResponse.class) looks fishy.

Try using the JAX-RS standard as it is today (at least in the client):

import javax.ws.rs.client.Client;
import javax.ws.rs.client.ClientBuilder;
import javax.ws.rs.client.WebTarget;
import javax.ws.rs.core.Response;

Client client = ClientBuilder.newBuilder().build();
WebTarget target = client.target("http://localhost:8080/");
Response response = target.path("path/to/resource").request().get();

While having jersey client 2.17 in the classpath:

<dependency>
    <groupId>org.glassfish.jersey.core</groupId>
    <artifactId>jersey-client</artifactId>
    <version>2.17</version>
</dependency>