Btukfyl

My Setup: I have created a REST service (Jersey/Dropwizard) that streams large content from a database. During a GET operation, the service taps into the database through a connection pool, wraps the data into a stream and performs some on-the-fly transformation to render the requested data in various encodings (CSV, JSON, ...). The life time of the database connection is tied to the life time of the stream and only when the stream is closed, the database connection is released.

The stream transformation is performed by an Encoder class that returns a StreamingOutput which is then passed to the Response object. The Encoder currently handles resource closing when the stream is fully consumed.

My Problem: Since StreamingOutput does not implement AutoCloseable, connection leaks may occur when the output is only partially consumed.

I sometimes observe that stale active connections are piling up in the connection pool, and I suspect that they arise from aborted HTTP connections. As you can see below, the current code handles exceptions that occur in the try block. What I cannot handle are Exceptions that occur after the return statement and I don't know how to attach any instructions for resource closing to the Response object.

My Question: How can I inform the Response object to close particular resources after the request has terminated (regularly or due to an error)? Or: Is there a better way to safely close any associated resources when the request context ends?

 @GET

 //@Produces(...)

 public Response streamData(

        @PathParam("key") String key,

        // ... other params

        ) {



    //decode and validate params

    Stream<Pojo> ps = null;

    try {

        // connect to db and obtain data stream for <key>

        ps = loadData(db, key);

        // apply detailed encoding instrunctions and create a StreamingOutput

        final StreamingOutput stream = Encoder.encodeData(ps, encodingArgs);

        return Response.ok(stream).build();

    } catch (Exception e) {

        closeOnException(ps); // wrapper for ps.close();

        throw e;

    }

 }

You can add to your method HttpServletResponse:

@Produces(MediaType.APPLICATION_OCTET_STREAM)

public Object streamData(

            @PathParam("key") String key,

            @Context HttpServletResponse response,

            // ... other params

            ) {

  ...

  response.getOutputStream().write(....)

  response.flushBuffer();

  response.getOutputStream().close();

  return null;

}