Can a web service return a stream?

Question

I\'ve been writing a little application that will let people upload & download files to me. I\'ve added a web service to this applciation to provide the upload/download fun

Answer 1

One way to do it is to add a uploadFileChunk(byte[] chunkData, int size, int offset, int totalSize) method (or something like that) that uploads parts of the file and the servers writes it the to disk.

Answer 2

The RMIIO library for Java provides for handing a RemoteInputStream across RMI - we only needed RMI, though you should be able to adapt the code to work over other types of RMI . This may be of help to you - especially if you can have a small application on the user side. The library was developed with the express purpose of being able to limit the size of the data pushed to the server to avoid exactly the type of situation you describe - effectively a DOS attack by filling up ram or disk.

With the RMIIO library, the server side gets to decide how much data it is willing to pull, where with HTTP PUT and POSTs, the client gets to make that decision, including the rate at which it pushes.

Answer 3

Yes, a webservice can do streaming. I created a webservice using Apache Axis2 and MTOM to support rendering PDF documents from XML. Since the resulting files could be quite large, streaming was important because we didn't want to keep it all in memory. Take a look at Oracle's documentation on streaming SOAP attachments.

Alternately, you can do it yourself, and tomcat will create the Chunked headers. This is an example of a spring controller function that streams.

 @RequestMapping(value = "/stream")
        public void hellostreamer(HttpServletRequest request, HttpServletResponse response) throws CopyStreamException, IOException  
{

            response.setContentType("text/xml");
            OutputStreamWriter writer = new OutputStreamWriter (response.getOutputStream());
            writer.write("this is streaming");
            writer.close();

    }

Answer 4

Stephen Denne has a Metro implementation that satisfies your requirement. My answer is provided below after a short explination as to why that is the case.

Most Web Service implementations that are built using HTTP as the message protocol are REST compliant, in that they only allow simple send-receive patterns and nothing more. This greatly improves interoperability, as all the various platforms can understand this simple architecture (for instance a Java web service talking to a .NET web service).

If you want to maintain this you could provide chunking.

boolean uploadFile(String username, String password, String fileName, int currentChunk, int totalChunks, byte[] chunk);

This would require some footwork in cases where you don't get the chunks in the right order (Or you can just require the chunks come in the right order), but it would probably be pretty easy to implement.

Answer 5

For WCF I think its possible to define a member on a message as stream and set the binding appropriately - I've seen this work with wcf talking to Java web service.

You need to set the transferMode="StreamedResponse" in the httpTransport configuration and use mtomMessageEncoding (need to use a custom binding section in the config).

I think one limitation is that you can only have a single message body member if you want to stream (which kind of makes sense).

Answer 6

I think using a simple servlet for this task would be a much easier approach, or is there any reason you can not use a servlet?

For instance you could use the Commons open source library.