GAE Blobstore IllegalStateException：无内容

Question

When attempting to serve a file from the blobstore via BlobstoreService.serve(key, res), I get the following error:

WARNING: /path/to/servlet
java.lang.IllegalStateException: NO CONTENT
at org.mortbay.jetty.HttpGenerator.addContent(HttpGenerator.java:106)
at org.mortbay.jetty.AbstractGenerator$Output.write(AbstractGenerator.java:644)
at org.mortbay.jetty.AbstractGenerator$Output.write(AbstractGenerator.java:579)
at com.google.appengine.api.blobstore.dev.ServeBlobFilter.copy(ServeBlobFilter.java:129)
at com.google.appengine.api.blobstore.dev.ServeBlobFilter.serveBlob(ServeBlobFilter.java:185)
at com.google.appengine.api.blobstore.dev.ServeBlobFilter.doFilter(ServeBlobFilter.java:64)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:43)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.tools.development.StaticFileFilter.doFilter(StaticFileFilter.java:125)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.tools.development.BackendServersFilter.doFilter(BackendServersFilter.java:97)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:388)
at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)
at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:418)
at com.google.appengine.tools.development.DevAppEngineWebAppContext.handle(DevAppEngineWebAppContext.java:94)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at com.google.appengine.tools.development.JettyContainerService$ApiProxyHandler.handle(JettyContainerService.java:370)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at org.mortbay.jetty.Server.handle(Server.java:326)
at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
at org.mortbay.jetty.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:923)
at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:547)
at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:212)
at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:409)
at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:582)

If I attempt to download from this URL using a browser, the browser stores a file of size 0 bytes. I am testing this on the dev server from SDK 1.7.1.

I am using Jersey to create the REST API, which seems to be causing the problem. If I create a regular servlet, it serves the file properly. I wonder whether this is an issue with using the @GET annotation, which requires that the function return something. However, if I return anything, the blobstore complains and tells me that it has been preempted by data that has already been sent.

The service doesn't even seem to be sending any headers back in response to a request.

Here is the code that is supposed to send the response:

@GET
public void getAirport(@PathParam(APIUtils.VERSION_NAME) String versionName, @Context HttpServletResponse res) throws IOException {
    BlobstoreService blobstoreService = BlobstoreServiceFactory.getBlobstoreService();

    DataDAO dao = new DataDAO();
    BlobKey key = dao.getAirportBlobKey(versionName);

    if(key == null) {
        res.sendError(HttpServletResponse.SC_NOT_FOUND, "No airport record found for: " + versionName);
    }
    else {
        blobstoreService.serve(key, res);
    }
}

Any ideas?

Answer 1

I haven't found any documentation to explain this behavior, but I was able to fix my problem. The following seems to be a solution:

blobstoreService.serve(key, res);
return Response.created(null).status(HttpServletResponse.SC_OK).build();

Since the body of the response is null , is doesn't interfere with the blobstore serving the blob. I'd still like to know some more about the inner workings when Jersey processes the @GET annotation, but at least this works for now.