Why I can still send data after the response is co

Question

I use the following REST handler to transfer a file to client.

I deliberately called response.flushBuffer() in hope that I should be blocked from writing to the response since it is already committed. And I expect client will not receive the full file.

But the whole file still gets sent to client. And no exception about Response Already Committed is thrown.

Why?

My code:

@RestController
public class ChunkedTransferAPI {

    @Autowired
    ServletContext servletContext;

    @RequestMapping(value = "bootfile.efi", method = { RequestMethod.GET, RequestMethod.HEAD })
    public void doHttpBoot(HttpServletResponse response) {

        String filename = "/realbootfile.efi";
        try {
            ServletOutputStream output = response.getOutputStream();

            InputStream input = servletContext.getResourceAsStream(filename);
            BufferedInputStream bufferedInput = new BufferedInputStream(input);
            int datum = bufferedInput.read();
            while (datum != -1) {
                output.write(datum);
                datum = bufferedInput.read();
                response.flushBuffer(); // <======= HERE
            }
            //output.flush();
            output.close();

        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}

Answer 1

A response is "committed" when the header has been sent, and it means that changes to response headers cannot be honored. It doesn't stop you from writing the response body.